Bytes and Bytearray

Python · Reference cheat sheet

📋 Overview

bytes is an immutable sequence of ints 0–255; bytearray is mutable. Use for binary protocols, files, and encodings. Text is str — convert explicitly with .encode() / .decode().

🔧 Core concepts

Encoding: s.encode("utf-8") → bytes; b.decode("utf-8") → str. Hex/base helpers: .hex(), bytes.fromhex.

💡 Examples

Encode / decode:

text = "café"
data = text.encode("utf-8")
print(data)                 # b'caf\xc3\xa9'
print(data.decode("utf-8"))

bytearray mutation:

buf = bytearray(b"python")
buf[0] = ord("P")
buf.extend(b"!")
print(buf)                  # bytearray(b'Python!')

Binary file + memoryview:

from pathlib import Path

path = Path("blob.bin")
path.write_bytes(b"\x00\x01\x02\x03")
raw = path.read_bytes()
view = memoryview(raw)
print(view[1:3].tobytes())  # b'\x01\x02'

Struct packing:

import struct

packet = struct.pack(">I4s", 42, b"ping")
code, payload = struct.unpack(">I4s", packet)
print(code, payload)

⚠️ Pitfalls

• Indexing returns int, not a 1-length bytes: b"ab"[0] == 97.
• Mixing str and bytes raises TypeError.
• Wrong encoding (e.g. latin-1 vs utf-8) corrupts text — be explicit.
• bytes(5) is five zero bytes, not b"5".
• Large concatenations in a loop — prefer bytearray or b"".join.

🔗 Related

• Strings
• Files I/O
• Slicing
• Types
• Examples: encrypt
• Pathlib