`inspect.get_source(lambda)` improvement

[dg-pb]

Feature or enhancement

Proposal:

l1, v1, v2 = (lambda x: x), 1, 2
print(inspect.getsource(l1)[:-1])
# l1, v1, v2 = (lambda x: x), 1, 2

As the request is for the source of lambda, it might be convenient to extract only the lambda substring, not the whole line.

l1, l2 = (lambda x: x), (lambda x: (x[0] + 1) / 2)
print(inspect.getsource(l1)[:-1])
# l1, l2 = (lambda x: x), (lambda x: (x[0] + 1) / 2)

It might also be nicer to extract the substring of lambda that was requested in case of more than 1 lambda?

Has this already been discussed elsewhere?

No response given

Links to previous discussion of this feature:

No response

[terryjreedy]

This would require getsource to special case functions with __name__ == '<lambda>' by doing special-case analysis of the retrieved line or lines. In the first case, it would find just one lambda expression, so could assume that is was the proper one. In the second case, it would have to compile both expressions and see which one has bytecode that matches that of the anonymous function it was asked to find the source of.

I think that this is asking too much, especially in the 2nd case. If one wants to bind a function object to a name, PEP 8 recommends that one use the proper statement, a named function statement, which starts with def. For the first example:

def l1(x): return x
v1, v2 = 1, 2

and similarly for the 2nd example. The makes the entire line the proper response, as for other getsource objects.

Don't be disappointed if this is closed as "won't fix". If you follow PEP 8 and only use anonymous lambda expressions, you will never directly ask for the source thereof.

[dg-pb]

I am more interested to find out if it would be useful / makes sense to have it work this way in the first place.

If yes, I might be able to work something sensible out.
If not, then oh well.

[dg-pb]

Ah by the way, this is how I ended up with this.

I wanted to improve __repr__ of an object that has predicate argument, where very common predicate is a lambda.

Instead of having:
foo(pred=<function <lambda> at 0x120812840>)
Thought it might be nice to make it:
foo(pred=lambda x: x**2)
Then reached out for inspect.getsource finding it not being able to do what I need robustly.

[dg-pb]

If anyone needs current getsource functionality, then getsourcelines does that, thus getsource could in theory be made to do better what it supposedly should?

Don't be disappointed

I think I have made this work for myself (might need to revisit if it is suitable for stdlib though), thus am not too fussed about this. Just thought it could be a nice tweak for stdlib.