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Issue 5237, Allow auto-numbered replacement fields in str.format() strings.

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For simple uses for str.format(), this makes the typing easier. Hopfully this
will help in the adoption of str.format().

For example:
'The {} is {}'.format('sky', 'blue')

You can mix and matcth auto-numbering and named replacement fields:
'The {} is {color}'.format('sky', color='blue')

But you can't mix and match auto-numbering and specified numbering:
'The {0} is {}'.format('sky', 'blue')
ValueError: cannot switch from manual field specification to automatic field numbering

Will port to 3.1.
This commit is contained in:
Eric Smith 2009-03-14 11:57:26 +00:00
parent feeafff052
commit 6f42edb682
4 changed files with 198 additions and 50 deletions
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36
Lib/test/test_str.py
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@ -347,9 +347,9 @@ class StrTest(
self.assertRaises(ValueError, "{0!}".format, 0)
self.assertRaises(ValueError, "{0!rs}".format, 0)
self.assertRaises(ValueError, "{!}".format)
self.assertRaises(ValueError, "{:}".format)
self.assertRaises(ValueError, "{:s}".format)
self.assertRaises(ValueError, "{}".format)
self.assertRaises(IndexError, "{:}".format)
self.assertRaises(IndexError, "{:s}".format)
self.assertRaises(IndexError, "{}".format)
# can't have a replacement on the field name portion
self.assertRaises(TypeError, '{0[{1}]}'.format, 'abcdefg', 4)
@ -364,6 +364,36 @@ class StrTest(
self.assertRaises(ValueError, format, "", "-")
self.assertRaises(ValueError, "{0:=s}".format, '')
def test_format_auto_numbering(self):
class C:
def __init__(self, x=100):
self._x = x
def __format__(self, spec):
return spec
self.assertEqual('{}'.format(10), '10')
self.assertEqual('{:5}'.format('s'), 's ')
self.assertEqual('{!r}'.format('s'), "'s'")
self.assertEqual('{._x}'.format(C(10)), '10')
self.assertEqual('{[1]}'.format([1, 2]), '2')
self.assertEqual('{[a]}'.format({'a':4, 'b':2}), '4')
self.assertEqual('a{}b{}c'.format(0, 1), 'a0b1c')
self.assertEqual('a{:{}}b'.format('x', '^10'), 'a x b')
self.assertEqual('a{:{}x}b'.format(20, '#'), 'a0x14b')
# can't mix and match numbering and auto-numbering
self.assertRaises(ValueError, '{}{1}'.format, 1, 2)
self.assertRaises(ValueError, '{1}{}'.format, 1, 2)
self.assertRaises(ValueError, '{:{1}}'.format, 1, 2)
self.assertRaises(ValueError, '{0:{}}'.format, 1, 2)
# can mix and match auto-numbering and named
self.assertEqual('{f}{}'.format(4, f='test'), 'test4')
self.assertEqual('{}{f}'.format(4, f='test'), '4test')
self.assertEqual('{:{f}}{g}{}'.format(1, 3, g='g', f=2), ' 1g3')
self.assertEqual('{f:{}}{}{g}'.format(2, 4, f=1, g='g'), ' 14g')
def test_buffer_is_readonly(self):
self.assertRaises(TypeError, sys.stdin.readinto, b"")