Defining a Function That Takes More Than One Argument

Defining a function that takes more than one argument is also easy. We just need to put a parameter variable for each argument value in the function definition's parameter list; we separate the parameter names with commas.

Here is a simple example of a function named indent_text that takes two arguments, a string, and an integer. When called, the function will display the given text indented the specified number of spaces.

def indent_text(text, margin):
    left_space = ' ' * margin
    print(left_space + text)

Common Misconceptions

There are a number of misconceptions that can occur when one is just learning about arguments and parameters. The two most common misconceptions deal with:

1. The order of arguments and parameters

2. The names of arguments and parameters

With regard to the order of arguments and parameters, parameter variables are assigned values in the order that the arguments are listed. In other words, the first argument value is assigned to the first parameter variable, the second argument value is assigned to the second parameter variable, and so on. Consider the following example.

01   def print_name_and_age(name, age):
02       print(name, 'is', age, 'years old.')
03 
04   print_name_and_age('Bob', 33)
05   print_name_and_age(33, 'Bob')

Lines 01-02 define a function named print_name_and_age that takes two arguments. Lines 04 and 05 call that function and each call passes two arguments. In the function call on line 04, the argument values passed to the function are 'Bob', and 33, in that order. The same two values are passed as arguments in the function call on line 05; however, the values are passed in the reverse order - the value 33 being passed as the first argument and the value 'Bob' being passed as the second argument.

When you run this code, you will get the following output.

Bob is 33 years old.
33 is Bob years old.

If this seems surprising, it is because of the common misconception that the computer somehow knows what you are trying to say - it does not. The computer simply does exactly what you say, regardless of what you may have meant. For example, when line 04 above executes, the first argument value 'Bob' is assigned to the first parameter variable name, and the second argument value 33 is assigned to the second parameter variable age. And, so the function prints 'Bob is 33 years old.'. When line 05 above executes, the first argument value 33 is assigned to the first parameter variable name, and the second argument value 'Bob' is assigned to the second parameter variable age. And, so the function prints '33 is Bob years old.'.

4.44 Functions.png

With regard to the names of arguments and parameters, the names of variables used as arguments have no impact on which values are assigned to which parameters--the prior rule (parameter variables are assigned values in the order that the arguments are listed) always holds. Consider the following example:

01  def print_name_and_age(name, age):
02      print(name, 'is', age, 'years old.')
03 
04  name = 'Bob'
05  age = 33
06
07  print_name_and_age(name, age)
08  print_name_and_age(age, name)

When you run this code, you will get the following output.

Bob is 33 years old.
33 is Bob years old.

This is again because the computer simply does exactly what you say, regardless of what you may have meant. For example, when line 07 above executes, the first argument variable name evaluates to the value 'Bob', and so the value 'Bob' is assigned to the function's first parameter variable name, and the second argument variable age evaluates to the value 33, and so the value 33 is assigned to the function's second parameter variable age. And, so the function prints 'Bob is 33 years old.'. When line 08 above executes, the first argument variable age evaluates to the value 33, and so 33 is assigned to the function's first parameter variable name, and the second argument variable evaluates to the value 'Bob', and so the value 'Bob' is assigned to the function's second parameter variable age. And, so the function prints '33 is Bob years old.'.

It is important and helpful to realize that, in the eight line example above there are two separate variables named name, and two separate variables named age. A function's parameter variables belong to that function only. They are separate and distinct from any other variable in the program, even if those other variables have the same name as one of the function's parameter variables.