What is a Positional Argument?

  • When you call a function, Python must match the argument in the function call with a parameter in the function definition. The simplest way to do this is based on the order of the arguments provided. Values matched this way are called positional arguments.

  • Example: Consider a function that displays information about website users. The following function tells us the userā€™s email address and the userā€™s last name.

python
1def user(emailAddress, lastName):
2    print("\nUser's Email Address: " + emailAddress)
3    print("User's Last Name: " + lastName.title())
4
5user("hbulldog@student.wcu.edu", "bulldog")

Output:

1User's Email Address: hbulldog@student.wcu.edu
2User's Last Name: Bulldog
  • The function above shows that this function needs a userā€™s email address and last name.
  • When user() is called, we need to provide an email address and last name, in that order.
  • In the function call, the argument ā€œhbulldog@student.wcu.eduā€ is stored in the parameter emailAddress and the argument bulldog is stored in the lastName parameter.

What is a Keyword Argument?

  • A keyword argument is a name-value pair that you pass to a function. You directly associate the name and the value within the argument.
  • Example: Letā€™s rewrite the above example code using keyword arguments to call user.
python
1def user(emailAddress, lastName):
2    print("\nUser's Email Address: " + emailAddress)
3    print("User's Last Name: " + lastName.title())
4
5user(emailAddress="hbulldog@student.wcu.edu", lastName="bulldog")
  • Note that the function user hasnā€™t changed. However, when we call the function, we explicitly tell Python which parameter each argument should be matched with.

Variable (Arbitrary) Keyword Arguments:

  • A variable/arbitrary number of arguments allow you to place a special argument, usually called kwargs, with two asterisks before it.
  • This will all you to write functions that accept as many key-value pairs as the calling statement provides. The function would look something like this:
python
1def user(emailAddress, **kwargs):
2    print("\nUser's Email Address: " + emailAddress)
3    print("User's First Name: " + kwargs["firstname"].title())
4
5user(emailAddress="hbulldog@student.wcu.edu", 
6     lastName="bulldog", 
7     firstname="harpua")
  • Note that we donā€™t have to use the double asterisks when weā€™re referring to kwargs inside the function.
  • The definition of user() expects an email address, and then it allows the user to pass in as many name-value pairs as they want.

Output:

1User's Email Address: hbulldog@student.wcu.edu
2User's First Name: Harpua