Support partials and tz.curry

[tlambert03]

This implements support for functions wrapped in functools.partial. closes #315

There is a slight "catch" ... which is really due to the way that partial handles signatures when providing positional vs keyword arguments. Take this example

    def some_func(x: int, y: str) -> str:
        return y + str(x)

    wdg1 = magicgui(partial(some_func, 1))  # first position
    wdg2 = magicgui(partial(some_func, y='hi'))  # second kwarg

wdg1 will look like this:

and wdg2 will look like this

they both behave like the corresponding partials. but wdg2 shows the widget for y, whereas wdg doesn't show x

To avoid that behavior automatically, we'd need to do a little special casing. It's possible, but prefer to leave to another PR

[codecov]

Codecov Report

Merging #316 (f8b1f42) into main (aa226dc) will increase coverage by 0.06%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #316      +/-   ##
==========================================
+ Coverage   90.24%   90.30%   +0.06%     
==========================================
  Files          29       29              
  Lines        3301     3302       +1     
==========================================
+ Hits         2979     2982       +3     
+ Misses        322      320       -2     

Impacted Files	Coverage Δ
magicgui/widgets/_function_gui.py	97.76% <ø> (+1.11%)	⬆️
magicgui/signature.py	96.62% <100.00%> (+0.03%)	⬆️

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[tlambert03]

added support for tz.curry too... the main difference there was that toolz uses the string __no__default__ as a sentinel, instead of Parameter.empty, to indicate the lack of a value.

In [1]: from functools import partial

In [2]: from toolz import curry

In [4]: def f(x: int, y: str): ...

In [5]: a = partial(f, y='hi')

In [6]: b = curry(f)(y='hi')

In [7]: import inspect

In [8]: inspect.signature(a)
Out[8]: <Signature (x: int, *, y: str = 'hi')>

In [9]: inspect.signature(b)
Out[9]: <Signature (x: int = '__no__default__', *, y: str = 'hi')>

so we need to special case that here. @jni if you wanted to upstream anything, it would be to see whether they can use Parameter.empty as a sentinel instead...

[jni]

@tlambert03 where does parameter.empty come from exactly?

[jni]

(Also this is incredible, I thought my issue might eventually be fixed in a few months... 😂)

[tlambert03]

@tlambert03 where does parameter.empty come from exactly?

In [1]: import inspect

In [2]: inspect.Parameter.empty
Out[2]: <class 'inspect._empty'>

[tlambert03]

and...

In [3]: def f(x): ...

In [4]: inspect.signature(f).parameters
Out[4]: mappingproxy({'x': <Parameter "x">})

In [5]: inspect.signature(f).parameters['x'].default
Out[5]: <class 'inspect._empty'>

[tlambert03]

(Also this is incredible, I thought my issue might eventually be fixed in a few months... 😂)

turned out to be relatively trivial!

[tlambert03]

(Also this is incredible, I thought my issue might eventually be fixed in a few months... 😂)

can I assume this is approved? wanna hit the button? :)