Python bytearray() Function

The bytearray() function in Python is used to create a mutable sequence of bytes. It’s like a list, but each item is a byte (0 to 255). This is useful when you want to manipulate binary data such as files, images, or streams.

Syntax

bytearray([source[, encoding[, errors]]])

Parameters:

• source (optional) – can be a string, bytes, iterable of integers, or an integer size.
• encoding (optional) – required if the source is a string.
• errors (optional) – how to handle encoding errors ('strict', 'ignore', etc.).

Returns:

• A new bytearray object (mutable bytes).

Example 1: Create an Empty Bytearray

b = bytearray()
print(b)

bytearray(b'')

Example 2: From a List of Integers

b = bytearray([65, 66, 67])
print(b)

bytearray(b'ABC')

Example 3: From a String with Encoding

b = bytearray("hello", "utf-8")
print(b)

bytearray(b'hello')

Example 4: Modify Bytearray

b = bytearray("hello", "utf-8")
b[0] = 72  # Replace 'h' with 'H'
print(b)

bytearray(b'Hello')

Use Cases of bytearray()

• Modify byte-level data (e.g., in file I/O or network sockets)
• Efficiently handle binary data (images, audio, etc.)
• Useful for encryption, hashing, and compression tasks

Common Mistakes

• Forgetting encoding: When creating from a string, always specify encoding.
• Invalid integers: Values in iterable must be between 0 and 255.

Interview Tip

In low-level system or network programming, you may be asked to handle binary protocols. Knowing bytearray() is essential when you need mutable binary structures.

Summary

• bytearray() creates a mutable array of bytes.
• Supports multiple input types: string, list, bytes, or integer.
• Commonly used for working with binary files and buffers.

Practice Problem

Write a program that converts a user-entered string into a bytearray, modifies the first character, and prints the result.

text = input("Enter a word: ")
b = bytearray(text, "utf-8")
b[0] = b[0] - 32  # Make first character uppercase
print("Modified:", b)