Can I call function in python with named arguments as a variable?

Question

For example

username_type = 'email'

def get_user_by(email=None, username=None):
    if email:
        return user.get_by_email(email)
    elif username:
        return user.get_by_username(username)

get_user_by(username_type = username)

Of course this line won’t work
get_user_by(username_type = username)
But I want something like this to make it work

I don’t know which type will I get the user from but I want the named argument based on variable

Asked By: Fathey Abdel slam

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Source

Answer 1

You can pass a dictionary of keywords arguments to a function using the ** operator. The keys of the dictionary are the parameter names in the function.

In this case, that could be:

get_user_by(**{username_type: username})

If the variable username_type has the value 'email' then the username would be received in get_user_by as the keyword argument email.

Answered By: khelwood

Answer 2

I think the OP could use a little more detail. The * and ** notation are used to pack and unpack in python, * to pack and unpack a list and ** to pack and unpack a dictionary. For example,

[1,2,3,*[4,5,6]]               #The inside list will be unpacked into the overall list. 
{'a':1,'b':2, **dict(z=7,w=8)} #The dictionary will be unpacked into the outside dictionary.

This also works with function calls and definitions.

def f(*args): #pack all args into a list called args. 
    return args
print(f(1,2,3))
y = [1,2,3]
f(*y)        #Unpack y into f, same as f(1,2,3)

def f(**kargs): #pack all keyword-args into a dictionary called kargs. 
    return kargs.get('thing',None)
print(f(x=7))
print(f(thing=7))

Answered By: Bobby Ocean

Answer 3

If one needs a more generalized solution, both for positional and named arguments, one should replace the line

get_user_by(username_type = username)

with a decorator-like code:

def args_passer(args, kwargs):
    def out():
        return get_user_by(*args, **kwargs)
    return out()
args_passer([], {username_type: username})

Answered By: Kostiantyn Ivashchenko

Can I call function in python with named arguments as a variable?

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