This small library uses Advanced Python Hackery to change the signature of a function to be a mixture of itself and a function that it wraps. It’s like functools.wraps, but it allows the wrapped function to add its own arguments into the mix.

from merge_args import merge_args

def old(foo, bar):
    """This is old's docstring."""
    print(foo, bar)
    return foo + bar

@merge_args(old)
def new(prefix, foo, *args, **kwargs):
    return old(prefix + foo, *args, **kwargs)

or

from merge_args import merge_args

def old(foo, bar):
    """This is old's docstring."""
    print(foo, bar)
    return foo + bar

@merge_args(old, drop_args=["bar"])
def new(prefix, foo, *args, **kwargs):
    return old(prefix + foo, *args, **kwargs)

If you then run help(new), this is the output:

Help on function new in module __main__:

new(prefix, foo, bar)
    This is old's docstring.

I wrote a detailed blog post, describing the ins and outs of how this package works:

https://chriswarrick.com/blog/2018/09/20/python-hackery-merging-signatures-of-two-python-functions/

This module was inspired by F4D3C0D3 on #python (formerly on freenode IRC).

Copyright © 2018-2023, Chris Warrick. All rights reserved.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

1. Redistributions of source code must retain the above copyright notice, this list of conditions, and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions, and the following disclaimer in the documentation and/or other materials provided with the distribution.
3. Neither the name of the author of this software nor the names of contributors to this software may be used to endorse or promote products derived from this software without specific prior written consent.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.