[Python-ideas] Reprs of classes and functions

[Guido van Rossum]

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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