cpython/Lib/test/test_fstring.py

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# -*- 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 os
import re
import types
import decimal
import unittest
from test.support.os_helper import temp_cwd
from test.support.script_helper import assert_python_failure
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):
"""Duplicate expression
NOTE: this is currently broken, always sets location of the first
expression.
"""
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, 3) # FIXME: this is wrong
self.assertEqual(binop.left.col_offset, 3) # FIXME: this is wrong
self.assertEqual(binop.right.col_offset, 7) # FIXME: this is wrong
# 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, 3) # FIXME: this is wrong
self.assertEqual(binop.left.col_offset, 3) # FIXME: this is wrong
self.assertEqual(binop.right.col_offset, 7) # FIXME: this is wrong
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, 3)
self.assertEqual(t.body[1].value.values[2].lineno, 3)
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, 0)
self.assertEqual(t.body[1].value.values[1].col_offset, 0)
self.assertEqual(t.body[1].value.values[2].col_offset, 0)
# 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, 4)
self.assertEqual(binop.left.col_offset, 4)
self.assertEqual(binop.right.col_offset, 7)
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, 'f-string: unterminated string',
[r"""f'{"x'""",
r"""f'{"x}'""",
r"""f'{("x'""",
r"""f'{("x}'""",
])
def test_mismatched_parens(self):
self.assertAllRaise(SyntaxError, r"f-string: closing parenthesis '\}' "
r"does not match opening parenthesis '\('",
["f'{((}'",
])
self.assertAllRaise(SyntaxError, r"f-string: closing parenthesis '\)' "
r"does not match opening parenthesis '\['",
["f'{a[4)}'",
])
self.assertAllRaise(SyntaxError, r"f-string: closing parenthesis '\]' "
r"does not match opening parenthesis '\('",
["f'{a(4]}'",
])
self.assertAllRaise(SyntaxError, r"f-string: closing parenthesis '\}' "
r"does not match opening parenthesis '\['",
["f'{a[4}'",
])
self.assertAllRaise(SyntaxError, r"f-string: closing parenthesis '\}' "
r"does not match opening parenthesis '\('",
["f'{a(4}'",
])
self.assertRaises(SyntaxError, eval, "f'{" + "("*500 + "}'")
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'' '', '')
self.assertAllRaise(SyntaxError, "f-string: 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, "f-string expression part cannot include '#'",
["f'{1#}'", # error because the expression becomes "(1#)"
"f'{3(#)}'",
"f'{#}'",
])
self.assertAllRaise(SyntaxError, r"f-string: unmatched '\)'",
["f'{)#}'", # When wrapped in parens, this becomes
# '()#)'. Make sure that doesn't compile.
])
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.assertAllRaise(SyntaxError, "f-string: expecting '}'",
["""f'{"s"!r{":10"}}'""",
# This looks like a nested format spec.
])
self.assertAllRaise(SyntaxError, "f-string: invalid syntax",
[# Invalid syntax inside a nested spec.
"f'{4:{/5}}'",
])
self.assertAllRaise(SyntaxError, "f-string: expressions nested too deeply",
[# Can't nest format specifiers.
"f'result: {value:{width:{0}}.{precision:1}}'",
])
self.assertAllRaise(SyntaxError, 'f-string: invalid conversion character',
[# No expansion inside conversion or for
# the : or ! itself.
"""f'{"s"!{"r"}}'""",
])
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: empty expression not allowed',
["f'{}'",
"f'{ }'"
"f' {} '",
"f'{!r}'",
"f'{ !r}'",
"f'{10:{ }}'",
"f' { } '",
# The Python parser ignores also the following
# whitespace characters in additional to a space.
"f'''{\t\f\r\n}'''",
# Catch the empty expression before the
# invalid conversion.
"f'{!x}'",
"f'{ !xr}'",
"f'{!x:}'",
"f'{!x:a}'",
"f'{ !xr:}'",
"f'{ !xr:a}'",
"f'{!}'",
"f'{:}'",
# We find the empty expression before the
# missing closing brace.
"f'{!'",
"f'{!s:'",
"f'{:'",
"f'{:x'",
])
# 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,)')
# Add these because when an expression is evaluated, parens
# are added around it. But we shouldn't go from an invalid
# expression to a valid one. The added parens are just
# supposed to allow whitespace (including newlines).
self.assertAllRaise(SyntaxError, 'f-string: invalid syntax',
["f'{,}'",
"f'{,}'", # this is (,), which is an error
])
self.assertAllRaise(SyntaxError, r"f-string: unmatched '\)'",
["f'{3)+(4}'",
])
self.assertAllRaise(SyntaxError, 'EOL while scanning string literal',
["f'{\n}'",
])
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(DeprecationWarning): # invalid escape sequence
value = eval(r"f'\{6*7}'")
self.assertEqual(value, '\\42')
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{GREEK CAPITAL LETTER DELTA'",
# Here are the non-f-string versions,
# which should give the same errors.
r"'\N'",
r"'\N{'",
r"'\N{GREEK CAPITAL LETTER DELTA'",
])
def test_no_backslashes_in_expression_part(self):
self.assertAllRaise(SyntaxError, 'f-string expression part cannot include a backslash',
[r"f'{\'a\'}'",
r"f'{\t3}'",
r"f'{\}'",
r"rf'{\'a\'}'",
r"rf'{\t3}'",
r"rf'{\}'",
r"""rf'{"\N{LEFT CURLY BRACKET}"}'""",
r"f'{\n}'",
])
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
self.assertAllRaise(SyntaxError, 'f-string: invalid syntax',
["f'{lambda x:x}'",
])
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, 'unexpected EOF while parsing',
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'")
# 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: invalid conversion character',
["f'{3!g}'",
"f'{3!A}'",
"f'{3!3}'",
"f'{3!G}'",
"f'{3!!}'",
"f'{3!:}'",
"f'{3! s}'", # no space before conversion char
])
self.assertAllRaise(SyntaxError, "f-string: expecting '}'",
["f'{x!s{y}}'",
"f'{3!ss}'",
"f'{3!ss:}'",
"f'{3!ss:s}'",
])
def test_assignment(self):
self.assertAllRaise(SyntaxError, '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:{{>10}'",
"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'{'",
])
# 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') 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)
# 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.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')
# 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: invalid syntax"):
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:_,}'
if __name__ == '__main__':
unittest.main()