CODEWITHSUNDEEP
pythonparametersdefault-parameters
ires
ires

Reputation: 17

Having trouble with None as default parameter

I am trying to understand how None as the default parameter works. I have a function that has 4 parameters, first is non-default followed by 3 parameters that are set =None.

Function: send(name, website=None, to_email=None, verbose=False)

Calling the function: response = send(name, to_email=email, verbose=True)

My question is when calling the function if I remove the "to_email=" and leave it as just email, an error occurs saying that to_email is None. Doesn't it know that email is passed for to_email parameter (as it's the second parameter I pass)? Why do I have to explicitly say email_to=email when the parameter email_to=None?

This is my code that works:

def send(name, website=None, to_email=None, verbose=False):
    assert to_email != None
    if website != None:
        msg = format_msg(my_name=name, my_website=website)
    else:
        msg = format_msg(my_name=name)
    if verbose:
        print(name, website, to_email)
    # send the message
    send_mail(text=msg, to_emails=[to_email], html=None)

if __name__ == "__main__":
    print(sys.argv)
    name = "Unknown"
    if len(sys.argv) > 1:
        name = sys.argv[1]
    email = None
    if len(sys.argv) > 2:
        email = sys.argv[2]
    response = send(name, to_email=email, verbose=True)
    print(response)

Upvotes: 0

Views: 1458

Answers (1)

Barmar
Barmar

Reputation: 781004

Unnamed arguments are assigned to parameters in the order that they appear in the function definition. So if you write

send(name, email, verbose=True)

the email argument is assigned to the website parameter, since that's the second parameter in the function definition. The to_email parameter gets its default value None.

If you want to skip any parameters, you have to use named arguments for the rest.

If you want to be able to call it the way you're trying, you need to reorder the parameters:

def send(name, to_email=None, website=None, verbose=False):

Now to_email is the second parameter.

Upvotes: 1

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