Implement `Signature.__repr__`

[cool-RR]

BPO	20378
Nosy	@terryjreedy, @cool-RR, @1st1

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/1st1'
closed_at = <Date 2014-03-27.16:42:21.087>
created_at = <Date 2014-01-24.14:05:52.658>
labels = ['library']
title = 'Implement `Signature.__repr__`'
updated_at = <Date 2014-03-27.16:42:21.085>
user = 'https://github.com/cool-RR'

bugs.python.org fields:

activity = <Date 2014-03-27.16:42:21.085>
actor = 'python-dev'
assignee = 'yselivanov'
closed = True
closed_date = <Date 2014-03-27.16:42:21.087>
closer = 'python-dev'
components = ['Library (Lib)']
creation = <Date 2014-01-24.14:05:52.658>
creator = 'cool-RR'
dependencies = []
files = []
hgrepos = []
issue_num = 20378
keywords = []
message_count = 5.0
messages = ['209112', '209114', '209455', '209456', '214966']
nosy_count = 4.0
nosy_names = ['terry.reedy', 'cool-RR', 'python-dev', 'yselivanov']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue20378'
versions = ['Python 3.5']

[terryjreedy]

Signature.__repr__ already exits. It is inherited from object. So you must be proposing to override the inherited method. For what purpose? With what outcome?

Without reading the signature PEP, I believe the current difference between str and repr is intentional, not accidental. Example:
>>> repr(s)
'<inspect.Signature object at 0x02E7BC08>'
>>> str(s)
'(self, a)'

If so, this issue should be closed unless you can provide an excellent reason to break code the expects the current behavior.

[cool-RR]

My impression is that the __repr__ method of any object is intended to describe that object, hopefully in a succinct way, possibly in a REPL-friendly way (like list.__repr__ for example) but if not then at least human-friendly. This is for easy introspection. When I come across a Signature object in the shell, I want to immediately get a good feel for what it contains without exploring vars(sig) manully.

If you have a Signature object, why not have its __repr__ return something like '<Signature f: alpha, beta=3, *args, **kwargs>`? This would do an awesome job at helping me understand what kind of signature object I'm looking at.

[1st1]

Ram, yes, I agree. Something like '<Signature f: alpha, beta=3, *args, **kwargs>' should work.

[cool-RR]

If you'd like to expand this issue's scope to all the objects related to Signature, I think that'll be good. All objects need good introspection strings.

[python-dev]

New changeset 3f9a81297b39 by Yury Selivanov in branch 'default':
inspect.signature: Improve repr of Signature and Parameter. Closes bpo-20378
http://hg.python.org/cpython/rev/3f9a81297b39