Issue #28563: Fixed possible DoS and arbitrary code execution when handle
plural form selections in the gettext module. The expression parser now supports exact syntax supported by GNU gettext.
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commit
eb20fcae14
168
Lib/gettext.py
168
Lib/gettext.py
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@ -59,55 +59,139 @@ __all__ = ['NullTranslations', 'GNUTranslations', 'Catalog',
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_default_localedir = os.path.join(sys.base_prefix, 'share', 'locale')
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# Expression parsing for plural form selection.
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#
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# The gettext library supports a small subset of C syntax. The only
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# incompatible difference is that integer literals starting with zero are
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# decimal.
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#
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# https://www.gnu.org/software/gettext/manual/gettext.html#Plural-forms
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# http://git.savannah.gnu.org/cgit/gettext.git/tree/gettext-runtime/intl/plural.y
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_token_pattern = re.compile(r"""
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(?P<WHITESPACES>[ \t]+) | # spaces and horizontal tabs
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(?P<NUMBER>[0-9]+\b) | # decimal integer
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(?P<NAME>n\b) | # only n is allowed
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(?P<PARENTHESIS>[()]) |
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(?P<OPERATOR>[-*/%+?:]|[><!]=?|==|&&|\|\|) | # !, *, /, %, +, -, <, >,
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# <=, >=, ==, !=, &&, ||,
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# ? :
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# unary and bitwise ops
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# not allowed
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(?P<INVALID>\w+|.) # invalid token
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""", re.VERBOSE|re.DOTALL)
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def _tokenize(plural):
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for mo in re.finditer(_token_pattern, plural):
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kind = mo.lastgroup
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if kind == 'WHITESPACES':
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continue
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value = mo.group(kind)
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if kind == 'INVALID':
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raise ValueError('invalid token in plural form: %s' % value)
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yield value
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yield ''
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def _error(value):
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if value:
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return ValueError('unexpected token in plural form: %s' % value)
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else:
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return ValueError('unexpected end of plural form')
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_binary_ops = (
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('||',),
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('&&',),
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('==', '!='),
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('<', '>', '<=', '>='),
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('+', '-'),
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('*', '/', '%'),
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)
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_binary_ops = {op: i for i, ops in enumerate(_binary_ops, 1) for op in ops}
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_c2py_ops = {'||': 'or', '&&': 'and', '/': '//'}
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def _parse(tokens, priority=-1):
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result = ''
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nexttok = next(tokens)
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while nexttok == '!':
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result += 'not '
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nexttok = next(tokens)
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if nexttok == '(':
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sub, nexttok = _parse(tokens)
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result = '%s(%s)' % (result, sub)
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if nexttok != ')':
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raise ValueError('unbalanced parenthesis in plural form')
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elif nexttok == 'n':
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result = '%s%s' % (result, nexttok)
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else:
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try:
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value = int(nexttok, 10)
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except ValueError:
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raise _error(nexttok) from None
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result = '%s%d' % (result, value)
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nexttok = next(tokens)
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j = 100
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while nexttok in _binary_ops:
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i = _binary_ops[nexttok]
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if i < priority:
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break
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# Break chained comparisons
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if i in (3, 4) and j in (3, 4): # '==', '!=', '<', '>', '<=', '>='
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result = '(%s)' % result
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# Replace some C operators by their Python equivalents
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op = _c2py_ops.get(nexttok, nexttok)
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right, nexttok = _parse(tokens, i + 1)
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result = '%s %s %s' % (result, op, right)
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j = i
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if j == priority == 4: # '<', '>', '<=', '>='
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result = '(%s)' % result
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if nexttok == '?' and priority <= 0:
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if_true, nexttok = _parse(tokens, 0)
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if nexttok != ':':
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raise _error(nexttok)
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if_false, nexttok = _parse(tokens)
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result = '%s if %s else %s' % (if_true, result, if_false)
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if priority == 0:
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result = '(%s)' % result
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return result, nexttok
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def c2py(plural):
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"""Gets a C expression as used in PO files for plural forms and returns a
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Python lambda function that implements an equivalent expression.
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Python function that implements an equivalent expression.
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"""
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# Security check, allow only the "n" identifier
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import token, tokenize
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tokens = tokenize.generate_tokens(io.StringIO(plural).readline)
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if len(plural) > 1000:
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raise ValueError('plural form expression is too long')
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try:
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danger = [x for x in tokens if x[0] == token.NAME and x[1] != 'n']
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except tokenize.TokenError:
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raise ValueError('plural forms expression error, maybe unbalanced parenthesis')
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else:
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if danger:
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raise ValueError('plural forms expression could be dangerous')
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result, nexttok = _parse(_tokenize(plural))
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if nexttok:
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raise _error(nexttok)
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# Replace some C operators by their Python equivalents
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plural = plural.replace('&&', ' and ')
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plural = plural.replace('||', ' or ')
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expr = re.compile(r'\!([^=])')
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plural = expr.sub(' not \\1', plural)
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# Regular expression and replacement function used to transform
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# "a?b:c" to "b if a else c".
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expr = re.compile(r'(.*?)\?(.*?):(.*)')
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def repl(x):
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return "(%s if %s else %s)" % (x.group(2), x.group(1),
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expr.sub(repl, x.group(3)))
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# Code to transform the plural expression, taking care of parentheses
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stack = ['']
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for c in plural:
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if c == '(':
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stack.append('')
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elif c == ')':
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if len(stack) == 1:
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# Actually, we never reach this code, because unbalanced
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# parentheses get caught in the security check at the
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# beginning.
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raise ValueError('unbalanced parenthesis in plural form')
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s = expr.sub(repl, stack.pop())
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stack[-1] += '(%s)' % s
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else:
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stack[-1] += c
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plural = expr.sub(repl, stack.pop())
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return eval('lambda n: int(%s)' % plural)
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depth = 0
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for c in result:
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if c == '(':
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depth += 1
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if depth > 20:
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# Python compiler limit is about 90.
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# The most complex example has 2.
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raise ValueError('plural form expression is too complex')
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elif c == ')':
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depth -= 1
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ns = {}
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exec('''if True:
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def func(n):
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if not isinstance(n, int):
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raise ValueError('Plural value must be an integer.')
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return int(%s)
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''' % result, ns)
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return ns['func']
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except RecursionError:
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# Recursion error can be raised in _parse() or exec().
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raise ValueError('plural form expression is too complex')
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def _expand_lang(loc):
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@ -306,7 +306,9 @@ class PluralFormsTestCase(GettextBaseTest):
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x = t.ngettext('There is %s file', 'There are %s files', 2)
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eq(x, 'Hay %s ficheros')
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def test_hu(self):
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# Examples from http://www.gnu.org/software/gettext/manual/gettext.html
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def test_ja(self):
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eq = self.assertEqual
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f = gettext.c2py('0')
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s = ''.join([ str(f(x)) for x in range(200) ])
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@ -324,6 +326,12 @@ class PluralFormsTestCase(GettextBaseTest):
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s = ''.join([ str(f(x)) for x in range(200) ])
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eq(s, "00111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111")
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def test_lv(self):
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eq = self.assertEqual
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f = gettext.c2py('n%10==1 && n%100!=11 ? 0 : n != 0 ? 1 : 2')
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s = ''.join([ str(f(x)) for x in range(200) ])
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eq(s, "20111111111111111111101111111110111111111011111111101111111110111111111011111111101111111110111111111011111111111111111110111111111011111111101111111110111111111011111111101111111110111111111011111111")
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def test_gd(self):
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eq = self.assertEqual
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f = gettext.c2py('n==1 ? 0 : n==2 ? 1 : 2')
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@ -337,6 +345,12 @@ class PluralFormsTestCase(GettextBaseTest):
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s = ''.join([ str(f(x)) for x in range(200) ])
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eq(s, "20122222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222")
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def test_ro(self):
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eq = self.assertEqual
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f = gettext.c2py('n==1 ? 0 : (n==0 || (n%100 > 0 && n%100 < 20)) ? 1 : 2')
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s = ''.join([ str(f(x)) for x in range(200) ])
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eq(s, "10111111111111111111222222222222222222222222222222222222222222222222222222222222222222222222222222222111111111111111111122222222222222222222222222222222222222222222222222222222222222222222222222222222")
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def test_lt(self):
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eq = self.assertEqual
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f = gettext.c2py('n%10==1 && n%100!=11 ? 0 : n%10>=2 && (n%100<10 || n%100>=20) ? 1 : 2')
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@ -349,6 +363,12 @@ class PluralFormsTestCase(GettextBaseTest):
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s = ''.join([ str(f(x)) for x in range(200) ])
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eq(s, "20111222222222222222201112222220111222222011122222201112222220111222222011122222201112222220111222222011122222222222222220111222222011122222201112222220111222222011122222201112222220111222222011122222")
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def test_cs(self):
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eq = self.assertEqual
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f = gettext.c2py('(n==1) ? 0 : (n>=2 && n<=4) ? 1 : 2')
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s = ''.join([ str(f(x)) for x in range(200) ])
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eq(s, "20111222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222")
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def test_pl(self):
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eq = self.assertEqual
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f = gettext.c2py('n==1 ? 0 : n%10>=2 && n%10<=4 && (n%100<10 || n%100>=20) ? 1 : 2')
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@ -361,10 +381,73 @@ class PluralFormsTestCase(GettextBaseTest):
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s = ''.join([ str(f(x)) for x in range(200) ])
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eq(s, "30122333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333012233333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333")
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def test_ar(self):
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eq = self.assertEqual
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f = gettext.c2py('n==0 ? 0 : n==1 ? 1 : n==2 ? 2 : n%100>=3 && n%100<=10 ? 3 : n%100>=11 ? 4 : 5')
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s = ''.join([ str(f(x)) for x in range(200) ])
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eq(s, "01233333333444444444444444444444444444444444444444444444444444444444444444444444444444444444444444445553333333344444444444444444444444444444444444444444444444444444444444444444444444444444444444444444")
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def test_security(self):
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raises = self.assertRaises
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# Test for a dangerous expression
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raises(ValueError, gettext.c2py, "os.chmod('/etc/passwd',0777)")
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# issue28563
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raises(ValueError, gettext.c2py, '"(eval(foo) && ""')
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raises(ValueError, gettext.c2py, 'f"{os.system(\'sh\')}"')
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# Maximum recursion depth exceeded during compilation
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raises(ValueError, gettext.c2py, 'n+'*10000 + 'n')
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self.assertEqual(gettext.c2py('n+'*100 + 'n')(1), 101)
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# MemoryError during compilation
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raises(ValueError, gettext.c2py, '('*100 + 'n' + ')'*100)
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# Maximum recursion depth exceeded in C to Python translator
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raises(ValueError, gettext.c2py, '('*10000 + 'n' + ')'*10000)
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self.assertEqual(gettext.c2py('('*20 + 'n' + ')'*20)(1), 1)
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def test_chained_comparison(self):
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# C doesn't chain comparison as Python so 2 == 2 == 2 gets different results
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f = gettext.c2py('n == n == n')
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self.assertEqual(''.join(str(f(x)) for x in range(3)), '010')
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f = gettext.c2py('1 < n == n')
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self.assertEqual(''.join(str(f(x)) for x in range(3)), '100')
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f = gettext.c2py('n == n < 2')
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self.assertEqual(''.join(str(f(x)) for x in range(3)), '010')
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f = gettext.c2py('0 < n < 2')
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self.assertEqual(''.join(str(f(x)) for x in range(3)), '111')
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def test_decimal_number(self):
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self.assertEqual(gettext.c2py('0123')(1), 123)
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def test_invalid_syntax(self):
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invalid_expressions = [
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'x>1', '(n>1', 'n>1)', '42**42**42', '0xa', '1.0', '1e2',
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'n>0x1', '+n', '-n', 'n()', 'n(1)', '1+', 'nn', 'n n',
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]
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for expr in invalid_expressions:
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with self.assertRaises(ValueError):
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gettext.c2py(expr)
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def test_nested_condition_operator(self):
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self.assertEqual(gettext.c2py('n?1?2:3:4')(0), 4)
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self.assertEqual(gettext.c2py('n?1?2:3:4')(1), 2)
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self.assertEqual(gettext.c2py('n?1:3?4:5')(0), 4)
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self.assertEqual(gettext.c2py('n?1:3?4:5')(1), 1)
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def test_division(self):
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f = gettext.c2py('2/n*3')
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self.assertEqual(f(1), 6)
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self.assertEqual(f(2), 3)
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self.assertEqual(f(3), 0)
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self.assertEqual(f(-1), -6)
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self.assertRaises(ZeroDivisionError, f, 0)
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def test_plural_number(self):
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f = gettext.c2py('1')
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self.assertEqual(f(1), 1)
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self.assertRaises(ValueError, f, 1.0)
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self.assertRaises(ValueError, f, '1')
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self.assertRaises(ValueError, f, [])
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self.assertRaises(ValueError, f, object())
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class GNUTranslationParsingTest(GettextBaseTest):
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def test_plural_form_error_issue17898(self):
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