Base64 Encode & Decode in Python

Encode or decode below — it runs locally in your browser — then grab the canonical Python code. Python's standard-library base64 module works with bytes, so you .encode() a string before encoding and .decode() the result after.

Last updated July 12, 2026

Encode and decode a string

The key pattern is str → .encode() → b64encode() → .decode() → str:

import base64

# Encode
encoded = base64.b64encode("Hello, world!".encode("utf-8")).decode("ascii")
print(encoded)  # SGVsbG8sIHdvcmxkIQ==

# Decode
decoded = base64.b64decode("SGVsbG8sIHdvcmxkIQ==").decode("utf-8")
print(decoded)  # Hello, world!

URL-safe Base64

For JWTs, URLs, and filenames, use the URL-safe alphabet (- and _ instead of + and /):

import base64

# URL-safe encode, padding stripped (JWT-style)
def b64url_encode(data: bytes) -> str:
    return base64.urlsafe_b64encode(data).rstrip(b"=").decode("ascii")

# URL-safe decode, restoring padding
def b64url_decode(s: str) -> bytes:
    s += "=" * (-len(s) % 4)
    return base64.urlsafe_b64decode(s)

Encode a file

import base64

with open("image.png", "rb") as f:
    encoded = base64.b64encode(f.read()).decode("ascii")

# As a data URI for HTML/CSS:
data_uri = "data:image/png;base64," + encoded

For large files or email attachments, base64.encodebytes() inserts a newline every 76 characters (MIME style); pair it with decodebytes(), which tolerates the embedded newlines.

Fixing "Incorrect padding" and invalid input

The most common Python Base64 error is binascii.Error: Incorrect padding — the string's length isn't a multiple of 4, usually because padding = was stripped. Restore it before decoding, and pass validate=True to reject junk instead of silently ignoring it:

import base64, re

def safe_b64decode(s: str) -> bytes:
    s = re.sub(r"\s+", "", s)          # drop stray newlines/spaces
    s += "=" * (-len(s) % 4)           # restore missing padding
    return base64.b64decode(s, validate=True)  # raises on bad chars

Frequently asked questions

How do I Base64 encode a string in Python?

Encode the string to bytes, then Base64-encode: base64.b64encode("Hello".encode("utf-8")).decode("ascii") returns "SGVsbG8=".

How do I Base64 decode in Python?

base64.b64decode("SGVsbG8=") returns b"Hello"; add .decode("utf-8") for a string.

How do I do URL-safe Base64?

Use base64.urlsafe_b64encode() / urlsafe_b64decode(), and .rstrip(b"=") to drop padding.

Why does b64encode raise a TypeError?

It needs bytes, not str. Call .encode("utf-8") on the string first.

How do I fix "Incorrect padding"?

Restore the missing = before decoding: s += "=" * (-len(s) % 4), then base64.b64decode(s). Strip any whitespace first if the string came from a file or network response.