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bpo-45995: add "z" format specifer to coerce negative 0 to zero (GH-30049)

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Add "z" format specifier to coerce negative 0 to zero.

See https://github.com/python/cpython/issues/90153 (originally https://bugs.python.org/issue45995) for discussion.
This covers `str.format()` and f-strings.  Old-style string interpolation is not supported.

Co-authored-by: Mark Dickinson <dickinsm@gmail.com>
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John Belmonte 2022-04-11 23:34:18 +09:00 • committed by GitHub
parent dd207a6ac5
commit b0b836b20c
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16 changed files with 368 additions and 43 deletions
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74
Lib/test/test_format.py
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@ -546,6 +546,80 @@ class FormatTest(unittest.TestCase):
with self.assertRaisesRegex(ValueError, str_err):
"{a:%ЫйЯЧ}".format(a='a')
def test_negative_zero(self):
## default behavior
self.assertEqual(f"{-0.:.1f}", "-0.0")
self.assertEqual(f"{-.01:.1f}", "-0.0")
self.assertEqual(f"{-0:.1f}", "0.0") # integers do not distinguish -0
## z sign option
self.assertEqual(f"{0.:z.1f}", "0.0")
self.assertEqual(f"{0.:z6.1f}", " 0.0")
self.assertEqual(f"{-1.:z6.1f}", " -1.0")
self.assertEqual(f"{-0.:z.1f}", "0.0")
self.assertEqual(f"{.01:z.1f}", "0.0")
self.assertEqual(f"{-0:z.1f}", "0.0") # z is allowed for integer input
self.assertEqual(f"{-.01:z.1f}", "0.0")
self.assertEqual(f"{0.:z.2f}", "0.00")
self.assertEqual(f"{-0.:z.2f}", "0.00")
self.assertEqual(f"{.001:z.2f}", "0.00")
self.assertEqual(f"{-.001:z.2f}", "0.00")
self.assertEqual(f"{0.:z.1e}", "0.0e+00")
self.assertEqual(f"{-0.:z.1e}", "0.0e+00")
self.assertEqual(f"{0.:z.1E}", "0.0E+00")
self.assertEqual(f"{-0.:z.1E}", "0.0E+00")
self.assertEqual(f"{-0.001:z.2e}", "-1.00e-03") # tests for mishandled
# rounding
self.assertEqual(f"{-0.001:z.2g}", "-0.001")
self.assertEqual(f"{-0.001:z.2%}", "-0.10%")
self.assertEqual(f"{-00000.000001:z.1f}", "0.0")
self.assertEqual(f"{-00000.:z.1f}", "0.0")
self.assertEqual(f"{-.0000000000:z.1f}", "0.0")
self.assertEqual(f"{-00000.000001:z.2f}", "0.00")
self.assertEqual(f"{-00000.:z.2f}", "0.00")
self.assertEqual(f"{-.0000000000:z.2f}", "0.00")
self.assertEqual(f"{.09:z.1f}", "0.1")
self.assertEqual(f"{-.09:z.1f}", "-0.1")
self.assertEqual(f"{-0.: z.0f}", " 0")
self.assertEqual(f"{-0.:+z.0f}", "+0")
self.assertEqual(f"{-0.:-z.0f}", "0")
self.assertEqual(f"{-1.: z.0f}", "-1")
self.assertEqual(f"{-1.:+z.0f}", "-1")
self.assertEqual(f"{-1.:-z.0f}", "-1")
self.assertEqual(f"{0.j:z.1f}", "0.0+0.0j")
self.assertEqual(f"{-0.j:z.1f}", "0.0+0.0j")
self.assertEqual(f"{.01j:z.1f}", "0.0+0.0j")
self.assertEqual(f"{-.01j:z.1f}", "0.0+0.0j")
self.assertEqual(f"{-0.:z>6.1f}", "zz-0.0") # test fill, esp. 'z' fill
self.assertEqual(f"{-0.:z>z6.1f}", "zzz0.0")
self.assertEqual(f"{-0.:x>z6.1f}", "xxx0.0")
self.assertEqual(f"{-0.:🖤>z6.1f}", "🖤🖤🖤0.0") # multi-byte fill char
def test_specifier_z_error(self):
error_msg = re.compile("Invalid format specifier '.*z.*'")
with self.assertRaisesRegex(ValueError, error_msg):
f"{0:z+f}" # wrong position
with self.assertRaisesRegex(ValueError, error_msg):
f"{0:fz}" # wrong position
error_msg = re.escape("Negative zero coercion (z) not allowed")
with self.assertRaisesRegex(ValueError, error_msg):
f"{0:zd}" # can't apply to int presentation type
with self.assertRaisesRegex(ValueError, error_msg):
f"{'x':zs}" # can't apply to string
error_msg = re.escape("unsupported format character 'z'")
with self.assertRaisesRegex(ValueError, error_msg):
"%z.1f" % 0 # not allowed in old style string interpolation
if __name__ == "__main__":
unittest.main()