CODEWITHSUNDEEP
pythonkeyword-argument
deadstump
deadstump

Reputation: 965

Passing more kwargs into a function than initially set

Is there a way to send more kwargs into a function than is called for in the function call?

Example:

def mydef(a, b):
    print a
    print b

mydict = {'a' : 'foo', 'b' : 'bar'}
mydef(**mydict)    # This works and prints 'foo' and 'bar'

mybigdict = {'a' : 'foo', 'b' : 'bar', 'c' : 'nooooo!'}
mydef(**mybigdict)   # This blows up with a unexpected argument error

Is there any way to pass in mybigdict without the error? 'c' would never be used in mydef in my ideal world and would just be ignored.

Thanks, my digging has not come up with what I am looking for.

Edit: Fixed the code a bit. The mydef(a, b, **kwargs) was the form that I was looking for, but the inspect function args was a new thing to me and definitely something for my toolbox. Thanks everyone!

Upvotes: 12

Views: 6179

Answers (2)

Martijn Pieters
Martijn Pieters

Reputation: 1121366

No, unless the function definition allows for more parameters (using the **kwargs catch-all syntax), you cannot call a method with more arguments than it has defined.

You can introspect the function and remove any arguments it won't accept however:

import inspect

mybigdict = {'a2' : 'foo', 'b2' : 'bar', 'c2' : 'nooooo!'}
sig = inspect.signature(mydef)
if not any(p.kind == p.VAR_KEYWORD for p in sig.parameters.values()):
    for missing in mybigdict.keys() - sig.parameters.keys():
        del mybigdict[missing]
mydef(**mybigdict)

I'm using the inspect.signature() function to check if the callable supports a **kwarg catch-all (by looking for a Parameter.VAR_KEYWORD entry), and if it doesn't, I use the set difference between mybigdict and the signature .parameters mapping to remove anything the method won't support.

Upvotes: 21

Exelian
Exelian

Reputation: 5888

To clarify Martijn Pieters's answer (for sake of clarity). It's possible if you change the function signature to:

def mydef(a, b, **kwargs):

This means it's not possible without changing the signature. But if that's not a problem it'll work.

Upvotes: 10

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