If you aim to optimize your code for reusability, Python functions are indispensable.

Functions allow you to execute specific blocks of code multiple times without redundancy.

In programming, giving each function a unique name is crucial for its identification. When you invoke this name, it prompts the execution of a predefined code block associated with it.

**Related Course: ** Complete Python Programming Course & Exercises

Understanding Python Functions

Functions are fundamental building blocks in coding. They partition your code into specific segments or modules. This structured approach enhances code clarity and simplifies debugging. An everyday function in Python you might have encountered is the print function:

print("Hello world")

The beauty of functions is their reusability. You can call the same function multiple times:


Creating a Python Function

To define a function in Python, adhere to the following syntax:

def <function_name>([<parameters>]):

Here’s a breakdown:

  • def signals Python that you’re defining a function.
  • function_name is the name of your function and should be unique in your code.
  • parameters are optional inputs that your function can utilize.
  • : concludes the function header.
  • <statement(s)> are the actions or commands within the function, also known as the function’s body. Always remember to indent them by four spaces.

Let’s see a simple function f() in action:

def f():
print('function body')

# Calling the function

Given that functions are reusable, invoking it multiple times is straightforward:


Your function’s body can also span several lines:

def hello():
print("Dear Java")
print("How's the JRE development going?")
print("Yours sincerely,")

python function

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Function Parameters and Arguments

Parameters are the input values that functions can accept. Always ensure they maintain their order when used:

def hello(name):
print("Good day, " + name)


To define multiple parameters, separate them with commas:

def f(name, salary):
print(f"{name} earns ${salary} annually")

f("Alice", 80000)

When calling a function, always ensure that the arguments match the order and number set in the function’s definition. The pass keyword in Python denotes a function with no operations.

Utilizing Default Parameters

Default parameters provide values to a function when no arguments are supplied. These values act as fallbacks:

def f(x=5,y=4):
print(f"{x} and {y}")

f() # Outputs: 5 and 4
f(3) # Outputs: 3 and 4
f(10,10) # Outputs: 10 and 10

Understanding Function Scope

Variables declared within a function remain constrained to that function. They’re inaccessible outside its boundaries. To make a function’s internal variable available outside, employ the return keyword.

The Power of the Return Statement

Using return, functions can produce outputs which can then be stored in variables for further use:

def sum(a,b):
result = a + b
return result

total = sum(100,60)
print(total) # Outputs: 160
python function return variable

Functions in Python are flexible enough to return multiple values simultaneously:

def f(a,b,c):
return a, b, c

x, y, z = f(1,2,3)

Handling Variable-Length Arguments

Sometimes, the number of arguments a function should accept can be variable. To accommodate this, use lists or tuples:

def f(*args):
for item in args:

Embracing Docstrings

Docstrings offer a documentation mechanism for functions, helping users understand their purpose and usage. Always strive to document complex or non-intuitive parts of your code.

The Significance of the main() Function

The main() function, commonly used in Python scripts, serves as the program’s entry point. It’s especially useful for scripts meant to be both standalone and importable modules.

Summing Up

Functions are an integral part of Python programming, offering structure and reusability. In this guide, you discovered the ins and outs of Python functions, from their creation and invocation to advanced features like default parameters and docstrings.

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