[Feature Request] @beartype + functools.partial support

[leycec]

This feature request comes courtesy @danielward27 at issue #368, who astutely noted that the @beartype decorator currently fails to support functools.partial objects. Notably, this questionable minimal example coercing the functools.partial class into a decorator:

from beartype import beartype
from functools import partial

@beartype
@partial(partial, b=2)  # <-- WTH!?!? no way that actually works. no way...
def fn(a, b=2):
    return a + b

fn(1)  # <-- OMG!!!! @partial(partial, b=2) totally works. Mind. Is. Blown.

...currently raises this mostly unreadable exception:

AssertionError: <method-wrapper '__call__' of functools.partial object at
0x7f70b1957a60> not builtin bound method descriptor.

Just thinking about supporting this makes @leycec vomit all over himself. 🤮

[danielward27]

FWIW I promise I don't actually write code like the above example.

A pattern that is used a lot in jax is something like

@beartype
@partial(jax.jit, static_argnames=["length"])
def fn(a, length=2):
    return a + jnp.ones(length)
fn(1)

i.e. to partially apply arguments to a decorator before wrapping. My double partial was a lazy proxy for that (since jit leads to an error anyway), but perhaps I chose a bad proxy, since this seems to work

from beartype import beartype
from functools import partial

def add_decorator(fn, add):
    return lambda *args, **kwargs: fn(*args, **kwargs) + add

@beartype
@partial(add_decorator, add=5)
def fn(a):
    return a