def c2py(plural):
    """Gets a C expression as used in PO files for plural forms and returns a
    Python lambda function that implements an equivalent expression.
    """
    # Security check, allow only the "n" identifier
    try:
        from cStringIO import StringIO
    except ImportError:
        from StringIO import StringIO
    import token, tokenize
    tokens = tokenize.generate_tokens(StringIO(plural).readline)
    try:
        danger = [x for x in tokens if x[0] == token.NAME and x[1] != 'n']
    except tokenize.TokenError:
        raise ValueError, \
              'plural forms expression error, maybe unbalanced parenthesis'
    else:
        if danger:
            raise ValueError, 'plural forms expression could be dangerous'

    # Replace some C operators by their Python equivalents
    plural = plural.replace('&&', ' and ')
    plural = plural.replace('||', ' or ')

    expr = re.compile(r'\!([^=])')
    plural = expr.sub(' not \\1', plural)

    # Regular expression and replacement function used to transform
    # "a?b:c" to "test(a,b,c)".
    expr = re.compile(r'(.*?)\?(.*?):(.*)')
    def repl(x):
        return "test(%s, %s, %s)" % (x.group(1), x.group(2),
                                     expr.sub(repl, x.group(3)))

    # Code to transform the plural expression, taking care of parentheses
    stack = ['']
    for c in plural:
        if c == '(':
            stack.append('')
        elif c == ')':
            if len(stack) == 1:
                # Actually, we never reach this code, because unbalanced
                # parentheses get caught in the security check at the
                # beginning.
                raise ValueError, 'unbalanced parenthesis in plural form'
            s = expr.sub(repl, stack.pop())
            stack[-1] += '(%s)' % s
        else:
            stack[-1] += c
    plural = expr.sub(repl, stack.pop())

    return eval(plural % 'lambda n: int(%s)')
dataset/ETHPy150Open grow/grow/grow/pods/storage/gettext_storage.py/c2py/swapped operands of `%`