[autodoc] please avoid evaluating default function arguments

[mitya57]

Currently if Sphinx encounters a function like this:

def age(self, now=datetime.datetime.utcnow()):

It generates output like this:

age(now=datetime.datetime(2016, 8, 5, 7, 33, 8, 845335))

I think it is confusing and should be avoided.
(Originally reported at Debian #833820.)

[peterjc]

This looks like a duplicate of #759 to me.

[tgandor]

@mitya57 - this example is cool, however the function is wrong ;) The default now would be only evaluated at time of function definition.

[mitya57]

I know, I said exactly that in the linked downstream bug.

[tk0miya]

I made a super experimental extension for this.
https://gist.github.com/4279adc2d6ff4da52ea73c18cfdd229a

I'd like to know side effect to enable this by default. So it might be needed to add a new option to enable it.

[tk0miya]

Will be fixed by #8771. Closing.