Python convert args to kwargs

Question

I am writing a decorator that needs to call other functions prior to call of the function that it is decorating. The decorated function may have positional arguments, but the f

Answer 1

If you're using Python >= 2.7 inspect.getcallargs() does this for you out of the box. You'd just pass it the decorated function as the first argument, and then the rest of the arguments exactly as you plan to call it. Example:

>>> def f(p1, p2, k1=None, k2=None, **kwargs):
...     pass
>>> from inspect import getcallargs

I'm planning to do f('p1', 'p2', 'p3', k2='k2', extra='kx1') (note that k1 is being passed positionally as p3), so...

>>> call_args = getcallargs(f, 'p1', 'p2', 'p3', k2='k2', extra='kx1')
>>> call_args
{'p2': 'p2', 'k2': 'k2', 'k1': 'p3', 'p1': 'p1', 'kwargs': {'extra': 'kx1'}}

If you know the decorated function won't use **kwargs, then that key won't appear in the dict, and you're done (and I'm assuming there's no *args, since that would break the requirement that everything have a name). If you do have **kwargs, as I have in this example, and want to include them with the rest of the named arguments, it takes one more line:

>>> call_args.update(call_args.pop('kwargs'))
>>> call_args
{'p2': 'p2', 'k2': 'k2', 'k1': 'p3', 'p1': 'p1', 'extra': 'kx1'}

Update: for Python >= 3.3, see inspect.Signature.bind() and the related inspect.signature function for functionality similar to (but more robust than) inspect.getcallargs().