[Python-ideas] Reprs of classes and functions

[Steven D'Aprano]

On Wed, Feb 25, 2015 at 10:12:03AM +0200, Serhiy Storchaka 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.

Do you mean like this?

repr(int)
=> 'int'

repr(int.from_bytes)
=> 'int.from_bytes'

repr(open)
=> 'open'

repr(collections.Counter)
=> 'collections.Counter'

repr(collections.Counter.fromkeys)
=> 'collections.Counter.fromkeys'

repr(collections.namedtuple)
=> 'collections.namedtuple'


-1 on that idea.

The suggested repr gives no clue as to what kind of object they are. Are 
they functions, methods, classes, some kind of Enum-like constant or 
something special like None? That hurts the usefulness of object reprs 
at the interactive interpreter. And it leads to weirdness like this:


def spam(x):
    if not isinstance(x, int):
        raise TypeError('expected int, got %r' % x)


# current behaviour
spam(int)
=> TypeError: expected int, got <class 'int'>

# proposed behaviour
spam(int)
=> TypeError: expected int, got int


As for them being evaluable, I don't think that's terribly useful. Do 
you have a use-case for that?

I'm not saying that it will never be useful, but I don't think it is 
useful enough to make up for the loss of human-readable information (the 
type of the object). Being able to eval(repr(instance)) is sometimes 
handy, but I don't think eval(repr(type_or_function)) is useful.



-- 
Steve