CODEWITHSUNDEEP
pythonpython-3.xkeyword-argument
user3240688
user3240688

Reputation: 1335

How to iterate over named keyword arguments?

How do you iterate over keyword arguments in a Python function? For example, say I have the following method:

class Car():
    def start_engine(self, key, *, driver=None, passenger=None,  gas=None):
        for k,v in <ITERATE_OVER_KEYWORD_ARGUMENT>:
            if v is not None:
                print(f"KEY: {k}    VALUE:{v}")

c = Car()
c.start_engine(key, driver="Bob", passenger="Alice")

Should print:

driver: Bob   
passenger: Alice

I didn't want to use **kwargs because I wanted to name my arguments. I can't just call locals() because I have other arguments.

I guess I could make a helper function that takes in **kwargs and then build a dict, and then I'd call that function with all my keyword arguments, but that seems hacky.


def to_dict(**kwargs):
    d = {k:v for k,v in kwargs.items() if v is not None}
    return d

That works, but seems like such a strange way to accomplish what I'm trying to do.

Is there an acceptable way to to iterate through keyword arguments, or is that bad Python for some reason?

Upvotes: 5

Views: 1610

Answers (1)

wim
wim

Reputation: 363213

In your case they are all optional keyword-only arguments (i.e. arguments with default values) so you can use:

for k in self.start_engine.__kwdefaults__:
    v = locals()[k]

This simple approach will fail to capture keyword-only arguments without default values. The Car shown in your question does not use any, but in case one needs to support those "required keyword" arguments, you may need to inspect signature:

>>> import inspect
>>> class Car:
...     def start_engine(self, key, *, driver=None, passenger=None, dog, gas=None):
...         sig = inspect.signature(self.start_engine)
...         for k, v in sig.parameters.items():
...             if v.kind is inspect.Parameter.KEYWORD_ONLY:
...                 print(k, locals()[k])
...
>>> Car().start_engine("key", gas="unleaded", dog="ridgeback")
driver None
passenger None
dog ridgeback
gas unleaded

Upvotes: 4

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