[Python-ideas] Compact repr operator (i.e., __short_repr__)

[Chris Barker]

On Mon, Feb 8, 2016 at 3:36 PM, Mahmoud Hashemi <mahmoud at hatnote.com> wrote:

> The motivation is that there are many cases where producing the full,
> round-trippable repr is possible, but would take up significant resources
> or be too huge to be useful for human consumption.
>

numpy as realized this, and produced a __repr__ (and __str__) that
truncates:

In [*26*]: len(arr)

Out[*26*]: 100000

In [*27*]: repr(arr)

Out[*27*]: 'array([  0.00000000e+00,   1.00001000e-02,   2.00002000e-02,
...,\n         9.99980000e+02,   9.99990000e+02,   1.00000000e+03])'

I"m not sure that a full-sized repr is ever useful, so this seems fine to
me.

I wonder how often anyone actually counts on eval(repr(obj)) == obj ?

In short, I don't see that this would be all that useful.

-CHB






> The built-in [reprlib module][1] certainly shows there's an interest for
> many built-in types, and I think arguably that same functionality is
> desirable for user types.
>
> As mentioned in the subject a possible API could be:
>
> class ValueObject(object):
>     def __init__(self, content):
>         self.content = content
>
>     def __repr__(self):
>         return '%s(%r)' % (self.__class__.__name__, self.content)
>
>     def __short_repr__(self, size=None, depth=None):
>         # TODO: should interpretation of size/depth be casual or strict?
>         if size and len(self.content) > size:
>             short_content = self.content[:size] + '...'
>         else:
>             pass  # TODO: could just return normal repr possibly
>         return '<%s content=%r)' % (self.__class__.__name__, short_content)
>
> Without something like this, there's no way to ask an object if it's repr
> is of manageable length, or how its repr could be meaningfully shortened.
> Usually I just chop out the middle and add an ellipsis, but as for the time
> spent generating that middle, I'll never get those cycles back.
>
> Anyways, thanks for your attention, and happy Monday to all!
>
> Mahmoud
> https://github.com/mahmoud
> https://twitter.com/mhashemi
> http://sedimental.org
>
> [1]: https://docs.python.org/2/library/functions.html#func-repr
> [2]: https://docs.python.org/3.4/library/reprlib.html
>
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