Getting all arguments and values passed to a function

Question

I have a Python function, fetch_data, that goes and hits a remote API, grabs some data, and returns it wrapped in a response object. It looks a bit like the below:

def fetch_data(self, foo, bar, baz, **kwargs):     response = Response()     # Do various things, get some data     return response 

Now, it's possible that the response data says "I have more data, call me with an incremented page parameter to get more". Thus, I'd essentially like to store "The Method Call" (function, parameters) in the response object, so I can then have a Response.get_more() which looks at the stored function and parameters, and calls the function again with (almost) the same parameters, returning a new Response

Now if fetch_data were defined as fetch_data(*args, **kwargs) I could just store (fetch_data, args, kwargs) in response. However I have self, foo, bar and baz to worry about - I could just store (fetch_data, foo, bar, baz, kwargs) but that's a highly undesirable amount of repetition.

Essentially, I'm trying to work out how to, from within a function, get a completely populated *args and **kwargs, including the function's named parameters.

Answer 1

Essentially, I'm trying to work out how to, from within a function, get a completely populated *args and **kwargs, including the function's named parameters.

How about saving the arguments via locals() at the beginning of the function?

def my_func(a, *args, **kwargs):     saved_args = locals()     print("saved_args is", saved_args)     local_var = 10     print("saved_args is", saved_args)     print("But locals() is now", locals())  my_func(20, 30, 40, 50, kwarg1='spam', kwarg2='eggs') 

It gives this output:

saved_args is {'a': 20, 'args': (30, 40, 50), 'kwargs': {'kwarg1': u'spam', 'kwarg2': u'eggs'}} saved_args is {'a': 20, 'args': (30, 40, 50), 'kwargs': {'kwarg1': u'spam', 'kwarg2': u'eggs'}} But locals is now {'a': 20, 'saved_args': {...}, 'args': (30, 40, 50), 'local_var': 10, 'kwargs': {'kwarg1': u'spam', 'kwarg2': u'eggs'}} 

Hat tip: https://stackoverflow.com/a/3137022/2829764

Answer 2

Not something I'd do, but you could use inspect.signature to introspect the arguments your method takes:

>>> import inspect >>> def foobar(foo, bar, baz): ...     return inspect.signature(foobar) ...  >>> foobar(1, 2, 3) <Signature (foo, bar, baz)> 

The returned Signature instance has an ordered collection of parameters (the .parameters attribute) which can then be used together with locals() to produce a list of your argument values:

>>> def foobar(foo, bar, baz): ...     sig, foobar_locals = inspect.signature(foobar), locals() ...     return [foobar_locals[param.name] for param in sig.parameters.values()] ... >>> foobar(1, 2, 3) [1, 2, 3] 

However, you really only need such magic when doing advanced function decorators and the like. I think it's overkill here.