| msg195263 - (view) |
Author: Andrew Svetlov (asvetlov) *  |
Date: 2013-08-15 17:10 |
| I think this is a bug. Can be reproduced on all Pythons (from 2.6 to 3.4a). Maybe should be fixed for 3.4 only as backward incompatible change. |
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| msg195268 - (view) |
Author: R. David Murray (r.david.murray) * |
Date: 2013-08-15 18:14 |
| What is it that doesn't fail? The expression in the title is the beginning of a triple quoted string with no closing triple quote. If you mean '' % [1] not falling, it has been that way forever (well, python2.4 is as far back as I can test), so if it is deemed worth changing it certainly should not be backported. I suspect it is some consequence of the C level similarities between lists and dicts, since '' % {} is supposed to not produce an error. |
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| msg195269 - (view) |
Author: STINNER Victor (vstinner) * |
Date: 2013-08-15 18:18 |
| I don't understand why str % list and str % dict behaves differently than str % int: >>> 'abc' % [1] 'abc' >>> 'abc' % ([1],) Traceback (most recent call last): File "", line 1, in TypeError: not all arguments converted during string formatting >>> 'abc' % 1 Traceback (most recent call last): File "", line 1, in TypeError: not all arguments converted during string formatting >>> 'abc' % {1:2} 'abc' >>> 'abc' % ({1:2},) Traceback (most recent call last): File "", line 1, in TypeError: not all arguments converted during string formatting |
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| msg195272 - (view) |
Author: R. David Murray (r.david.murray) * |
Date: 2013-08-15 18:34 |
| haypo: str % dict is a feature: >>> "%(a)s" % {'a': 1, 'b': 2} '1' |
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| msg195273 - (view) |
Author: Andrew Svetlov (asvetlov) * |
Date: 2013-08-15 18:38 |
| For dict it is correct from my perspective. "" % {'a': 'b'} tries to substitute format specs like "%(a)s" and does nothing if spec is not present. But list case like "" % [1] confuse me. |
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| msg195281 - (view) |
Author: R. David Murray (r.david.murray) * |
Date: 2013-08-15 19:48 |
| Yes, I suspect you are right that that is a bug...and a long standing one :) |
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| msg195309 - (view) |
Author: Eric V. Smith (eric.smith) * |
Date: 2013-08-16 04:04 |
| Objects/unicodeobject.c has this, at line 14316: if (PyMapping_Check(args) && !PyTuple_Check(args) && !PyUnicode_Check(args)) ctx.dict = args; else ctx.dict = NULL; and later at line 14348: if (ctx.argidx < ctx.arglen && !ctx.dict) { PyErr_SetString(PyExc_TypeError, "not all arguments converted during string formatting"); goto onError; } Because list now returns true for PyMapping_Check, this code thinks the list is a dict and skips the error. There's some discussion of PyMapping_Check in issue 5945. |
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| msg195326 - (view) |
Author: R. David Murray (r.david.murray) * |
Date: 2013-08-16 13:24 |
| Hmm. The linked issue says the PyMappingCheck behavior is new in Python3, but this problem exists in Python2 (back to 2.4 at least) as well. Perhaps it is a different bug in Python2. |
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| msg195329 - (view) |
Author: Eric V. Smith (eric.smith) * |
Date: 2013-08-16 13:31 |
| The code looks basically the same in 2.7, and there PyMapping_Check looks for __getitem__, so maybe issue 5945 is just incorrect in its analysis. In any event, I'm not sure this is worth fixing. There are lots of little corner cases that could be broken. |
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| msg195629 - (view) |
Author: Giacomo Alzetta (bakuriu) |
Date: 2013-08-19 13:04 |
| Note that the documentation for formatting with %, found here: http://docs.python.org/2/library/stdtypes.html#string-formatting-operations, states: """ If format requires a single argument, values may be a single non-tuple object. [5] Otherwise, values must be a tuple with exactly the number of items specified by the format string, or a single mapping object (for example, a dictionary).""" Note how it explicitly states that in an expression: format % value there are two different cases: - If format contains *exactly one* format specifier, then value can be any non-tuple item and it will be formatted as is. Otherwise, value MUST be either tuple or a mapping. In your example '' contains 0 format specifiers, hence you MUST use either a tuple or a dict. Any other object triggers "undefined behaviour"(in particular depending on whether the object define __geitem__ or not the formatting might or might not raise an exception etc.) AFAIK only few people know this, hence changing the code could potentially break a lot of code for apparently no reason. Since people should start to move to str.format instead of % this wart may not be worth fixing. |
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| msg195656 - (view) |
Author: Serhiy Storchaka (serhiy.storchaka) * |
Date: 2013-08-19 18:52 |
| > Since people should start to move to str.format instead of % this wart may not be worth fixing. >>> ''.format_map([1]) '' However I agree that this is not worth fixing. |
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| msg196719 - (view) |
Author: Andrew Svetlov (asvetlov) * |
Date: 2013-09-01 12:39 |
| Ok. Close as won't fix. Please reopen if needed. |
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