cpython/Lib/test/test_fstring.py

# -*- coding: utf-8 -*-
# There are tests here with unicode string literals and
# identifiers. There's a code in ast.c that was added because of a
# failure with a non-ascii-only expression.  So, I have tests for
# that.  There are workarounds that would let me run tests for that
# code without unicode identifiers and strings, but just using them
# directly seems like the easiest and therefore safest thing to do.
# Unicode identifiers in tests is allowed by PEP 3131.

import ast
import datetime
import dis
import os
import re
import types
import decimal
import unittest
import warnings
from test import support
from test.support.os_helper import temp_cwd
from test.support.script_helper import assert_python_failure, assert_python_ok

a_global = 'global variable'

# You could argue that I'm too strict in looking for specific error
#  values with assertRaisesRegex, but without it it's way too easy to
#  make a syntax error in the test strings. Especially with all of the
#  triple quotes, raw strings, backslashes, etc. I think it's a
#  worthwhile tradeoff. When I switched to this method, I found many
#  examples where I wasn't testing what I thought I was.

class TestCase(unittest.TestCase):
    def assertAllRaise(self, exception_type, regex, error_strings):
        for str in error_strings:
            with self.subTest(str=str):
                with self.assertRaisesRegex(exception_type, regex):
                    eval(str)

    def test__format__lookup(self):
        # Make sure __format__ is looked up on the type, not the instance.
        class X:
            def __format__(self, spec):
                return 'class'

        x = X()

        # Add a bound __format__ method to the 'y' instance, but not
        #  the 'x' instance.
        y = X()
        y.__format__ = types.MethodType(lambda self, spec: 'instance', y)

        self.assertEqual(f'{y}', format(y))
        self.assertEqual(f'{y}', 'class')
        self.assertEqual(format(x), format(y))

        # __format__ is not called this way, but still make sure it
        #  returns what we expect (so we can make sure we're bypassing
        #  it).
        self.assertEqual(x.__format__(''), 'class')
        self.assertEqual(y.__format__(''), 'instance')

        # This is how __format__ is actually called.
        self.assertEqual(type(x).__format__(x, ''), 'class')
        self.assertEqual(type(y).__format__(y, ''), 'class')

    def test_ast(self):
        # Inspired by http://bugs.python.org/issue24975
        class X:
            def __init__(self):
                self.called = False
            def __call__(self):
                self.called = True
                return 4
        x = X()
        expr = """
a = 10
f'{a * x()}'"""
        t = ast.parse(expr)
        c = compile(t, '', 'exec')

        # Make sure x was not called.
        self.assertFalse(x.called)

        # Actually run the code.
        exec(c)

        # Make sure x was called.
        self.assertTrue(x.called)

    def test_ast_line_numbers(self):
        expr = """
a = 10
f'{a * x()}'"""
        t = ast.parse(expr)
        self.assertEqual(type(t), ast.Module)
        self.assertEqual(len(t.body), 2)
        # check `a = 10`
        self.assertEqual(type(t.body[0]), ast.Assign)
        self.assertEqual(t.body[0].lineno, 2)
        # check `f'...'`
        self.assertEqual(type(t.body[1]), ast.Expr)
        self.assertEqual(type(t.body[1].value), ast.JoinedStr)
        self.assertEqual(len(t.body[1].value.values), 1)
        self.assertEqual(type(t.body[1].value.values[0]), ast.FormattedValue)
        self.assertEqual(t.body[1].lineno, 3)
        self.assertEqual(t.body[1].value.lineno, 3)
        self.assertEqual(t.body[1].value.values[0].lineno, 3)
        # check the binop location
        binop = t.body[1].value.values[0].value
        self.assertEqual(type(binop), ast.BinOp)
        self.assertEqual(type(binop.left), ast.Name)
        self.assertEqual(type(binop.op), ast.Mult)
        self.assertEqual(type(binop.right), ast.Call)
        self.assertEqual(binop.lineno, 3)
        self.assertEqual(binop.left.lineno, 3)
        self.assertEqual(binop.right.lineno, 3)
        self.assertEqual(binop.col_offset, 3)
        self.assertEqual(binop.left.col_offset, 3)
        self.assertEqual(binop.right.col_offset, 7)

    def test_ast_line_numbers_multiple_formattedvalues(self):
        expr = """
f'no formatted values'
f'eggs {a * x()} spam {b + y()}'"""
        t = ast.parse(expr)
        self.assertEqual(type(t), ast.Module)
        self.assertEqual(len(t.body), 2)
        # check `f'no formatted value'`
        self.assertEqual(type(t.body[0]), ast.Expr)
        self.assertEqual(type(t.body[0].value), ast.JoinedStr)
        self.assertEqual(t.body[0].lineno, 2)
        # check `f'...'`
        self.assertEqual(type(t.body[1]), ast.Expr)
        self.assertEqual(type(t.body[1].value), ast.JoinedStr)
        self.assertEqual(len(t.body[1].value.values), 4)
        self.assertEqual(type(t.body[1].value.values[0]), ast.Constant)
        self.assertEqual(type(t.body[1].value.values[0].value), str)
        self.assertEqual(type(t.body[1].value.values[1]), ast.FormattedValue)
        self.assertEqual(type(t.body[1].value.values[2]), ast.Constant)
        self.assertEqual(type(t.body[1].value.values[2].value), str)
        self.assertEqual(type(t.body[1].value.values[3]), ast.FormattedValue)
        self.assertEqual(t.body[1].lineno, 3)
        self.assertEqual(t.body[1].value.lineno, 3)
        self.assertEqual(t.body[1].value.values[0].lineno, 3)
        self.assertEqual(t.body[1].value.values[1].lineno, 3)
        self.assertEqual(t.body[1].value.values[2].lineno, 3)
        self.assertEqual(t.body[1].value.values[3].lineno, 3)
        # check the first binop location
        binop1 = t.body[1].value.values[1].value
        self.assertEqual(type(binop1), ast.BinOp)
        self.assertEqual(type(binop1.left), ast.Name)
        self.assertEqual(type(binop1.op), ast.Mult)
        self.assertEqual(type(binop1.right), ast.Call)
        self.assertEqual(binop1.lineno, 3)
        self.assertEqual(binop1.left.lineno, 3)
        self.assertEqual(binop1.right.lineno, 3)
        self.assertEqual(binop1.col_offset, 8)
        self.assertEqual(binop1.left.col_offset, 8)
        self.assertEqual(binop1.right.col_offset, 12)
        # check the second binop location
        binop2 = t.body[1].value.values[3].value
        self.assertEqual(type(binop2), ast.BinOp)
        self.assertEqual(type(binop2.left), ast.Name)
        self.assertEqual(type(binop2.op), ast.Add)
        self.assertEqual(type(binop2.right), ast.Call)
        self.assertEqual(binop2.lineno, 3)
        self.assertEqual(binop2.left.lineno, 3)
        self.assertEqual(binop2.right.lineno, 3)
        self.assertEqual(binop2.col_offset, 23)
        self.assertEqual(binop2.left.col_offset, 23)
        self.assertEqual(binop2.right.col_offset, 27)

    def test_ast_line_numbers_nested(self):
        expr = """
a = 10
f'{a * f"-{x()}-"}'"""
        t = ast.parse(expr)
        self.assertEqual(type(t), ast.Module)
        self.assertEqual(len(t.body), 2)
        # check `a = 10`
        self.assertEqual(type(t.body[0]), ast.Assign)
        self.assertEqual(t.body[0].lineno, 2)
        # check `f'...'`
        self.assertEqual(type(t.body[1]), ast.Expr)
        self.assertEqual(type(t.body[1].value), ast.JoinedStr)
        self.assertEqual(len(t.body[1].value.values), 1)
        self.assertEqual(type(t.body[1].value.values[0]), ast.FormattedValue)
        self.assertEqual(t.body[1].lineno, 3)
        self.assertEqual(t.body[1].value.lineno, 3)
        self.assertEqual(t.body[1].value.values[0].lineno, 3)
        # check the binop location
        binop = t.body[1].value.values[0].value
        self.assertEqual(type(binop), ast.BinOp)
        self.assertEqual(type(binop.left), ast.Name)
        self.assertEqual(type(binop.op), ast.Mult)
        self.assertEqual(type(binop.right), ast.JoinedStr)
        self.assertEqual(binop.lineno, 3)
        self.assertEqual(binop.left.lineno, 3)
        self.assertEqual(binop.right.lineno, 3)
        self.assertEqual(binop.col_offset, 3)
        self.assertEqual(binop.left.col_offset, 3)
        self.assertEqual(binop.right.col_offset, 7)
        # check the nested call location
        self.assertEqual(len(binop.right.values), 3)
        self.assertEqual(type(binop.right.values[0]), ast.Constant)
        self.assertEqual(type(binop.right.values[0].value), str)
        self.assertEqual(type(binop.right.values[1]), ast.FormattedValue)
        self.assertEqual(type(binop.right.values[2]), ast.Constant)
        self.assertEqual(type(binop.right.values[2].value), str)
        self.assertEqual(binop.right.values[0].lineno, 3)
        self.assertEqual(binop.right.values[1].lineno, 3)
        self.assertEqual(binop.right.values[2].lineno, 3)
        call = binop.right.values[1].value
        self.assertEqual(type(call), ast.Call)
        self.assertEqual(call.lineno, 3)
        self.assertEqual(call.col_offset, 11)

    def test_ast_line_numbers_duplicate_expression(self):
        expr = """
a = 10
f'{a * x()} {a * x()} {a * x()}'
"""
        t = ast.parse(expr)
        self.assertEqual(type(t), ast.Module)
        self.assertEqual(len(t.body), 2)
        # check `a = 10`
        self.assertEqual(type(t.body[0]), ast.Assign)
        self.assertEqual(t.body[0].lineno, 2)
        # check `f'...'`
        self.assertEqual(type(t.body[1]), ast.Expr)
        self.assertEqual(type(t.body[1].value), ast.JoinedStr)
        self.assertEqual(len(t.body[1].value.values), 5)
        self.assertEqual(type(t.body[1].value.values[0]), ast.FormattedValue)
        self.assertEqual(type(t.body[1].value.values[1]), ast.Constant)
        self.assertEqual(type(t.body[1].value.values[1].value), str)
        self.assertEqual(type(t.body[1].value.values[2]), ast.FormattedValue)
        self.assertEqual(type(t.body[1].value.values[3]), ast.Constant)
        self.assertEqual(type(t.body[1].value.values[3].value), str)
        self.assertEqual(type(t.body[1].value.values[4]), ast.FormattedValue)
        self.assertEqual(t.body[1].lineno, 3)
        self.assertEqual(t.body[1].value.lineno, 3)
        self.assertEqual(t.body[1].value.values[0].lineno, 3)
        self.assertEqual(t.body[1].value.values[1].lineno, 3)
        self.assertEqual(t.body[1].value.values[2].lineno, 3)
        self.assertEqual(t.body[1].value.values[3].lineno, 3)
        self.assertEqual(t.body[1].value.values[4].lineno, 3)
        # check the first binop location
        binop = t.body[1].value.values[0].value
        self.assertEqual(type(binop), ast.BinOp)
        self.assertEqual(type(binop.left), ast.Name)
        self.assertEqual(type(binop.op), ast.Mult)
        self.assertEqual(type(binop.right), ast.Call)
        self.assertEqual(binop.lineno, 3)
        self.assertEqual(binop.left.lineno, 3)
        self.assertEqual(binop.right.lineno, 3)
        self.assertEqual(binop.col_offset, 3)
        self.assertEqual(binop.left.col_offset, 3)
        self.assertEqual(binop.right.col_offset, 7)
        # check the second binop location
        binop = t.body[1].value.values[2].value
        self.assertEqual(type(binop), ast.BinOp)
        self.assertEqual(type(binop.left), ast.Name)
        self.assertEqual(type(binop.op), ast.Mult)
        self.assertEqual(type(binop.right), ast.Call)
        self.assertEqual(binop.lineno, 3)
        self.assertEqual(binop.left.lineno, 3)
        self.assertEqual(binop.right.lineno, 3)
        self.assertEqual(binop.col_offset, 13)
        self.assertEqual(binop.left.col_offset, 13)
        self.assertEqual(binop.right.col_offset, 17)
        # check the third binop location
        binop = t.body[1].value.values[4].value
        self.assertEqual(type(binop), ast.BinOp)
        self.assertEqual(type(binop.left), ast.Name)
        self.assertEqual(type(binop.op), ast.Mult)
        self.assertEqual(type(binop.right), ast.Call)
        self.assertEqual(binop.lineno, 3)
        self.assertEqual(binop.left.lineno, 3)
        self.assertEqual(binop.right.lineno, 3)
        self.assertEqual(binop.col_offset, 23)
        self.assertEqual(binop.left.col_offset, 23)
        self.assertEqual(binop.right.col_offset, 27)

    def test_ast_numbers_fstring_with_formatting(self):

        t = ast.parse('f"Here is that pesky {xxx:.3f} again"')
        self.assertEqual(len(t.body), 1)
        self.assertEqual(t.body[0].lineno, 1)

        self.assertEqual(type(t.body[0]), ast.Expr)
        self.assertEqual(type(t.body[0].value), ast.JoinedStr)
        self.assertEqual(len(t.body[0].value.values), 3)

        self.assertEqual(type(t.body[0].value.values[0]), ast.Constant)
        self.assertEqual(type(t.body[0].value.values[1]), ast.FormattedValue)
        self.assertEqual(type(t.body[0].value.values[2]), ast.Constant)

        _, expr, _ = t.body[0].value.values

        name = expr.value
        self.assertEqual(type(name), ast.Name)
        self.assertEqual(name.lineno, 1)
        self.assertEqual(name.end_lineno, 1)
        self.assertEqual(name.col_offset, 22)
        self.assertEqual(name.end_col_offset, 25)

    def test_ast_line_numbers_multiline_fstring(self):
        # See bpo-30465 for details.
        expr = """
a = 10
f'''
  {a
     *
       x()}
non-important content
'''
"""
        t = ast.parse(expr)
        self.assertEqual(type(t), ast.Module)
        self.assertEqual(len(t.body), 2)
        # check `a = 10`
        self.assertEqual(type(t.body[0]), ast.Assign)
        self.assertEqual(t.body[0].lineno, 2)
        # check `f'...'`
        self.assertEqual(type(t.body[1]), ast.Expr)
        self.assertEqual(type(t.body[1].value), ast.JoinedStr)
        self.assertEqual(len(t.body[1].value.values), 3)
        self.assertEqual(type(t.body[1].value.values[0]), ast.Constant)
        self.assertEqual(type(t.body[1].value.values[0].value), str)
        self.assertEqual(type(t.body[1].value.values[1]), ast.FormattedValue)
        self.assertEqual(type(t.body[1].value.values[2]), ast.Constant)
        self.assertEqual(type(t.body[1].value.values[2].value), str)
        self.assertEqual(t.body[1].lineno, 3)
        self.assertEqual(t.body[1].value.lineno, 3)
        self.assertEqual(t.body[1].value.values[0].lineno, 3)
        self.assertEqual(t.body[1].value.values[1].lineno, 4)
        self.assertEqual(t.body[1].value.values[2].lineno, 6)
        self.assertEqual(t.body[1].col_offset, 0)
        self.assertEqual(t.body[1].value.col_offset, 0)
        self.assertEqual(t.body[1].value.values[0].col_offset, 4)
        self.assertEqual(t.body[1].value.values[1].col_offset, 2)
        self.assertEqual(t.body[1].value.values[2].col_offset, 11)
        # NOTE: the following lineno information and col_offset is correct for
        # expressions within FormattedValues.
        binop = t.body[1].value.values[1].value
        self.assertEqual(type(binop), ast.BinOp)
        self.assertEqual(type(binop.left), ast.Name)
        self.assertEqual(type(binop.op), ast.Mult)
        self.assertEqual(type(binop.right), ast.Call)
        self.assertEqual(binop.lineno, 4)
        self.assertEqual(binop.left.lineno, 4)
        self.assertEqual(binop.right.lineno, 6)
        self.assertEqual(binop.col_offset, 3)
        self.assertEqual(binop.left.col_offset, 3)
        self.assertEqual(binop.right.col_offset, 7)

        expr = """
a = f'''
          {blech}
    '''
"""
        t = ast.parse(expr)
        self.assertEqual(type(t), ast.Module)
        self.assertEqual(len(t.body), 1)
        # Check f'...'
        self.assertEqual(type(t.body[0]), ast.Assign)
        self.assertEqual(type(t.body[0].value), ast.JoinedStr)
        self.assertEqual(len(t.body[0].value.values), 3)
        self.assertEqual(type(t.body[0].value.values[1]), ast.FormattedValue)
        self.assertEqual(t.body[0].lineno, 2)
        self.assertEqual(t.body[0].value.lineno, 2)
        self.assertEqual(t.body[0].value.values[0].lineno, 2)
        self.assertEqual(t.body[0].value.values[1].lineno, 3)
        self.assertEqual(t.body[0].value.values[2].lineno, 3)
        self.assertEqual(t.body[0].col_offset, 0)
        self.assertEqual(t.body[0].value.col_offset, 4)
        self.assertEqual(t.body[0].value.values[0].col_offset, 8)
        self.assertEqual(t.body[0].value.values[1].col_offset, 10)
        self.assertEqual(t.body[0].value.values[2].col_offset, 17)
        # Check {blech}
        self.assertEqual(t.body[0].value.values[1].value.lineno, 3)
        self.assertEqual(t.body[0].value.values[1].value.end_lineno, 3)
        self.assertEqual(t.body[0].value.values[1].value.col_offset, 11)
        self.assertEqual(t.body[0].value.values[1].value.end_col_offset, 16)

    def test_ast_line_numbers_with_parentheses(self):
        expr = """
x = (
    f" {test(t)}"
)"""
        t = ast.parse(expr)
        self.assertEqual(type(t), ast.Module)
        self.assertEqual(len(t.body), 1)
        # check the joinedstr location
        joinedstr = t.body[0].value
        self.assertEqual(type(joinedstr), ast.JoinedStr)
        self.assertEqual(joinedstr.lineno, 3)
        self.assertEqual(joinedstr.end_lineno, 3)
        self.assertEqual(joinedstr.col_offset, 4)
        self.assertEqual(joinedstr.end_col_offset, 17)
        # check the formatted value location
        fv = t.body[0].value.values[1]
        self.assertEqual(type(fv), ast.FormattedValue)
        self.assertEqual(fv.lineno, 3)
        self.assertEqual(fv.end_lineno, 3)
        self.assertEqual(fv.col_offset, 7)
        self.assertEqual(fv.end_col_offset, 16)
        # check the test(t) location
        call = t.body[0].value.values[1].value
        self.assertEqual(type(call), ast.Call)
        self.assertEqual(call.lineno, 3)
        self.assertEqual(call.end_lineno, 3)
        self.assertEqual(call.col_offset, 8)
        self.assertEqual(call.end_col_offset, 15)

        expr = """
x = (
    u'wat',
    u"wat",
    b'wat',
    b"wat",
    f'wat',
    f"wat",
)

y = (
    u'''wat''',
    u\"\"\"wat\"\"\",
    b'''wat''',
    b\"\"\"wat\"\"\",
    f'''wat''',
    f\"\"\"wat\"\"\",
)
        """
        t = ast.parse(expr)
        self.assertEqual(type(t), ast.Module)
        self.assertEqual(len(t.body), 2)
        x, y = t.body

        # Check the single quoted string offsets first.
        offsets = [
            (elt.col_offset, elt.end_col_offset)
            for elt in x.value.elts
        ]
        self.assertTrue(all(
            offset == (4, 10)
            for offset in offsets
        ))

        # Check the triple quoted string offsets.
        offsets = [
            (elt.col_offset, elt.end_col_offset)
            for elt in y.value.elts
        ]
        self.assertTrue(all(
            offset == (4, 14)
            for offset in offsets
        ))

        expr = """
x = (
        'PERL_MM_OPT', (
            f'wat'
            f'some_string={f(x)} '
            f'wat'
        ),
)
"""
        t = ast.parse(expr)
        self.assertEqual(type(t), ast.Module)
        self.assertEqual(len(t.body), 1)
        # check the fstring
        fstring = t.body[0].value.elts[1]
        self.assertEqual(type(fstring), ast.JoinedStr)
        self.assertEqual(len(fstring.values), 3)
        wat1, middle, wat2 = fstring.values
        # check the first wat
        self.assertEqual(type(wat1), ast.Constant)
        self.assertEqual(wat1.lineno, 4)
        self.assertEqual(wat1.end_lineno, 5)
        self.assertEqual(wat1.col_offset, 14)
        self.assertEqual(wat1.end_col_offset, 26)
        # check the call
        call = middle.value
        self.assertEqual(type(call), ast.Call)
        self.assertEqual(call.lineno, 5)
        self.assertEqual(call.end_lineno, 5)
        self.assertEqual(call.col_offset, 27)
        self.assertEqual(call.end_col_offset, 31)
        # check the second wat
        self.assertEqual(type(wat2), ast.Constant)
        self.assertEqual(wat2.lineno, 5)
        self.assertEqual(wat2.end_lineno, 6)
        self.assertEqual(wat2.col_offset, 32)
        # wat ends at the offset 17, but the whole f-string
        # ends at the offset 18 (since the quote is part of the
        # f-string but not the wat string)
        self.assertEqual(wat2.end_col_offset, 17)
        self.assertEqual(fstring.end_col_offset, 18)

    def test_ast_fstring_empty_format_spec(self):
        expr = "f'{expr:}'"

        mod = ast.parse(expr)
        self.assertEqual(type(mod), ast.Module)
        self.assertEqual(len(mod.body), 1)

        fstring = mod.body[0].value
        self.assertEqual(type(fstring), ast.JoinedStr)
        self.assertEqual(len(fstring.values), 1)

        fv = fstring.values[0]
        self.assertEqual(type(fv), ast.FormattedValue)

        format_spec = fv.format_spec
        self.assertEqual(type(format_spec), ast.JoinedStr)
        self.assertEqual(len(format_spec.values), 0)

    def test_ast_fstring_format_spec(self):
        expr = "f'{1:{name}}'"

        mod = ast.parse(expr)
        self.assertEqual(type(mod), ast.Module)
        self.assertEqual(len(mod.body), 1)

        fstring = mod.body[0].value
        self.assertEqual(type(fstring), ast.JoinedStr)
        self.assertEqual(len(fstring.values), 1)

        fv = fstring.values[0]
        self.assertEqual(type(fv), ast.FormattedValue)

        format_spec = fv.format_spec
        self.assertEqual(type(format_spec), ast.JoinedStr)
        self.assertEqual(len(format_spec.values), 1)

        format_spec_value = format_spec.values[0]
        self.assertEqual(type(format_spec_value), ast.FormattedValue)
        self.assertEqual(format_spec_value.value.id, 'name')

        expr = "f'{1:{name1}{name2}}'"

        mod = ast.parse(expr)
        self.assertEqual(type(mod), ast.Module)
        self.assertEqual(len(mod.body), 1)

        fstring = mod.body[0].value
        self.assertEqual(type(fstring), ast.JoinedStr)
        self.assertEqual(len(fstring.values), 1)

        fv = fstring.values[0]
        self.assertEqual(type(fv), ast.FormattedValue)

        format_spec = fv.format_spec
        self.assertEqual(type(format_spec), ast.JoinedStr)
        self.assertEqual(len(format_spec.values), 2)

        format_spec_value = format_spec.values[0]
        self.assertEqual(type(format_spec_value), ast.FormattedValue)
        self.assertEqual(format_spec_value.value.id, 'name1')

        format_spec_value = format_spec.values[1]
        self.assertEqual(type(format_spec_value), ast.FormattedValue)
        self.assertEqual(format_spec_value.value.id, 'name2')


    def test_docstring(self):
        def f():
            f'''Not a docstring'''
        self.assertIsNone(f.__doc__)
        def g():
            '''Not a docstring''' \
            f''
        self.assertIsNone(g.__doc__)

    def test_literal_eval(self):
        with self.assertRaisesRegex(ValueError, 'malformed node or string'):
            ast.literal_eval("f'x'")

    def test_ast_compile_time_concat(self):
        x = ['']

        expr = """x[0] = 'foo' f'{3}'"""
        t = ast.parse(expr)
        c = compile(t, '', 'exec')
        exec(c)
        self.assertEqual(x[0], 'foo3')

    def test_compile_time_concat_errors(self):
        self.assertAllRaise(SyntaxError,
                            'cannot mix bytes and nonbytes literals',
                            [r"""f'' b''""",
                             r"""b'' f''""",
                             ])

    def test_literal(self):
        self.assertEqual(f'', '')
        self.assertEqual(f'a', 'a')
        self.assertEqual(f' ', ' ')

    def test_unterminated_string(self):
        self.assertAllRaise(SyntaxError, 'unterminated string',
                            [r"""f'{"x'""",
                             r"""f'{"x}'""",
                             r"""f'{("x'""",
                             r"""f'{("x}'""",
                             ])

    @unittest.skipIf(support.is_wasi, "exhausts limited stack on WASI")
    def test_mismatched_parens(self):
        self.assertAllRaise(SyntaxError, r"closing parenthesis '\}' "
                            r"does not match opening parenthesis '\('",
                            ["f'{((}'",
                             ])
        self.assertAllRaise(SyntaxError, r"closing parenthesis '\)' "
                            r"does not match opening parenthesis '\['",
                            ["f'{a[4)}'",
                            ])
        self.assertAllRaise(SyntaxError, r"closing parenthesis '\]' "
                            r"does not match opening parenthesis '\('",
                            ["f'{a(4]}'",
                            ])
        self.assertAllRaise(SyntaxError, r"closing parenthesis '\}' "
                            r"does not match opening parenthesis '\['",
                            ["f'{a[4}'",
                            ])
        self.assertAllRaise(SyntaxError, r"closing parenthesis '\}' "
                            r"does not match opening parenthesis '\('",
                            ["f'{a(4}'",
                            ])
        self.assertRaises(SyntaxError, eval, "f'{" + "("*500 + "}'")

    @unittest.skipIf(support.is_wasi, "exhausts limited stack on WASI")
    def test_fstring_nested_too_deeply(self):
        self.assertAllRaise(SyntaxError,
                            "f-string: expressions nested too deeply",
                            ['f"{1+2:{1+2:{1+1:{1}}}}"'])

        def create_nested_fstring(n):
            if n == 0:
                return "1+1"
            prev = create_nested_fstring(n-1)
            return f'f"{{{prev}}}"'

        self.assertAllRaise(SyntaxError,
                            "too many nested f-strings",
                            [create_nested_fstring(160)])

    def test_syntax_error_in_nested_fstring(self):
        # See gh-104016 for more information on this crash
        self.assertAllRaise(SyntaxError,
                            "invalid syntax",
                            ['f"{1 1:' + ('{f"1:' * 199)])

    def test_double_braces(self):
        self.assertEqual(f'{{', '{')
        self.assertEqual(f'a{{', 'a{')
        self.assertEqual(f'{{b', '{b')
        self.assertEqual(f'a{{b', 'a{b')
        self.assertEqual(f'}}', '}')
        self.assertEqual(f'a}}', 'a}')
        self.assertEqual(f'}}b', '}b')
        self.assertEqual(f'a}}b', 'a}b')
        self.assertEqual(f'{{}}', '{}')
        self.assertEqual(f'a{{}}', 'a{}')
        self.assertEqual(f'{{b}}', '{b}')
        self.assertEqual(f'{{}}c', '{}c')
        self.assertEqual(f'a{{b}}', 'a{b}')
        self.assertEqual(f'a{{}}c', 'a{}c')
        self.assertEqual(f'{{b}}c', '{b}c')
        self.assertEqual(f'a{{b}}c', 'a{b}c')

        self.assertEqual(f'{{{10}', '{10')
        self.assertEqual(f'}}{10}', '}10')
        self.assertEqual(f'}}{{{10}', '}{10')
        self.assertEqual(f'}}a{{{10}', '}a{10')

        self.assertEqual(f'{10}{{', '10{')
        self.assertEqual(f'{10}}}', '10}')
        self.assertEqual(f'{10}}}{{', '10}{')
        self.assertEqual(f'{10}}}a{{' '}', '10}a{}')

        # Inside of strings, don't interpret doubled brackets.
        self.assertEqual(f'{"{{}}"}', '{{}}')

        self.assertAllRaise(TypeError, 'unhashable type',
                            ["f'{ {{}} }'", # dict in a set
                             ])

    def test_compile_time_concat(self):
        x = 'def'
        self.assertEqual('abc' f'## {x}ghi', 'abc## defghi')
        self.assertEqual('abc' f'{x}' 'ghi', 'abcdefghi')
        self.assertEqual('abc' f'{x}' 'gh' f'i{x:4}', 'abcdefghidef ')
        self.assertEqual('{x}' f'{x}', '{x}def')
        self.assertEqual('{x' f'{x}', '{xdef')
        self.assertEqual('{x}' f'{x}', '{x}def')
        self.assertEqual('{{x}}' f'{x}', '{{x}}def')
        self.assertEqual('{{x' f'{x}', '{{xdef')
        self.assertEqual('x}}' f'{x}', 'x}}def')
        self.assertEqual(f'{x}' 'x}}', 'defx}}')
        self.assertEqual(f'{x}' '', 'def')
        self.assertEqual('' f'{x}' '', 'def')
        self.assertEqual('' f'{x}', 'def')
        self.assertEqual(f'{x}' '2', 'def2')
        self.assertEqual('1' f'{x}' '2', '1def2')
        self.assertEqual('1' f'{x}', '1def')
        self.assertEqual(f'{x}' f'-{x}', 'def-def')
        self.assertEqual('' f'', '')
        self.assertEqual('' f'' '', '')
        self.assertEqual('' f'' '' f'', '')
        self.assertEqual(f'', '')
        self.assertEqual(f'' '', '')
        self.assertEqual(f'' '' f'', '')
        self.assertEqual(f'' '' f'' '', '')

        # This is not really [f'{'] + [f'}'] since we treat the inside
        # of braces as a purely new context, so it is actually f'{ and
        # then eval('  f') (a valid expression) and then }' which would
        # constitute a valid f-string.
        self.assertEqual(f'{' f'}', ' f')

        self.assertAllRaise(SyntaxError, "expecting '}'",
                            ['''f'{3' f"}"''',  # can't concat to get a valid f-string
                             ])

    def test_comments(self):
        # These aren't comments, since they're in strings.
        d = {'#': 'hash'}
        self.assertEqual(f'{"#"}', '#')
        self.assertEqual(f'{d["#"]}', 'hash')

        self.assertAllRaise(SyntaxError, "'{' was never closed",
                            ["f'{1#}'",   # error because everything after '#' is a comment
                             "f'{#}'",
                             "f'one: {1#}'",
                             "f'{1# one} {2 this is a comment still#}'",
                             ])
        self.assertAllRaise(SyntaxError, r"f-string: unmatched '\)'",
                            ["f'{)#}'",   # When wrapped in parens, this becomes
                                          #  '()#)'.  Make sure that doesn't compile.
                             ])
        self.assertEqual(f'''A complex trick: {
2  # two
}''', 'A complex trick: 2')
        self.assertEqual(f'''
{
40 # fourty
+  # plus
2  # two
}''', '\n42')
        self.assertEqual(f'''
{
40 # fourty
+  # plus
2  # two
}''', '\n42')

        self.assertEqual(f'''
# this is not a comment
{ # the following operation it's
3 # this is a number
* 2}''', '\n# this is not a comment\n6')
        self.assertEqual(f'''
{# f'a {comment}'
86 # constant
# nothing more
}''', '\n86')

        self.assertAllRaise(SyntaxError, r"f-string: valid expression required before '}'",
                            ["""f'''
{
# only a comment
}'''
""", # this is equivalent to f'{}'
                             ])

    def test_many_expressions(self):
        # Create a string with many expressions in it. Note that
        #  because we have a space in here as a literal, we're actually
        #  going to use twice as many ast nodes: one for each literal
        #  plus one for each expression.
        def build_fstr(n, extra=''):
            return "f'" + ('{x} ' * n) + extra + "'"

        x = 'X'
        width = 1

        # Test around 256.
        for i in range(250, 260):
            self.assertEqual(eval(build_fstr(i)), (x+' ')*i)

        # Test concatenating 2 largs fstrings.
        self.assertEqual(eval(build_fstr(255)*256), (x+' ')*(255*256))

        s = build_fstr(253, '{x:{width}} ')
        self.assertEqual(eval(s), (x+' ')*254)

        # Test lots of expressions and constants, concatenated.
        s = "f'{1}' 'x' 'y'" * 1024
        self.assertEqual(eval(s), '1xy' * 1024)

    def test_format_specifier_expressions(self):
        width = 10
        precision = 4
        value = decimal.Decimal('12.34567')
        self.assertEqual(f'result: {value:{width}.{precision}}', 'result:      12.35')
        self.assertEqual(f'result: {value:{width!r}.{precision}}', 'result:      12.35')
        self.assertEqual(f'result: {value:{width:0}.{precision:1}}', 'result:      12.35')
        self.assertEqual(f'result: {value:{1}{0:0}.{precision:1}}', 'result:      12.35')
        self.assertEqual(f'result: {value:{ 1}{ 0:0}.{ precision:1}}', 'result:      12.35')
        self.assertEqual(f'{10:#{1}0x}', '       0xa')
        self.assertEqual(f'{10:{"#"}1{0}{"x"}}', '       0xa')
        self.assertEqual(f'{-10:-{"#"}1{0}x}', '      -0xa')
        self.assertEqual(f'{-10:{"-"}#{1}0{"x"}}', '      -0xa')
        self.assertEqual(f'{10:#{3 != {4:5} and width}x}', '       0xa')
        self.assertEqual(f'result: {value:{width:{0}}.{precision:1}}', 'result:      12.35')

        self.assertAllRaise(SyntaxError, "f-string: expecting ':' or '}'",
                            ["""f'{"s"!r{":10"}}'""",
                             # This looks like a nested format spec.
                             ])

        self.assertAllRaise(SyntaxError,
                            "f-string: expecting a valid expression after '{'",
                            [# Invalid syntax inside a nested spec.
                             "f'{4:{/5}}'",
                             ])

        self.assertAllRaise(SyntaxError, 'f-string: invalid conversion character',
                            [# No expansion inside conversion or for
                             #  the : or ! itself.
                             """f'{"s"!{"r"}}'""",
                             ])

    def test_custom_format_specifier(self):
        class CustomFormat:
            def __format__(self, format_spec):
                return format_spec

        self.assertEqual(f'{CustomFormat():\n}', '\n')
        self.assertEqual(f'{CustomFormat():\u2603}', '☃')
        with self.assertWarns(SyntaxWarning):
            exec(r'f"{F():¯\_(ツ)_/¯}"', {'F': CustomFormat})

    def test_side_effect_order(self):
        class X:
            def __init__(self):
                self.i = 0
            def __format__(self, spec):
                self.i += 1
                return str(self.i)

        x = X()
        self.assertEqual(f'{x} {x}', '1 2')

    def test_missing_expression(self):
        self.assertAllRaise(SyntaxError,
                            "f-string: valid expression required before '}'",
                            ["f'{}'",
                             "f'{ }'"
                             "f' {} '",
                             "f'{10:{ }}'",
                             "f' { } '",

                             # The Python parser ignores also the following
                             # whitespace characters in additional to a space.
                             "f'''{\t\f\r\n}'''",
                             ])

        self.assertAllRaise(SyntaxError,
                            "f-string: valid expression required before '!'",
                            ["f'{!r}'",
                             "f'{ !r}'",
                             "f'{!}'",
                             "f'''{\t\f\r\n!a}'''",

                             # Catch empty expression before the
                             #  missing closing brace.
                             "f'{!'",
                             "f'{!s:'",

                             # Catch empty expression before the
                             #  invalid conversion.
                             "f'{!x}'",
                             "f'{ !xr}'",
                             "f'{!x:}'",
                             "f'{!x:a}'",
                             "f'{ !xr:}'",
                             "f'{ !xr:a}'",
                             ])

        self.assertAllRaise(SyntaxError,
                            "f-string: valid expression required before ':'",
                            ["f'{:}'",
                             "f'{ :!}'",
                             "f'{:2}'",
                             "f'''{\t\f\r\n:a}'''",
                             "f'{:'",
                             "F'{[F'{:'}[F'{:'}]]]",
                             ])

        self.assertAllRaise(SyntaxError,
                            "f-string: valid expression required before '='",
                            ["f'{=}'",
                             "f'{ =}'",
                             "f'{ =:}'",
                             "f'{   =!}'",
                             "f'''{\t\f\r\n=}'''",
                             "f'{='",
                             ])

        # Different error message is raised for other whitespace characters.
        self.assertAllRaise(SyntaxError, r"invalid non-printable character U\+00A0",
                            ["f'''{\xa0}'''",
                             "\xa0",
                             ])

    def test_parens_in_expressions(self):
        self.assertEqual(f'{3,}', '(3,)')

        self.assertAllRaise(SyntaxError,
                            "f-string: expecting a valid expression after '{'",
                            ["f'{,}'",
                             ])

        self.assertAllRaise(SyntaxError, r"f-string: unmatched '\)'",
                            ["f'{3)+(4}'",
                             ])

    def test_newlines_before_syntax_error(self):
        self.assertAllRaise(SyntaxError,
                            "f-string: expecting a valid expression after '{'",
                ["f'{.}'", "\nf'{.}'", "\n\nf'{.}'"])

    def test_backslashes_in_string_part(self):
        self.assertEqual(f'\t', '\t')
        self.assertEqual(r'\t', '\\t')
        self.assertEqual(rf'\t', '\\t')
        self.assertEqual(f'{2}\t', '2\t')
        self.assertEqual(f'{2}\t{3}', '2\t3')
        self.assertEqual(f'\t{3}', '\t3')

        self.assertEqual(f'\u0394', '\u0394')
        self.assertEqual(r'\u0394', '\\u0394')
        self.assertEqual(rf'\u0394', '\\u0394')
        self.assertEqual(f'{2}\u0394', '2\u0394')
        self.assertEqual(f'{2}\u0394{3}', '2\u03943')
        self.assertEqual(f'\u0394{3}', '\u03943')

        self.assertEqual(f'\U00000394', '\u0394')
        self.assertEqual(r'\U00000394', '\\U00000394')
        self.assertEqual(rf'\U00000394', '\\U00000394')
        self.assertEqual(f'{2}\U00000394', '2\u0394')
        self.assertEqual(f'{2}\U00000394{3}', '2\u03943')
        self.assertEqual(f'\U00000394{3}', '\u03943')

        self.assertEqual(f'\N{GREEK CAPITAL LETTER DELTA}', '\u0394')
        self.assertEqual(f'{2}\N{GREEK CAPITAL LETTER DELTA}', '2\u0394')
        self.assertEqual(f'{2}\N{GREEK CAPITAL LETTER DELTA}{3}', '2\u03943')
        self.assertEqual(f'\N{GREEK CAPITAL LETTER DELTA}{3}', '\u03943')
        self.assertEqual(f'2\N{GREEK CAPITAL LETTER DELTA}', '2\u0394')
        self.assertEqual(f'2\N{GREEK CAPITAL LETTER DELTA}3', '2\u03943')
        self.assertEqual(f'\N{GREEK CAPITAL LETTER DELTA}3', '\u03943')

        self.assertEqual(f'\x20', ' ')
        self.assertEqual(r'\x20', '\\x20')
        self.assertEqual(rf'\x20', '\\x20')
        self.assertEqual(f'{2}\x20', '2 ')
        self.assertEqual(f'{2}\x20{3}', '2 3')
        self.assertEqual(f'\x20{3}', ' 3')

        self.assertEqual(f'2\x20', '2 ')
        self.assertEqual(f'2\x203', '2 3')
        self.assertEqual(f'\x203', ' 3')

        with self.assertWarns(SyntaxWarning):  # invalid escape sequence
            value = eval(r"f'\{6*7}'")
        self.assertEqual(value, '\\42')
        with self.assertWarns(SyntaxWarning):  # invalid escape sequence
            value = eval(r"f'\g'")
        self.assertEqual(value, '\\g')
        self.assertEqual(f'\\{6*7}', '\\42')
        self.assertEqual(fr'\{6*7}', '\\42')

        AMPERSAND = 'spam'
        # Get the right unicode character (&), or pick up local variable
        # depending on the number of backslashes.
        self.assertEqual(f'\N{AMPERSAND}', '&')
        self.assertEqual(f'\\N{AMPERSAND}', '\\Nspam')
        self.assertEqual(fr'\N{AMPERSAND}', '\\Nspam')
        self.assertEqual(f'\\\N{AMPERSAND}', '\\&')

    def test_misformed_unicode_character_name(self):
        # These test are needed because unicode names are parsed
        # differently inside f-strings.
        self.assertAllRaise(SyntaxError, r"\(unicode error\) 'unicodeescape' codec can't decode bytes in position .*: malformed \\N character escape",
                            [r"f'\N'",
                             r"f'\N '",
                             r"f'\N  '",  # See bpo-46503.
                             r"f'\N{'",
                             r"f'\N{GREEK CAPITAL LETTER DELTA'",

                             # Here are the non-f-string versions,
                             #  which should give the same errors.
                             r"'\N'",
                             r"'\N '",
                             r"'\N  '",
                             r"'\N{'",
                             r"'\N{GREEK CAPITAL LETTER DELTA'",
                             ])

    def test_backslashes_in_expression_part(self):
        self.assertEqual(f"{(
                        1 +
                        2
        )}", "3")

        self.assertEqual("\N{LEFT CURLY BRACKET}", '{')
        self.assertEqual(f'{"\N{LEFT CURLY BRACKET}"}', '{')
        self.assertEqual(rf'{"\N{LEFT CURLY BRACKET}"}', '{')

        self.assertAllRaise(SyntaxError,
                            "f-string: valid expression required before '}'",
                            ["f'{\n}'",
                             ])

    def test_invalid_backslashes_inside_fstring_context(self):
        # All of these variations are invalid python syntax,
        # so they are also invalid in f-strings as well.
        cases = [
            formatting.format(expr=expr)
            for formatting in [
                "{expr}",
                "f'{{{expr}}}'",
                "rf'{{{expr}}}'",
            ]
            for expr in [
                r"\'a\'",
                r"\t3",
                r"\\"[0],
            ]
        ]
        self.assertAllRaise(SyntaxError, 'unexpected character after line continuation',
                            cases)

    def test_no_escapes_for_braces(self):
        """
        Only literal curly braces begin an expression.
        """
        # \x7b is '{'.
        self.assertEqual(f'\x7b1+1}}', '{1+1}')
        self.assertEqual(f'\x7b1+1', '{1+1')
        self.assertEqual(f'\u007b1+1', '{1+1')
        self.assertEqual(f'\N{LEFT CURLY BRACKET}1+1\N{RIGHT CURLY BRACKET}', '{1+1}')

    def test_newlines_in_expressions(self):
        self.assertEqual(f'{0}', '0')
        self.assertEqual(rf'''{3+
4}''', '7')

    def test_lambda(self):
        x = 5
        self.assertEqual(f'{(lambda y:x*y)("8")!r}', "'88888'")
        self.assertEqual(f'{(lambda y:x*y)("8")!r:10}', "'88888'   ")
        self.assertEqual(f'{(lambda y:x*y)("8"):10}', "88888     ")

        # lambda doesn't work without parens, because the colon
        # makes the parser think it's a format_spec
        # emit warning if we can match a format_spec
        self.assertAllRaise(SyntaxError,
                            "f-string: lambda expressions are not allowed "
                            "without parentheses",
                            ["f'{lambda x:x}'",
                             "f'{lambda :x}'",
                             "f'{lambda *arg, :x}'",
                             "f'{1, lambda:x}'",
                             "f'{lambda x:}'",
                             "f'{lambda :}'",
                             ])
        # Ensure the detection of invalid lambdas doesn't trigger detection
        # for valid lambdas in the second error pass
        with self.assertRaisesRegex(SyntaxError, "invalid syntax"):
            compile("lambda name_3=f'{name_4}': {name_3}\n1 $ 1", "<string>", "exec")

        # but don't emit the paren warning in general cases
        with self.assertRaisesRegex(SyntaxError, "f-string: expecting a valid expression after '{'"):
            eval("f'{+ lambda:None}'")

    def test_valid_prefixes(self):
        self.assertEqual(F'{1}', "1")
        self.assertEqual(FR'{2}', "2")
        self.assertEqual(fR'{3}', "3")

    def test_roundtrip_raw_quotes(self):
        self.assertEqual(fr"\'", "\\'")
        self.assertEqual(fr'\"', '\\"')
        self.assertEqual(fr'\"\'', '\\"\\\'')
        self.assertEqual(fr'\'\"', '\\\'\\"')
        self.assertEqual(fr'\"\'\"', '\\"\\\'\\"')
        self.assertEqual(fr'\'\"\'', '\\\'\\"\\\'')
        self.assertEqual(fr'\"\'\"\'', '\\"\\\'\\"\\\'')

    def test_fstring_backslash_before_double_bracket(self):
        deprecated_cases = [
            (r"f'\{{\}}'",   '\\{\\}'),
            (r"f'\{{'",      '\\{'),
            (r"f'\{{{1+1}'", '\\{2'),
            (r"f'\}}{1+1}'", '\\}2'),
            (r"f'{1+1}\}}'", '2\\}')
        ]
        for case, expected_result in deprecated_cases:
            with self.subTest(case=case, expected_result=expected_result):
                with self.assertWarns(SyntaxWarning):
                    result = eval(case)
                self.assertEqual(result, expected_result)
        self.assertEqual(fr'\{{\}}', '\\{\\}')
        self.assertEqual(fr'\{{', '\\{')
        self.assertEqual(fr'\{{{1+1}', '\\{2')
        self.assertEqual(fr'\}}{1+1}', '\\}2')
        self.assertEqual(fr'{1+1}\}}', '2\\}')

    def test_fstring_backslash_before_double_bracket_warns_once(self):
        with self.assertWarns(SyntaxWarning) as w:
            eval(r"f'\{{'")
        self.assertEqual(len(w.warnings), 1)
        self.assertEqual(w.warnings[0].category, SyntaxWarning)

    def test_fstring_backslash_prefix_raw(self):
        self.assertEqual(f'\\', '\\')
        self.assertEqual(f'\\\\', '\\\\')
        self.assertEqual(fr'\\', r'\\')
        self.assertEqual(fr'\\\\', r'\\\\')
        self.assertEqual(rf'\\', r'\\')
        self.assertEqual(rf'\\\\', r'\\\\')
        self.assertEqual(Rf'\\', R'\\')
        self.assertEqual(Rf'\\\\', R'\\\\')
        self.assertEqual(fR'\\', R'\\')
        self.assertEqual(fR'\\\\', R'\\\\')
        self.assertEqual(FR'\\', R'\\')
        self.assertEqual(FR'\\\\', R'\\\\')

    def test_fstring_format_spec_greedy_matching(self):
        self.assertEqual(f"{1:}}}", "1}")
        self.assertEqual(f"{1:>3{5}}}}", "                                  1}")

    def test_yield(self):
        # Not terribly useful, but make sure the yield turns
        #  a function into a generator
        def fn(y):
            f'y:{yield y*2}'
            f'{yield}'

        g = fn(4)
        self.assertEqual(next(g), 8)
        self.assertEqual(next(g), None)

    def test_yield_send(self):
        def fn(x):
            yield f'x:{yield (lambda i: x * i)}'

        g = fn(10)
        the_lambda = next(g)
        self.assertEqual(the_lambda(4), 40)
        self.assertEqual(g.send('string'), 'x:string')

    def test_expressions_with_triple_quoted_strings(self):
        self.assertEqual(f"{'''x'''}", 'x')
        self.assertEqual(f"{'''eric's'''}", "eric's")

        # Test concatenation within an expression
        self.assertEqual(f'{"x" """eric"s""" "y"}', 'xeric"sy')
        self.assertEqual(f'{"x" """eric"s"""}', 'xeric"s')
        self.assertEqual(f'{"""eric"s""" "y"}', 'eric"sy')
        self.assertEqual(f'{"""x""" """eric"s""" "y"}', 'xeric"sy')
        self.assertEqual(f'{"""x""" """eric"s""" """y"""}', 'xeric"sy')
        self.assertEqual(f'{r"""x""" """eric"s""" """y"""}', 'xeric"sy')

    def test_multiple_vars(self):
        x = 98
        y = 'abc'
        self.assertEqual(f'{x}{y}', '98abc')

        self.assertEqual(f'X{x}{y}', 'X98abc')
        self.assertEqual(f'{x}X{y}', '98Xabc')
        self.assertEqual(f'{x}{y}X', '98abcX')

        self.assertEqual(f'X{x}Y{y}', 'X98Yabc')
        self.assertEqual(f'X{x}{y}Y', 'X98abcY')
        self.assertEqual(f'{x}X{y}Y', '98XabcY')

        self.assertEqual(f'X{x}Y{y}Z', 'X98YabcZ')

    def test_closure(self):
        def outer(x):
            def inner():
                return f'x:{x}'
            return inner

        self.assertEqual(outer('987')(), 'x:987')
        self.assertEqual(outer(7)(), 'x:7')

    def test_arguments(self):
        y = 2
        def f(x, width):
            return f'x={x*y:{width}}'

        self.assertEqual(f('foo', 10), 'x=foofoo    ')
        x = 'bar'
        self.assertEqual(f(10, 10), 'x=        20')

    def test_locals(self):
        value = 123
        self.assertEqual(f'v:{value}', 'v:123')

    def test_missing_variable(self):
        with self.assertRaises(NameError):
            f'v:{value}'

    def test_missing_format_spec(self):
        class O:
            def __format__(self, spec):
                if not spec:
                    return '*'
                return spec

        self.assertEqual(f'{O():x}', 'x')
        self.assertEqual(f'{O()}', '*')
        self.assertEqual(f'{O():}', '*')

        self.assertEqual(f'{3:}', '3')
        self.assertEqual(f'{3!s:}', '3')

    def test_global(self):
        self.assertEqual(f'g:{a_global}', 'g:global variable')
        self.assertEqual(f'g:{a_global!r}', "g:'global variable'")

        a_local = 'local variable'
        self.assertEqual(f'g:{a_global} l:{a_local}',
                         'g:global variable l:local variable')
        self.assertEqual(f'g:{a_global!r}',
                         "g:'global variable'")
        self.assertEqual(f'g:{a_global} l:{a_local!r}',
                         "g:global variable l:'local variable'")

        self.assertIn("module 'unittest' from", f'{unittest}')

    def test_shadowed_global(self):
        a_global = 'really a local'
        self.assertEqual(f'g:{a_global}', 'g:really a local')
        self.assertEqual(f'g:{a_global!r}', "g:'really a local'")

        a_local = 'local variable'
        self.assertEqual(f'g:{a_global} l:{a_local}',
                         'g:really a local l:local variable')
        self.assertEqual(f'g:{a_global!r}',
                         "g:'really a local'")
        self.assertEqual(f'g:{a_global} l:{a_local!r}',
                         "g:really a local l:'local variable'")

    def test_call(self):
        def foo(x):
            return 'x=' + str(x)

        self.assertEqual(f'{foo(10)}', 'x=10')

    def test_nested_fstrings(self):
        y = 5
        self.assertEqual(f'{f"{0}"*3}', '000')
        self.assertEqual(f'{f"{y}"*3}', '555')

    def test_invalid_string_prefixes(self):
        single_quote_cases = ["fu''",
                             "uf''",
                             "Fu''",
                             "fU''",
                             "Uf''",
                             "uF''",
                             "ufr''",
                             "urf''",
                             "fur''",
                             "fru''",
                             "rfu''",
                             "ruf''",
                             "FUR''",
                             "Fur''",
                             "fb''",
                             "fB''",
                             "Fb''",
                             "FB''",
                             "bf''",
                             "bF''",
                             "Bf''",
                             "BF''",]
        double_quote_cases = [case.replace("'", '"') for case in single_quote_cases]
        self.assertAllRaise(SyntaxError, 'invalid syntax',
                            single_quote_cases + double_quote_cases)

    def test_leading_trailing_spaces(self):
        self.assertEqual(f'{ 3}', '3')
        self.assertEqual(f'{  3}', '3')
        self.assertEqual(f'{3 }', '3')
        self.assertEqual(f'{3  }', '3')

        self.assertEqual(f'expr={ {x: y for x, y in [(1, 2), ]}}',
                         'expr={1: 2}')
        self.assertEqual(f'expr={ {x: y for x, y in [(1, 2), ]} }',
                         'expr={1: 2}')

    def test_not_equal(self):
        # There's a special test for this because there's a special
        #  case in the f-string parser to look for != as not ending an
        #  expression. Normally it would, while looking for !s or !r.

        self.assertEqual(f'{3!=4}', 'True')
        self.assertEqual(f'{3!=4:}', 'True')
        self.assertEqual(f'{3!=4!s}', 'True')
        self.assertEqual(f'{3!=4!s:.3}', 'Tru')

    def test_equal_equal(self):
        # Because an expression ending in = has special meaning,
        # there's a special test for ==. Make sure it works.

        self.assertEqual(f'{0==1}', 'False')

    def test_conversions(self):
        self.assertEqual(f'{3.14:10.10}', '      3.14')
        self.assertEqual(f'{3.14!s:10.10}', '3.14      ')
        self.assertEqual(f'{3.14!r:10.10}', '3.14      ')
        self.assertEqual(f'{3.14!a:10.10}', '3.14      ')

        self.assertEqual(f'{"a"}', 'a')
        self.assertEqual(f'{"a"!r}', "'a'")
        self.assertEqual(f'{"a"!a}', "'a'")

        # Conversions can have trailing whitespace after them since it
        # does not provide any significance
        self.assertEqual(f"{3!s  }", "3")
        self.assertEqual(f'{3.14!s  :10.10}', '3.14      ')

        # Not a conversion.
        self.assertEqual(f'{"a!r"}', "a!r")

        # Not a conversion, but show that ! is allowed in a format spec.
        self.assertEqual(f'{3.14:!<10.10}', '3.14!!!!!!')

        self.assertAllRaise(SyntaxError, "f-string: expecting '}'",
                            ["f'{3!'",
                             "f'{3!s'",
                             "f'{3!g'",
                             ])

        self.assertAllRaise(SyntaxError, 'f-string: missing conversion character',
                            ["f'{3!}'",
                             "f'{3!:'",
                             "f'{3!:}'",
                             ])

        for conv_identifier in 'g', 'A', 'G', 'ä', 'ɐ':
            self.assertAllRaise(SyntaxError,
                                "f-string: invalid conversion character %r: "
                                "expected 's', 'r', or 'a'" % conv_identifier,
                                ["f'{3!" + conv_identifier + "}'"])

        for conv_non_identifier in '3', '!':
            self.assertAllRaise(SyntaxError,
                                "f-string: invalid conversion character",
                                ["f'{3!" + conv_non_identifier + "}'"])

        for conv in ' s', ' s ':
            self.assertAllRaise(SyntaxError,
                                "f-string: conversion type must come right after the"
                                " exclamanation mark",
                                ["f'{3!" + conv + "}'"])

        self.assertAllRaise(SyntaxError,
                            "f-string: invalid conversion character 'ss': "
                            "expected 's', 'r', or 'a'",
                            ["f'{3!ss}'",
                             "f'{3!ss:}'",
                             "f'{3!ss:s}'",
                             ])

    def test_assignment(self):
        self.assertAllRaise(SyntaxError, r'invalid syntax',
                            ["f'' = 3",
                             "f'{0}' = x",
                             "f'{x}' = x",
                             ])

    def test_del(self):
        self.assertAllRaise(SyntaxError, 'invalid syntax',
                            ["del f''",
                             "del '' f''",
                             ])

    def test_mismatched_braces(self):
        self.assertAllRaise(SyntaxError, "f-string: single '}' is not allowed",
                            ["f'{{}'",
                             "f'{{}}}'",
                             "f'}'",
                             "f'x}'",
                             "f'x}x'",
                             r"f'\u007b}'",

                             # Can't have { or } in a format spec.
                             "f'{3:}>10}'",
                             "f'{3:}}>10}'",
                             ])

        self.assertAllRaise(SyntaxError, "f-string: expecting '}'",
                            ["f'{3'",
                             "f'{3!'",
                             "f'{3:'",
                             "f'{3!s'",
                             "f'{3!s:'",
                             "f'{3!s:3'",
                             "f'x{'",
                             "f'x{x'",
                             "f'{x'",
                             "f'{3:s'",
                             "f'{{{'",
                             "f'{{}}{'",
                             "f'{'",
                             "f'{i='",  # See gh-93418.
                             ])

        self.assertAllRaise(SyntaxError,
                            "f-string: expecting a valid expression after '{'",
                            ["f'{3:{{>10}'",
                             ])

        # But these are just normal strings.
        self.assertEqual(f'{"{"}', '{')
        self.assertEqual(f'{"}"}', '}')
        self.assertEqual(f'{3:{"}"}>10}', '}}}}}}}}}3')
        self.assertEqual(f'{2:{"{"}>10}', '{{{{{{{{{2')

    def test_if_conditional(self):
        # There's special logic in compile.c to test if the
        #  conditional for an if (and while) are constants. Exercise
        #  that code.

        def test_fstring(x, expected):
            flag = 0
            if f'{x}':
                flag = 1
            else:
                flag = 2
            self.assertEqual(flag, expected)

        def test_concat_empty(x, expected):
            flag = 0
            if '' f'{x}':
                flag = 1
            else:
                flag = 2
            self.assertEqual(flag, expected)

        def test_concat_non_empty(x, expected):
            flag = 0
            if ' ' f'{x}':
                flag = 1
            else:
                flag = 2
            self.assertEqual(flag, expected)

        test_fstring('', 2)
        test_fstring(' ', 1)

        test_concat_empty('', 2)
        test_concat_empty(' ', 1)

        test_concat_non_empty('', 1)
        test_concat_non_empty(' ', 1)

    def test_empty_format_specifier(self):
        x = 'test'
        self.assertEqual(f'{x}', 'test')
        self.assertEqual(f'{x:}', 'test')
        self.assertEqual(f'{x!s:}', 'test')
        self.assertEqual(f'{x!r:}', "'test'")

    def test_str_format_differences(self):
        d = {'a': 'string',
             0: 'integer',
             }
        a = 0
        self.assertEqual(f'{d[0]}', 'integer')
        self.assertEqual(f'{d["a"]}', 'string')
        self.assertEqual(f'{d[a]}', 'integer')
        self.assertEqual('{d[a]}'.format(d=d), 'string')
        self.assertEqual('{d[0]}'.format(d=d), 'integer')

    def test_errors(self):
        # see issue 26287
        self.assertAllRaise(TypeError, 'unsupported',
                            [r"f'{(lambda: 0):x}'",
                             r"f'{(0,):x}'",
                             ])
        self.assertAllRaise(ValueError, 'Unknown format code',
                            [r"f'{1000:j}'",
                             r"f'{1000:j}'",
                            ])

    def test_filename_in_syntaxerror(self):
        # see issue 38964
        with temp_cwd() as cwd:
            file_path = os.path.join(cwd, 't.py')
            with open(file_path, 'w', encoding="utf-8") as f:
                f.write('f"{a b}"') # This generates a SyntaxError
            _, _, stderr = assert_python_failure(file_path,
                                                 PYTHONIOENCODING='ascii')
        self.assertIn(file_path.encode('ascii', 'backslashreplace'), stderr)

    def test_loop(self):
        for i in range(1000):
            self.assertEqual(f'i:{i}', 'i:' + str(i))

    def test_dict(self):
        d = {'"': 'dquote',
             "'": 'squote',
             'foo': 'bar',
             }
        self.assertEqual(f'''{d["'"]}''', 'squote')
        self.assertEqual(f"""{d['"']}""", 'dquote')

        self.assertEqual(f'{d["foo"]}', 'bar')
        self.assertEqual(f"{d['foo']}", 'bar')

    def test_backslash_char(self):
        # Check eval of a backslash followed by a control char.
        # See bpo-30682: this used to raise an assert in pydebug mode.
        self.assertEqual(eval('f"\\\n"'), '')
        self.assertEqual(eval('f"\\\r"'), '')

    def test_debug_conversion(self):
        x = 'A string'
        self.assertEqual(f'{x=}', 'x=' + repr(x))
        self.assertEqual(f'{x =}', 'x =' + repr(x))
        self.assertEqual(f'{x=!s}', 'x=' + str(x))
        self.assertEqual(f'{x=!r}', 'x=' + repr(x))
        self.assertEqual(f'{x=!a}', 'x=' + ascii(x))

        x = 2.71828
        self.assertEqual(f'{x=:.2f}', 'x=' + format(x, '.2f'))
        self.assertEqual(f'{x=:}', 'x=' + format(x, ''))
        self.assertEqual(f'{x=!r:^20}', 'x=' + format(repr(x), '^20'))
        self.assertEqual(f'{x=!s:^20}', 'x=' + format(str(x), '^20'))
        self.assertEqual(f'{x=!a:^20}', 'x=' + format(ascii(x), '^20'))

        x = 9
        self.assertEqual(f'{3*x+15=}', '3*x+15=42')

        # There is code in ast.c that deals with non-ascii expression values.  So,
        # use a unicode identifier to trigger that.
        tenπ = 31.4
        self.assertEqual(f'{tenπ=:.2f}', 'tenπ=31.40')

        # Also test with Unicode in non-identifiers.
        self.assertEqual(f'{"Σ"=}', '"Σ"=\'Σ\'')

        # Make sure nested fstrings still work.
        self.assertEqual(f'{f"{3.1415=:.1f}":*^20}', '*****3.1415=3.1*****')

        # Make sure text before and after an expression with = works
        # correctly.
        pi = 'π'
        self.assertEqual(f'alpha α {pi=} ω omega', "alpha α pi='π' ω omega")

        # Check multi-line expressions.
        self.assertEqual(f'''{
3
=}''', '\n3\n=3')

        # Since = is handled specially, make sure all existing uses of
        # it still work.

        self.assertEqual(f'{0==1}', 'False')
        self.assertEqual(f'{0!=1}', 'True')
        self.assertEqual(f'{0<=1}', 'True')
        self.assertEqual(f'{0>=1}', 'False')
        self.assertEqual(f'{(x:="5")}', '5')
        self.assertEqual(x, '5')
        self.assertEqual(f'{(x:=5)}', '5')
        self.assertEqual(x, 5)
        self.assertEqual(f'{"="}', '=')

        x = 20
        # This isn't an assignment expression, it's 'x', with a format
        # spec of '=10'.  See test_walrus: you need to use parens.
        self.assertEqual(f'{x:=10}', '        20')

        # Test named function parameters, to make sure '=' parsing works
        # there.
        def f(a):
            nonlocal x
            oldx = x
            x = a
            return oldx
        x = 0
        self.assertEqual(f'{f(a="3=")}', '0')
        self.assertEqual(x, '3=')
        self.assertEqual(f'{f(a=4)}', '3=')
        self.assertEqual(x, 4)

        # Check debug expressions in format spec
        y = 20
        self.assertEqual(f"{2:{y=}}", "yyyyyyyyyyyyyyyyyyy2")
        self.assertEqual(f"{datetime.datetime.now():h1{y=}h2{y=}h3{y=}}",
                         'h1y=20h2y=20h3y=20')

        # Make sure __format__ is being called.
        class C:
            def __format__(self, s):
                return f'FORMAT-{s}'
            def __repr__(self):
                return 'REPR'

        self.assertEqual(f'{C()=}', 'C()=REPR')
        self.assertEqual(f'{C()=!r}', 'C()=REPR')
        self.assertEqual(f'{C()=:}', 'C()=FORMAT-')
        self.assertEqual(f'{C()=: }', 'C()=FORMAT- ')
        self.assertEqual(f'{C()=:x}', 'C()=FORMAT-x')
        self.assertEqual(f'{C()=!r:*^20}', 'C()=********REPR********')
        self.assertEqual(f"{C():{20=}}", 'FORMAT-20=20')

        self.assertRaises(SyntaxError, eval, "f'{C=]'")


        # Make sure leading and following text works.
        x = 'foo'
        self.assertEqual(f'X{x=}Y', 'Xx='+repr(x)+'Y')

        # Make sure whitespace around the = works.
        self.assertEqual(f'X{x  =}Y', 'Xx  ='+repr(x)+'Y')
        self.assertEqual(f'X{x=  }Y', 'Xx=  '+repr(x)+'Y')
        self.assertEqual(f'X{x  =  }Y', 'Xx  =  '+repr(x)+'Y')
        self.assertEqual(f"sadsd {1 + 1 =  :{1 + 1:1d}f}", "sadsd 1 + 1 =  2.000000")

        self.assertEqual(f"{1+2 = # my comment
  }", '1+2 = \n  3')

        # These next lines contains tabs.  Backslash escapes don't
        # work in f-strings.
        # patchcheck doesn't like these tabs.  So the only way to test
        # this will be to dynamically created and exec the f-strings.  But
        # that's such a hassle I'll save it for another day.  For now, convert
        # the tabs to spaces just to shut up patchcheck.
        #self.assertEqual(f'X{x =}Y', 'Xx\t='+repr(x)+'Y')
        #self.assertEqual(f'X{x =       }Y', 'Xx\t=\t'+repr(x)+'Y')

    def test_walrus(self):
        x = 20
        # This isn't an assignment expression, it's 'x', with a format
        # spec of '=10'.
        self.assertEqual(f'{x:=10}', '        20')

        # This is an assignment expression, which requires parens.
        self.assertEqual(f'{(x:=10)}', '10')
        self.assertEqual(x, 10)

    def test_invalid_syntax_error_message(self):
        with self.assertRaisesRegex(SyntaxError,
                                    "f-string: expecting '=', or '!', or ':', or '}'"):
            compile("f'{a $ b}'", "?", "exec")

    def test_with_two_commas_in_format_specifier(self):
        error_msg = re.escape("Cannot specify ',' with ','.")
        with self.assertRaisesRegex(ValueError, error_msg):
            f'{1:,,}'

    def test_with_two_underscore_in_format_specifier(self):
        error_msg = re.escape("Cannot specify '_' with '_'.")
        with self.assertRaisesRegex(ValueError, error_msg):
            f'{1:__}'

    def test_with_a_commas_and_an_underscore_in_format_specifier(self):
        error_msg = re.escape("Cannot specify both ',' and '_'.")
        with self.assertRaisesRegex(ValueError, error_msg):
            f'{1:,_}'

    def test_with_an_underscore_and_a_comma_in_format_specifier(self):
        error_msg = re.escape("Cannot specify both ',' and '_'.")
        with self.assertRaisesRegex(ValueError, error_msg):
            f'{1:_,}'

    def test_syntax_error_for_starred_expressions(self):
        with self.assertRaisesRegex(SyntaxError, "can't use starred expression here"):
            compile("f'{*a}'", "?", "exec")

        with self.assertRaisesRegex(SyntaxError,
                                    "f-string: expecting a valid expression after '{'"):
            compile("f'{**a}'", "?", "exec")

    def test_not_closing_quotes(self):
        self.assertAllRaise(SyntaxError, "unterminated f-string literal", ['f"', "f'"])
        self.assertAllRaise(SyntaxError, "unterminated triple-quoted f-string literal",
                            ['f"""', "f'''"])
        # Ensure that the errors are reported at the correct line number.
        data = '''\
x = 1 + 1
y = 2 + 2
z = f"""
sdfjnsdfjsdf
sdfsdfs{1+
2} dfigdf {3+
4}sdufsd""
'''
        try:
            compile(data, "?", "exec")
        except SyntaxError as e:
            self.assertEqual(e.text, 'z = f"""')
            self.assertEqual(e.lineno, 3)
    def test_syntax_error_after_debug(self):
        self.assertAllRaise(SyntaxError, "f-string: expecting a valid expression after '{'",
                            [
                                "f'{1=}{;'",
                                "f'{1=}{+;'",
                                "f'{1=}{2}{;'",
                                "f'{1=}{3}{;'",
                            ])
        self.assertAllRaise(SyntaxError, "f-string: expecting '=', or '!', or ':', or '}'",
                            [
                                "f'{1=}{1;'",
                                "f'{1=}{1;}'",
                            ])

    def test_debug_in_file(self):
        with temp_cwd():
            script = 'script.py'
            with open('script.py', 'w') as f:
                f.write(f"""\
print(f'''{{
3
=}}''')""")

            _, stdout, _ = assert_python_ok(script)
        self.assertEqual(stdout.decode('utf-8').strip().replace('\r\n', '\n').replace('\r', '\n'),
                         "3\n=3")

    def test_syntax_warning_infinite_recursion_in_file(self):
        with temp_cwd():
            script = 'script.py'
            with open(script, 'w') as f:
                f.write(r"print(f'\{1}')")

            _, stdout, stderr = assert_python_ok(script)
            self.assertIn(rb'\1', stdout)
            self.assertEqual(len(stderr.strip().splitlines()), 2)

    def test_fstring_without_formatting_bytecode(self):
        # f-string without any formatting should emit the same bytecode
        # as a normal string. See gh-99606.
        def get_code(s):
            return [(i.opname, i.oparg) for i in dis.get_instructions(s)]

        for s in ["", "some string"]:
            self.assertEqual(get_code(f"'{s}'"), get_code(f"f'{s}'"))

if __name__ == '__main__':
    unittest.main()