# cython: language_level=3

# mode: run

# tag: allow_unknown_names, f_strings, pep498

import ast

import types

import decimal

import unittest

import contextlib

import sys

IS_PY2 = sys.version_info[0] < 3

IS_PY26 = sys.version_info[:2] < (2, 7)

from Cython.Build.Inline import cython_inline

from Cython.TestUtils import CythonTest

from Cython.Compiler.Errors import CompileError, hold_errors, release_errors, error_stack, held_errors

def cy_eval(s, **kwargs):

    return cython_inline('return ' + s, force=True, **kwargs)

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(CythonTest):

    def assertAllRaise(self, exception_type, regex, error_strings):

        for str in error_strings:

            hold_errors()

            if exception_type is SyntaxError:

                try:

                    self.fragment(str)

                except CompileError:

                    assert True

                else:

                    assert held_errors(), "Invalid Cython code failed to raise SyntaxError: %r" % str

                finally:

                    release_errors(ignore=True)

            else:

                try:

                    cython_inline(str, quiet=True)

                except exception_type:

                    assert True

                else:

                    assert False, "Invalid Cython code failed to raise %s: %r" % (exception_type, str)

                finally:

                    if error_stack:

                        release_errors(ignore=True)

    if IS_PY2:

        def assertEqual(self, first, second, msg=None):

            # strip u'' string prefixes in Py2

            if first != second and isinstance(first, unicode):

                stripped_first = first.replace("u'", "'").replace('u"', '"')

                if stripped_first == second:

                    first = stripped_first

                elif stripped_first.decode('unicode_escape') == second:

                    first = stripped_first.decode('unicode_escape')

            super(TestCase, self).assertEqual(first, second, msg)

        if IS_PY26:

            @contextlib.contextmanager

            def assertRaises(self, exc):

                try:

                    yield

                except exc:

                    pass

                else:

                    assert False, "exception '%s' not raised" % exc

            def assertIn(self, value, collection):

                self.assertTrue(value in collection)

    def test__format__lookup(self):

        if IS_PY26:

            return

        elif IS_PY2:

            raise unittest.SkipTest("Py3-only")

        # 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_docstring(self):

        def f():

            f'''Not a docstring'''

        self.assertTrue(f.__doc__ is None)

        def g():

            '''Not a docstring''' \

            f''

        self.assertTrue(g.__doc__ is None)

    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, 'f-string: mismatched',

                            ["f'{((}'",

                             ])

    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'{#}'",

                             "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(cy_eval(build_fstr(i), x=x, width=width), (x+' ')*i)

        # Test concatenating 2 largs fstrings.

        self.assertEqual(cy_eval(build_fstr(255)*3, x=x, width=width), (x+' ')*(255*3))  # CPython uses 255*256

        s = build_fstr(253, '{x:{width}} ')

        self.assertEqual(cy_eval(s, x=x, width=width), (x+' ')*254)

        # Test lots of expressions and constants, concatenated.

        s = "f'{1}' 'x' 'y'" * 1024

        self.assertEqual(cy_eval(s, x=x, width=width), '1xy' * 1024)

    def test_format_specifier_expressions(self):

        width = 10

        precision = 4

        value = decimal.Decimal('12.34567')

        if not IS_PY26:

            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, "invalid syntax",

                            [# Invalid syntax inside a nested spec.

                             "f'{4:{/5}}'",

                             ])

        # CYTHON: The nesting restriction seems rather arbitrary. Ignoring it for now and instead test that it works.

        if not IS_PY26:

            self.assertEqual(f'result: {value:{width:{0}}.{precision:1}}', 'result:      12.35')

        #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, 'invalid character in identifier',

                            ["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, 'invalid syntax',

                            ["f'{,}'",

                             "f'{,}'",  # this is (,), which is an error

                             ])

        self.assertAllRaise(SyntaxError, "f-string: expecting '}'",

                            ["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 = cy_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'")

        if not IS_PY2:

            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, 'unexpected EOF while parsing',

                            ["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}'

        g = fn(4)

        self.assertEqual(next(g), 8)

    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):

        self.assertAllRaise(SyntaxError, 'unexpected EOF while parsing',

                            ["fu''",

                             "uf''",

                             "Fu''",

                             "fU''",

                             "Uf''",

                             "uF''",

                             "ufr''",

                             "urf''",

                             "fur''",

                             "fru''",

                             "rfu''",

                             "ruf''",

                             "FUR''",

                             "Fur''",

                             "fb''",

                             "fB''",

                             "Fb''",

                             "FB''",

                             "bf''",

                             "bF''",

                             "Bf''",

                             "BF''",

                             ])

    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_conversions(self):

        self.assertEqual(f'{3.14:10.10}', '      3.14')

        if not IS_PY26:

            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(CompileError, 'invalid syntax',   # CPython raises SyntaxError

                            ["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_invalid_expressions(self):

        self.assertAllRaise(SyntaxError, 'invalid syntax',

                            [r"f'{a[4)}'",

                             r"f'{a(4]}'",

                            ])

    def test_errors(self):

        # see issue 26287

        exc = ValueError if sys.version_info < (3, 4) else TypeError

        self.assertAllRaise(exc, '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_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(cy_eval('f"\\\n"'), '')

        self.assertEqual(cy_eval('f"\\\r"'), '')

if __name__ == '__main__':

    unittest.main()