[issue6081] str.format_from_mapping()
Eric Smith e...@trueblade.com added the comment: Updated patch which adds tests and minimal docs. Named changed to format_map. I'll commit this before 3.2b1 unless I hear a complaint. -- keywords: +easy, needs review resolution: - accepted Added file: http://bugs.python.org/file19482/issue6081-1.diff ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue6081 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue6081] str.format_from_mapping()
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[issue6081] str.format_from_mapping()
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[issue6081] str.format_from_mapping()
Raymond Hettinger rhettin...@users.sourceforge.net added the comment: This can be done for Py3.2. It completes needed functionality for string formatting which is something we all want to take hold and is necessary for the 3.x series to succeed. -- versions: +Python 3.2 -Python 3.3 ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue6081 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue6081] str.format_from_mapping()
Eric Smith e...@trueblade.com added the comment: I'll work on cleaning this up for 3.2. Any comments on the name of the method? -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue6081 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue6081] str.format_from_mapping()
Terry J. Reedy tjre...@udel.edu added the comment: I understand now that new methods, as opposed to changed methods, are allowed. I agree with Eric that this seems more like a convinience rather than absolute necessity, and that the doc should be augmented. The doc for vformat (which I admit I had not noticed before) says it is exposed just for this case: vformat(format_string, args, kwargs) This function does the actual work of formatting. It is exposed as a separate function for cases where you want to pass in a predefined dictionary of arguments, rather than unpacking and repacking the dictionary as individual arguments using the *args and **kwds syntax. 'Dictionary' should be replaced with 'mapping'. string.Formatter.format is documented as just a wrapper that calls vformat(). Is the same effectively true of str.format also? If .format_map (I prefer shorted names) is added as a convenience str method, particularly for matching current %-formatting use, I think it should take just one parameter, mapping. I presume it could implemented as a wrapper for .vformat (or whatever internal function .vformat calls). str.format_map(map) == string.Format.vformat(formstring, (), map) More complicated, mixed cases can use the explict lookup with map arg. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue6081 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue6081] str.format_from_mapping()
Terry J. Reedy tjre...@udel.edu added the comment: I believe this is covered by the PEP3003 3.2 change moratorium. -- nosy: +terry.reedy versions: +Python 3.3 -Python 2.7, Python 3.2 ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue6081 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue6081] str.format_from_mapping()
Eric Smith e...@trueblade.com added the comment:
It occurs to me that Raymond's use case could be satisfied using existing
Python, by slightly changing the format string. After all, str.format()
supports mapping lookup already:
$ ./python.exe
Python 2.6.5+ (release26-maint:79421, Mar 25 2010, 08:51:39)
[GCC 4.2.1 (Apple Inc. build 5646) (dot 1)] on darwin
Type help, copyright, credits or license for more information.
class Default(dict):
... def __missing__(self, key):
... return key
...
s = '{m[name]} was born in {m[country]}'
s.format(m=Default(name='Guido'))
'Guido was born in country'
Considering that, maybe the best thing is to do nothing. Or maybe update the
documentation with this example.
Plus, you could mix and match this with *args as you'd like.
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[issue6081] str.format_from_mapping()
Filip Gruszczyński grusz...@gmail.com added the comment: I have created a new patch, that should be satisfying now. There is help (though it is quite small, I tried to mimic those that were already in unicode.c) and tests. Right now format_using_mapping is called like this: format_using_mapping(mapping, *args) where mapping is a subscriptible object, that will be pushed to kwargs and the following args are used just like in normal format. This should be as similar to the normal format as possible. There are also tests, including usage presented in the ticket. -- Added file: http://bugs.python.org/file16632/6081_2.diff ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue6081 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue6081] str.format_from_mapping()
Eric Smith e...@trueblade.com added the comment:
I'm not sure I'm wild about the *args parameter. Calling Fred the 0-th
parameter here seems non-intuitive:
My name is {0}.format_using_mapping({}, 'Fred')
If you're going to have *args, why not **kwargs and then merge/update the
dicts? I'm being facetious, but I think even having *args is feature creep.
I think it's time to ask about this on python-dev. I'd vote for not using
*args. It can always be added in the future if it's seen as a hole in the API.
--
stage: test needed - patch review
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[issue6081] str.format_from_mapping()
Eric Smith e...@trueblade.com added the comment: I believe this patch fixes the issue. Tests and documentation are still needed, of course. -- Added file: http://bugs.python.org/file16585/issue6081.diff ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue6081 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue6081] str.format_from_mapping()
Eric Smith e...@trueblade.com added the comment: Added a comment to explain the change. -- Added file: http://bugs.python.org/file16586/issue6081.diff ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue6081 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue6081] str.format_from_mapping()
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[issue6081] str.format_from_mapping()
Filip Gruszczyński grusz...@gmail.com added the comment: Could you point me, where to add tests and documentation? I would happily add those. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue6081 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue6081] str.format_from_mapping()
Eric Smith e...@trueblade.com added the comment: http://docs.python.org/library/stdtypes.html#str.format, for starters. This is in Doc/library/stdtypes.rst. For tests, probably in Lib/test/test_unicode.py. I'm not sure if we should add this to 2.7 (or even 3.2, for that matter), but if so, we should start by patching trunk and then porting to py3k. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue6081 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue6081] str.format_from_mapping()
Filip Gruszczyński grusz...@gmail.com added the comment:
Ok, unfortunately this code won't work for certain tests. Take those:
self.assertEqual(My name is {0}.format('Fred'), My name is Fred)
We pass only one argument, which is a dict and this won't satisfy such test. We
need to think about a different way of passing those arguments there. We can do
one of two thins:
* the last argument of args tuple would be an object that can be subscripted
for format values
* keyword with above object
I believe the second version is more explicit and therefore better.
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[issue6081] str.format_from_mapping()
Filip Gruszczyński grusz...@gmail.com added the comment:
I have created a small patch, that adds method that formats using a dict. It's
the first time I have written anything in python implementation, so I would
very appreciate any advice. Change allows the following:
m = Mapping(a='b')
'{a} {c}'.format_using_mapping(m)
'b c'
--
keywords: +patch
nosy: +gruszczy
Added file: http://bugs.python.org/file16576/6081_1.patch
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[issue6081] str.format_from_mapping()
Ezio Melotti ezio.melo...@gmail.com added the comment: Thanks for the patch. It would be nice if you could include unit tests too. -- priority: - normal stage: - test needed ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue6081 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue6081] str.format_from_mapping()
R. David Murray rdmur...@bitdance.com added the comment: I don't think this patch satisfies Raymond's request. It is explicitly checking for a __missing__ attribute, but Raymond was talking about a more general facility whereby you can pass in an arbitrary object that implements the mapping interface. Using the __missing__ facility was just an example of why this would be useful. -- nosy: +r.david.murray ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue6081 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue6081] str.format_from_mapping()
Eric Smith e...@trueblade.com added the comment: I agree with David. Although it's not clear to my why the code doesn't just work with the addition of do_string_format_using_mapping and without the other code. It's possible the existing code is too dict-specific and should be calling a more generic PyObject interface, like PyMapping_GetItemString instead of PyDict_GetItem. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue6081 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue6081] str.format_from_mapping()
Filip Gruszczyński grusz...@gmail.com added the comment: My first intention was simply to push mapping from args to kwargs, just like Eric suggested, but that didn't help with __missing__, only with accepting a dict instead of pushing keyword arguments. I didn't like explicitly asking for __missing__ either, but since I have little knowledge of what should be called, I didn't know what to use. I too believe something else the PyDict_GetItem should be called, something that would take care of __missing__ and other possibilities (I don't know what exactly and really would like to know what these are) internally. I am going to check, whether PyMapping_GetItemString is going to help. But can this really be called on a dict (or a subclass of dict)? What about retrieving getitem method from the given object and simply calling it? Wouldn't that do the trick? -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue6081 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue6081] str.format_from_mapping()
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[issue6081] str.format_from_mapping()
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[issue6081] str.format_from_mapping()
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[issue6081] str.format_from_mapping()
Eric Smith e...@trueblade.com added the comment: I think this would be useful. I don't fee terribly strongly about it, but I think I'd like the name str.format_using_mapping(). When I initially saw this, I thought from the name it was creating a format object (whatever that would be) from a mapping object. -- components: +Interpreter Core ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue6081 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue6081] str.format_from_mapping()
Changes by Eric Smith e...@trueblade.com: -- nosy: +eric.smith ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue6081 ___ ___ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue6081] str.format_from_mapping()
New submission from Raymond Hettinger rhettin...@users.sourceforge.net:
The old % formatting allowed arbitrary mappings:
class Default(dict):
... def __missing__(self, key):
... return key
...
s = '%(name)s was born in %(country)s'
s % Default(name='Guido')
'Guido was born in country'
But the new str.format() demands mappings be first converted to a
regular dict using **kwargs, so something like the above is not possible.
s = '{name} was born in {country}'
s.format(**Default(name='Guido'))
Traceback (most recent call last):
File pyshell#27, line 1, in module
s.format(**Default(name='Guido'))
KeyError: 'country'
There is a work-around using string.vformat() but it is obscure and awkward:
import string
string.Formatter().vformat(s, (), Default(name='Guido'))
'Guido was born in country'
Instead, it would be better to offer an alternate method:
s.format_from_mapping(Default(name='Guido'))
'Guido was born in country'
--
messages: 88173
nosy: rhettinger
severity: normal
status: open
title: str.format_from_mapping()
type: feature request
versions: Python 2.7, Python 3.2
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