How to Decode Base64 in Python: Simple Guide

To decode base64 in Python, use the base64.b64decode() function from the base64 module. Pass the base64 encoded string as bytes or ASCII string to this function to get the original decoded bytes.

Syntax

The basic syntax to decode a base64 encoded string in Python is:

• base64.b64decode(s): Decodes the base64 encoded bytes or ASCII string s.
• The input s must be bytes or ASCII string.
• The output is bytes representing the original data before encoding.

python

import base64

decoded_bytes = base64.b64decode(s)

Example

This example shows how to decode a base64 encoded string back to the original text.

python

import base64

# Base64 encoded string (represents 'Hello, friend!')
encoded_str = 'SGVsbG8sIGZyaWVuZCE='

# Decode base64 string to bytes
decoded_bytes = base64.b64decode(encoded_str)

# Convert bytes to string using UTF-8
decoded_str = decoded_bytes.decode('utf-8')

print(decoded_str)

Output

Hello, friend!

Common Pitfalls

Common mistakes when decoding base64 in Python include:

• Passing a Unicode string with non-ASCII characters instead of bytes or ASCII string.
• Not decoding the bytes result to a string if you want readable text.
• Ignoring padding characters = which are required for correct decoding.

Example of wrong and right usage:

python

import base64

# Wrong: Passing a Unicode string with non-ASCII characters
try:
    base64.b64decode('äöü')
except Exception as e:
    print(f'Error: {e}')

# Right: Pass ASCII base64 string or bytes
correct = base64.b64decode('SGVsbG8=')
print(correct.decode('utf-8'))

Output

Error: Non-base64 digit found
Hello

Quick Reference

Summary tips for base64 decoding in Python:

• Use base64.b64decode() to decode base64 data.
• Input must be bytes or ASCII string.
• Output is bytes; decode to string if needed.
• Handle exceptions for invalid input.

Key Takeaways

Use base64.b64decode() from the base64 module to decode base64 data.

Input must be bytes or ASCII string; output is bytes.

Decode bytes to string if you want readable text.

Watch out for invalid characters or missing padding in input.

Always handle exceptions for robust decoding.