[Python-ideas] Reprs of classes and functions

[Robert Collins]

I plan on committing http://bugs.python.org/issue13224 tomorrowish
(the patch is a little stale and I want to poke around some to be sure
its ok).

If anyone objects please follow up in the issue.

-Rob

On 26 February 2015 at 16:28, Guido van Rossum <guido at python.org> wrote:
> I didn't read all that, but my use case is that for typing.py (PEP 484) I
> want "nice" reprs for higher-order classes, and if str(int) returned just
> 'int' it would be much simpler to e.g. make the str() or repr() of
> Optional[int] return "Optional[int]". I've sort of solved this already in
> https://github.com/ambv/typehinting/blob/master/prototyping/typing.py, but
> it would still be nice if I didn't have to work so hard at it.
>
> On Wed, Feb 25, 2015 at 5:41 PM, Andrew Barnert
> <abarnert at yahoo.com.dmarc.invalid> wrote:
>>
>> On Feb 25, 2015, at 8:21, Guido van Rossum <guido at python.org> wrote:
>>
>> A variant I've often wanted is to make str() return the "clean" type only
>> (e.g. 'int') while leaving repr() alone -- this would address most problems
>> Steven brought up.
>>
>>
>> On further thought, I'm not sure backward compatibility can be dismissed.
>> Surely code shouldn't care about the str of a callable, right? But yeah,
>> sometimes it might care, if it's, say, a reflective framework for bridging
>> or debugging or similar.
>>
>> I once wrote a library that exposed Python objects over AppleEvents. I
>> needed to know all the bound methods of the object. For pure-Python objects,
>> this is easy, but for builtin/extension objects, the bound methods
>> constructed from both slot-wrapper and method-descriptor are of type
>> method-wrapper. (The bug turned up when an obscure corner of our code that
>> tried lxml, cElementTree, then ElementTree was run on a 2.x system without
>> lxml installed, something we'd left out of the test matrix for that module.)
>>
>> When you print out the method, it's obvious what type it is. But how do
>> you deal with it programmatically? Despite what the docs say,
>> method-descriptor does not return true for either isbuiltin or isroutine. In
>> fact, nothing in inspect is much help. And the type isn't in types. Printing
>> out the method, it's dead obvious what it is.
>>
>> As it turned out, callable(x) and (hasattr(x, 'im_self') or hasattr(x,
>> '__self__')) was good enough for my particular use case, at least in all
>> Python interpreters/versions we supported (it even works in PyPy with CPyExt
>> extension types and an early version of NumPyPy). But what would a good
>> general solution be?
>>
>> I think dynamically constructing the type from int().__add__ and then
>> verifying that all extension types in all interpreters and versions I care
>> about pass isinstance(that) unless they look like pure-Python bound methods
>> might be the best way. And even if I did resort to using the string
>> representation, I'd probably use the repr rather than the str, and I'd
>> probably look at type(x) rather than x itself. But still, I can imagine
>> someone deciding "whatever I do is going to be hacky, because there's no
>> non-hacky way to get this information, so I might as well go with the
>> simplest hack that's worked on every CPython and PyPy version from 2.2 to
>> today" and use "... or str(x).startswith('<method-wrapper')".
>>
>>
>> On Wed, Feb 25, 2015 at 12:12 AM, Serhiy Storchaka <storchaka at gmail.com>
>> wrote:
>>>
>>> This idea is already casually mentioned, but sank deep into the threads
>>> of the discussion. Raise it up.
>>>
>>> Currently reprs of classes and functions look as:
>>>
>>> >>> int
>>> <class 'int'>
>>> >>> int.from_bytes
>>> <built-in method from_bytes of type object at 0x826cf60>
>>> >>> open
>>> <built-in function open>
>>> >>> import collections
>>> >>> collections.Counter
>>> <class 'collections.Counter'>
>>> >>> collections.Counter.fromkeys
>>> <bound method Counter.fromkeys of <class 'collections.Counter'>>
>>> >>> collections.namedtuple
>>> <function namedtuple at 0xb6fc4adc>
>>>
>>> What if change default reprs of classes and functions to just full
>>> qualified name __module__ + '.' + __qualname__ (or just __qualname__ if
>>> __module__ is builtins)? This will look more neatly. And such reprs are
>>> evaluable.
>>>
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>>
>>
>>
>>
>> --
>> --Guido van Rossum (python.org/~guido)
>>
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>
>
>
>
> --
> --Guido van Rossum (python.org/~guido)
>
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-- 
Robert Collins <rbtcollins at hp.com>
Distinguished Technologist
HP Converged Cloud