Parameters and Arguments

The function in the previous lesson always printed the same message. A parameter lets a function receive information and use different values on different calls.

def greet(name):
    print(f"Hello, {name}!")

The name inside the definition’s parentheses is a parameter:

def greet(name):
          # ^ parameter

It is a variable that will receive a value when the function is called.

greet("Mina")
      # ^ argument

The value in the call is an argument.

Use the words consistently:

• A parameter is a variable named in a function definition.

• An argument is a value supplied in a function call.

People sometimes use the words loosely, but this distinction makes it much easier to explain what code is doing.

One definition, different arguments

Each call creates a new run of the function body. During the first call, name holds "Mina". During the second, it holds "Jon".

The function does not need a separate version for every person. Its parameter describes the part that may change.

More than one parameter

Separate parameters with commas:

def show_score(player, points):
    print(f"{player} scored {points} points.")

Calls supply one argument for each parameter:

show_score("Maya", 8)
show_score("Omar", 11)

By default, Python matches them by position:

Reversing the arguments still produces valid Python, but the message no longer makes sense:

show_score(8, "Maya")
# 8 scored Maya points.

The function can only work with the meaning you give each position.

Choose parameters that belong to the job

A parameter should be information the function genuinely needs. describe_trip needs a person’s name and a destination, so two parameters make sense.

It does not need every variable in the program. Passing unrelated information makes a function harder to understand and call correctly.

This is your first small design decision: identify what changes from call to call, and make that information a parameter.

def show_price(amount):
    print(f"Price: {amount}")

show_price(12)