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How to define a function in Python

Onyejiaku Theophilus Chidalu

A function is simply a container for a few lines of code that perform a simple task. All programming languages have functions as a common feature. Functions allow developers to write blocks of code that perform specific and reusable tasks. A function can be executed as many times as the developer wants throughout their code.

Functions in Python

In Python, there are two types of functions:

  • Built-in functions
  • User-defined functions

Built-in functions are those functions pre-installed in Python. Examples include:

  • print(): to print an object to the terminal.
  • help(): to ask for help.
  • min(): to get the minimum value.

User-defined functions are those functions defined by the user. Examples include:

  • def greet_customer()
  • def calculate()
  • def take_square()

They all are defined by the user to help them perform certain tasks when writing a program.

How to define a function

Defining a function in Python simply means to create a function. Functions in Python are created and denoted using the keyword def, followed by a function name. For example, greet_user followed by a set of parenthesis().

When a function is defined, every letter of the function must be in lowercase.


Let’s create a simple function that helps us greet a customer. The function will return the following statements:

  • Hello
  • welcome aboard to the home of delicacies


# defining a funtion that will greet a customer
def greet_customer():
  print('welcome aboard to the home of delicacies')

# calling the function


  • In the code above, we used the def keyword to show that we are defining a function.

  • The name of our function is greet_customer(). The parenthesis () are where the parameters of the functions are stored. The double line breaks must be included after defining a function.

  • The greet_custumer() function is used to called the key function. Without calling the key function, the program will not execute the defined function.




Onyejiaku Theophilus Chidalu

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