black-magic 0.0.5

black_magic.decorator.wraps

You can use it just like the standard functools.wraps function:

>>> from black_magic.decorator import wraps

>>> x = []
>>> def real(a:int, b=x) -> "Returns b":
...     return b

>>> @wraps(real)
... def fake(*args, **kwargs):
...     print("Fake!")
...     return real(*args, **kwargs)

This will not only update the docstring of the fake function to look like the original but generate a wrapper function that has exactly the same signature:

>>> assert fake(1) is x   # check object-identity of default-parameter!
Fake!

>>> from inspect import signature
>>> assert signature(fake) == signature(real)

If you want to get real crazy you can even use ast.expr’s:

>>> import ast
>>> fake = wraps(real)(ast.Num(n=1))
>>> fake(0)
1

WARNING: Do NOT use black_magic.decorator.wraps with functools.partial! It won’t work (in most cases).

black_magic.decorator.partial

This is similar to the functools.partial function.

>>> from black_magic.decorator import partial

>>> def real(arg):
...     print(arg)
>>> partial(real, arg=0)()
0

There are some differences, though:

• this function returns a function object which looks like the input function, except for the modified parameters.

• all overwritten parameters are completely removed from the signature. In functools.partial this is true only for arguments bound by position.

• the **kwargs are stripped first, then *args

  >>> partial(lambda a,b,c: (a,b,c), 2, a=1)(3)
  (1, 2, 3)

• by leaving the func argument empty partial can act as decorator:

  >>> @partial(None, bar=0)
  ... def foo(bar):
  ...     print(bar)
  >>> foo()
  0