all Python 3binasciifunction

binascii.a2b_base64()

base64

Decodes base64 to bytes. By default it silently skips stray characters; strict_mode=True (3.11+) demands strict RFC 4648.

Syntax

binascii.a2b_base64(string, /, *, strict_mode=False)

Lenient mode forgives spaces, newlines and junk, which helps with email but is risky for input validation: 'aG k=' decodes without complaint. Missing '=' at the end raises binascii.Error 'Incorrect padding', a common issue with base64 from URLs where '=' was trimmed; append '=' * (-len(s) % 4) to fix it. It also accepts ASCII str.

Examples

import binascii
print(binascii.a2b_base64('aG k=\n'))  # → b'hi'
s = 'aGk'
print(binascii.a2b_base64(s + '=' * (-len(s) % 4)))  # → b'hi'
try:
    binascii.a2b_base64(s)
except binascii.Error as e:
    print(e)  # → Incorrect padding

# Python 3.11+
import binascii
try:
    binascii.a2b_base64('aG k=', strict_mode=True)
except binascii.Error as e:
    print(e)  # → Only base64 data is allowed

See also

Common errors

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