create a decorator for adding default keyword arguments to a function

[mwhansen]

The typical usage of this decorator would be to be applied above a
:obj:cached_method or :obj:cached_function decorator so that
the correct cached object is returned.

CC: @mwhansen @jasongrout

Component: misc

Author: Tim Dumol

Reviewer: Mike Hansen

Merged: sage-4.4.2.alpha0

Issue created by migration from https://trac.sagemath.org/ticket/5405

[nthiery]

comment:1

Attachment: trac_5405.patch.gz

Hi Mike!

I am not so sure about the name, although I can't propose much better than
default_values, or set_default_values.

Could it be generalized to handle both positional and non positional arguments?

I'd suggest to have the doc by starting with what the thing actually does, followed by the typical usage.
Speaking of which: could you add an example of this typical usage? (it was not clear to me).

[nthiery]

comment:3

Oops, should have set the subject to needs work. Done.

[TimDumol]

comment:5

Sorry if I don't get this right, but doesn't functools.partial already fulfill this purpose?

[jasongrout]

comment:6

Do you mean something like this?

from functools import partial

def partial_dec(*args, **kwds):
    def p(f):
        return partial(f,*args,**kwds)
    return p
    
@partial_dec(b=2)
def f(a,b):
    return 10*a+b

f(4)

[TimDumol]

comment:7

Actually I meant something like this:

from functools import partial

@partial(partial, b=4)
def f(a,b):
    return 10*a + b

f(4)

[jasongrout]

comment:8

Cute. Very nice!

[jasongrout]

comment:9

So now can you use @wraps or something so that g? works correctly below?

from functools import partial, wraps

@partial(partial, b=4)
def g(a,b):
    """Docs"""
    return 10*a + b

g?

[TimDumol]

comment:10

This works, but it certainly isn't obvious:

from functools import partial, wraps

@partial(lambda x: wraps(x)(partial(partial, b = 4))(x))
def g(a,b):
    """Docs"""
    return 10*a + b

print(g(5))

g?

[jasongrout]

comment:11

and at that point, I'd say

@default_keywords...
def g...

is nicer. However, one might use partial in the above decorator. I think our discussion is evidence for the usefulness of the idea on this ticket.