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Concepts·Certified Associate Python Programmer

Python bytearray and Binary Files

The last part of PCAP objective 5.5. `bytes` is immutable and `bytearray` is its mutable sibling - a sequence of integers 0 to 255 that you can assign into. Binary mode (`rb`, `wb`) reads and writes those directly, with no decoding, which is the only way to handle a file that is not text. `readinto` fills a buffer you already own and is the one function here that is genuinely unusual.

Files and Streams Guide 25 of 25 Advanced

Written against the versions above. `bytes` and `bytearray` are Python 3 types. In Python 2, `str` was bytes and `bytearray` existed but was rarely used. Everything on this page is Python 3 only.

One machine, and any shell with Python 3 will do - these exams test the language, not a distribution.
Server NameIP AddressOSRolesCPURAMHDD
RUNNER01192.168.0.27Ubuntu 26.04 LTSPython 3.14.4 - the only machine this path needs2 Core4 GB50 GB

Before you start

  1. A bytearray is a mutable bytes

  2. The two ways it refuses

  3. Building one

  4. Writing a binary file

  5. readinto, into a buffer you already own

  6. Why text mode is not an option for binary data

  7. What the exam does with this objective

Official sources

← All PCAP guides