5 Best Ways to Write a List of Bytes to a Binary File in Python

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💡 Problem Formulation: Python developers often need to write byte data directly to a binary file. This task is common when handling binary formats or low-level file interaction. For instance, you might have a list of bytes, like [0x15, 0x1C, 0xFE], and want to write it as binary data to a file named “output.bin”. The goal is to perform this action using techniques that are efficient and Pythonic, suitable for various scenarios.

Method 1: Using the Built-in open() Function with write()

This method involves opening a file in binary write mode using Python’s built-in open() function and then writing a bytes-like object to the file using the file object’s write() method. It’s a straightforward and the most commonly used approach when dealing with binary file operations in Python.

Here’s an example:

byte_list = [0x15, 0x1C, 0xFE]
with open('output.bin', 'wb') as file:
    file.write(bytes(byte_list))

Output: A file named “output.bin” is created with the binary data corresponding to the byte values in the list.

The code opens “output.bin” in binary writing mode (‘wb’). It then converts the list of integers to a bytes object and writes this to the file. When the block completes, the file is automatically closed.

Method 2: Using the array Module

The array module provides an array type that is more efficient than a list for storing numeric data. This method is particularly useful when working with large lists of bytes, as it can be more memory-efficient and performant than a regular list.

Here’s an example:

import array

byte_list = array.array('B', [0x15, 0x1C, 0xFE])
with open('output.bin', 'wb') as file:
    file.write(byte_list)

Output: A binary file that contains the sequence of bytes.

Here we’re using the array module to create an array of bytes (‘B’ type code). The array is then directly written to the file, which is more efficient for larger data sets.

Method 3: Using bytearray

A bytearray in Python is a mutable sequence of bytes. Writing a bytearray to a binary file can be done similarly to writing a bytes object. However, this method gives you the ability to modify the bytes before writing to the file.

Here’s an example:

byte_list = bytearray([0x15, 0x1C, 0xFE])
with open('output.bin', 'wb') as file:
    file.write(byte_list)

Output: The file “output.bin” contains the same sequence of bytes as before.

The byte_list is created as a bytearray, which allows for in-place modifications if needed. The byte_list is then written to the binary file in the same manner as a bytes object.

Method 4: Writing Bytes within a Loop

In cases where you have a complex logic to determine the bytes to write, or if they’re generated on-the-fly, you might write the bytes individually or in small batches within a loop.

Here’s an example:

byte_list = [0x15, 0x1C, 0xFE]
with open('output.bin', 'wb') as file:
    for byte in byte_list:
        file.write(bytes([byte]))

Output: The binary file will have the same output but written in individual byte operations.

This method shows how you can iterate over the byte list and write each byte individually. This technique provides more control but is less efficient for writing large quantities of data due to the overhead of multiple write operations.

Bonus One-Liner Method 5: Using writelines() and List Comprehension

This one-liner approach uses list comprehension to convert the integers to bytes, combined with the writelines() method to write these to a file, making it a concise way to perform the task without explicit loops.

Here’s an example:

byte_list = [0x15, 0x1C, 0xFE]
with open('output.bin', 'wb') as file:
    file.writelines(bytes([byte]) for byte in byte_list)

Output: As with the above methods, a binary file with the corresponding sequence of bytes is created.

This concise method efficiently writes each byte to the file without the need for an explicit loop or creating a large intermediate bytes object.

Summary/Discussion

  • Method 1: Built-in open() Function with write(). Simple and direct. May not be the most efficient for very large data sets.
  • Method 2: Using the array Module. More efficient for large arrays of bytes. Slightly more complex due to module import and typecasting.
  • Method 3: Using bytearray. Allows mutation before writing. Essentially as straightforward as Method 1 with added flexibility.
  • Method 4: Writing Bytes within a Loop. Offers maximum control. Can be inefficient for larger files.
  • Method 5: One-Liner using writelines(). Extremely concise. Good for short lists but lacks clarity for complex operations or very large data sets.