Python Function Parameters

In Python, a function is a block of code that is given a name and can be called repeatedly. Functions can take in input values, called parameters, and return output values.

When you define a function, you can specify the parameters that the function takes in. The parameters are listed in the function definition, after the function name and before the colon (:). For example, the following function definition defines a function called add that takes in two parameters, x and y:

Code snippet

def add(x, y):
    return x + y

When you call a function, you pass in the values for the parameters. The values are separated by commas and are placed inside the parentheses after the function name. For example, the following code calls the add function and passes in the values 1 and 2:

Code snippet

result = add(1, 2)

The value returned by the function is stored in the variable result. You can then use the value of result in other parts of your code.

Parameters are declared in the function definition, and they are separated by commas. The name of the parameter is followed by a colon (:) and the type of the parameter. For example, the following function definition declares two parameters:

Python

def my_function(parameter1: int, parameter2: str) -> None:
  pass

Parameters can be of any type, including numbers, strings, lists, and dictionaries. You can also specify default values for parameters. If you do not pass in a value for a parameter with a default value, the default value will be used. For example, the following function definition defines a function called greet that takes in a name parameter and has a default value of "World":

Code snippet

def greet(name="World"):
    print("Hello, " + name + "!")

When you call the greet function without passing in a value for the name parameter, the default value of "World" will be used. For example, the following code calls the greet function:

Code snippet

greet()

This will print the following output:

Code snippet

Hello, World!

You can also pass in keyword arguments to functions. Keyword arguments are named arguments that are passed in after the positional arguments. For example, the following code calls the greet function and passes in the keyword argument name="John":

Code snippet

greet(name="John")

This will print the following output:

Code snippet

Hello, John!

Here is an example of a function definition with two parameters:

Python

def my_function(parameter1, parameter2):
    """This function takes two parameters and prints them."""
    print(parameter1)
    print(parameter2)

When this function is called, the caller can pass in any value for the parameters. For example, the following code calls the my_function() function and passes in the values "Hello" and 10:

Python

my_function("Hello", 10)

When the function is called, the values that are passed in are assigned to the parameters. In this case, the value "Hello" is assigned to the parameter parameter1, and the value 10 is assigned to the parameter parameter2. The function then prints the values of the parameters.

Parameters can be of any type, including strings, numbers, lists, dictionaries, and objects. They can also be optional, which means that the caller does not have to pass in a value for them. For example, the following function definition has an optional parameter:

Python

def my_function(parameter1, parameter2=None):
    """This function takes two parameters, one of which is optional."""
    if parameter2 is None:
        print("parameter2 is not set")
    else:
        print(parameter2)

When this function is called without passing in a value for parameter2, the value of parameter2 will be None. When the function is called with a value for parameter2, that value will be assigned to the parameter.

Parameters can also be used to pass in objects. For example, the following function definition takes in a list of numbers and returns the sum of the numbers:

Python

def sum_numbers(numbers):
    """This function takes in a list of numbers and returns the sum of the numbers."""
    sum = 0
    for number in numbers:
        sum += number
    return sum

When this function is called, the caller can pass in any list of numbers. For example, the following code calls the sum_numbers() function and passes in the list [1, 2, 3, 4, 5]:

Python

sum = sum_numbers([1, 2, 3, 4, 5])
print(sum)

When the function is called, the list of numbers that is passed in is assigned to the parameter numbers. The function then iterates over the list and adds each number to the variable sum. The function then returns the value of sum.

Parameters are a powerful tool that can be used to pass in data into functions. Parameters are a powerful way to make your code more reusable and modular. They can be used to pass in any type of data, including strings, numbers, lists, dictionaries, and objects. Parameters can also be used to pass in objects. By using parameters, you can define functions that can be used with different sets of input values. This can make your code more efficient and easier to understand.