Method test_format_specifier_expressions

Lib/test/test_fstring.py:814–845

(self)

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

        self.assertAllRaise(SyntaxError, "f-string: expecting ':' or '}'",
                            ["""f'{"s"!r{":10"}}'""",
                             # This looks like a nested format spec.
                             ])

        self.assertAllRaise(SyntaxError,
                            "f-string: expecting a valid expression after '{'",
                            [# Invalid syntax inside a nested spec.
                             "f'{4:{/5}}'",
                             ])

        self.assertAllRaise(SyntaxError, 'f-string: invalid conversion character',
                            [# No expansion inside conversion or for
                             #  the : or ! itself.
                             """f'{"s"!{"r"}}'""",
                             ])

    def test_custom_format_specifier(self):
        class CustomFormat: