Decorator for aliasing kwargs in Python functions

deprecated_kwarg.py

#!/usr/bin/env python
import warnings
from functools import wraps


def deprecated_kwarg(old, new, version):
    def decorator(func):
        @wraps(func)
        def func_wrapper(*args, **kwargs):
            new_kwargs = kwargs.copy()
            if old in kwargs:
                warnings.warn(
                    "kwarg '{}' will be removed in version {}"
                    ", switch to '{}' instead.".format(old, version, new),
                    category=DeprecationWarning)

                del new_kwargs[old]

                if new in kwargs:
                    warnings.warn(
                        "Deprecated kwarg '{}' ignored, using '{}'".format(old, new),
                        category=DeprecationWarning)
                else:
                    new_kwargs[new] = kwargs[old]

            return func(*args, **new_kwargs)
        return func_wrapper
    return decorator


# Tests
if __name__ == "__main__":
    def add(one, two):
        return one + two

    @deprecated_kwarg(old='one', new='first', version='1.0.0')
    @deprecated_kwarg(old='two', new='second', version='1.0.0')
    def add2(first, second):
        return first + second

    warnings.simplefilter('always', DeprecationWarning)

    assert \
        add(1, 2) == \
        add2(1, 2) == \
        add(one=1, two=2) == \
        add2(first=1, second=2) == \
        add2(one=1, two=2) == \
        add2(one=1, first=1, two=2, second=2)

    warnings.simplefilter('default', DeprecationWarning)

⭆ python deprecated_kwargs.py
/tmp/try.py:15: DeprecationWarning: kwarg 'one' will be removed in version 1.0.0, switch to 'first' instead.
  category=DeprecationWarning)
/tmp/try.py:15: DeprecationWarning: kwarg 'two' will be removed in version 1.0.0, switch to 'second' instead.
  category=DeprecationWarning)
/tmp/try.py:15: DeprecationWarning: kwarg 'one' will be removed in version 1.0.0, switch to 'first' instead.
  category=DeprecationWarning)
/tmp/try.py:22: DeprecationWarning: Deprecated kwarg 'one' ignored, using 'first'
  category=DeprecationWarning)
/tmp/try.py:15: DeprecationWarning: kwarg 'two' will be removed in version 1.0.0, switch to 'second' instead.
  category=DeprecationWarning)
/tmp/try.py:22: DeprecationWarning: Deprecated kwarg 'two' ignored, using 'second'
  category=DeprecationWarning)