This package helps you create decorators that alter the signatures of decorated functions in predictable ways, namely inserting/removing arguments from the front and inserting/removing keyword arguments.

The simplest way to use signature-altering looks like this:

@decorator
def no_op_decorator(f, *args, **kwargs):
    return f(*args, **kwargs)

For the rest of the examples we will assume the decorator will be used as follows:

@spam
def ham(a, b):
    return a + b

Suppose we want ham to behave like this:

>>> ham(100, 2, 3)
95

We would need to provide a definition of spam like this:

@decorator
def spam(f, prefix, *args, **kwargs):
    return prefix - f(*args, **kwargs)

Note that ham now has a different signature from how it was defined.

If we, on the other hand, want to supply fewer arguments, like this:

>>> ham(7)
107

We would do this:

@decorator(insert_args=1)
def spam(f, *args, **kwargs):
    return f(100, *args, **kwargs)

Keyword arguments work mostly the same, except we need to supply the names when inserting them:

@decorator(insert_kwargs='a b')
def spam(f, *args, **kwargs):
    return f(*args, a=7, b=5, **kwargs)

signature-altering is distributed on PyPI as a universal wheel and is available on Linux/macOS and Windows and supports Python 3.5+ and PyPy.

$ pip install signature-altering

signature-altering is distributed under the terms of the MIT License.