import ast import types import decimal import unittest 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_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, '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(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, "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' { } '", # 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'", ]) 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') 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, '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') 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_invalid_expressions(self): self.assertAllRaise(SyntaxError, 'invalid syntax', [r"f'{a[4)}'", r"f'{a(4]}'", ]) 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_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') if __name__ == '__main__': unittest.main()