Python Printing None: Complete Fix Guide

When you call a function that doesn’t explicitly return a value, Python automatically returns None. In your code, function_2() prints the text but doesn’t return anything, so when you wrap it in print(), you’re printing that None result.

Contents

• Understanding the Problem
• Solution 1: Remove the Print Statement
• Solution 2: Modify Function to Return Values
• Common Mistakes to Avoid
• Best Practices for Function Design
• Complete Fixed Code
• Testing Your Solution

Understanding the Problem

The issue occurs because function_2() performs an action (printing) but doesn’t return any value. In Python, when a function reaches the end without a return statement, it automatically returns None.

Let’s trace what happens step by step:

# Current code behavior:
for i in foods_list:
    print(function_2(i))  # This does two things:
                          # 1. Calls function_2(i) which prints the food statement
                          # 2. Prints the return value of function_2(i), which is None

Solution 1: Remove the Print Statement

The simplest fix is to remove the print() wrapper around function_2(i) since the function already handles the printing:

def function_3():
    foods_list = function_1()
    for i in foods_list:
        function_2(i)  # Just call the function, don't print its result

Why this works: Now you’re only calling function_2(i) which prints the food statement, but you’re not trying to print the return value (which would be None).

Solution 2: Modify Function to Return Values

An alternative approach is to change function_2() to return the string instead of printing it, then print the returned value in function_3():

def function_2(temp):
    return "{0} is one of my favorite foods".format(temp)

def function_3():
    foods_list = function_1()
    for i in foods_list:
        print(function_2(i))  # Now this makes sense

Why this works: Now function_2() returns a string, and print() prints that string instead of None.

Common Mistakes to Avoid

1. Mixing print and return: Don’t make a function both print and return values unless you have a specific reason to do so. Choose one approach.

2. Forgetting return statements: Remember that Python functions return None by default if no return statement is reached.

3. Printing function calls unnecessarily: If a function already prints what you need, don’t wrap it in another print().

Best Practices for Function Design

Here’s a comparison of different approaches:

Recommendation: For most cases, design functions to return values rather than print directly. This makes your code more reusable and testable.

Complete Fixed Code

Here’s the corrected version using Solution 1:

def function_1():
    foods = ["Apple", "Orange", "Banana"]
    return foods

def function_2(temp):
    print("{0} is one of my favorite foods".format(temp))

def function_3():
    foods_list = function_1()
    for i in foods_list:
        function_2(i)  # Fixed: removed print() wrapper

function_3()

Output:

Apple is one of my favorite foods
Orange is one of my favorite foods
Banana is one of my favorite foods

Testing Your Solution

To verify your fix works, here are some test cases you can try:

# Test with different food lists
def function_1_different():
    return ["Pizza", "Sushi", "Tacos"]

def test_different_foods():
    foods_list = function_1_different()
    for food in foods_list:
        function_2(food)

# Test with empty list
def test_empty_list():
    foods = []
    for food in foods:
        function_2(food)  # Should print nothing

# Run tests
print("Testing different foods:")
test_different_foods()

print("\nTesting empty list:")
test_empty_list()

This should help you understand the pattern and apply it to other similar situations in your code.

Sources

1. Stack Overflow - Why is this printing ‘None’ in the output?
2. Real Python - Understanding Python’s return statement
3. Python Documentation - Defining Functions