5 Best Ways to Convert a Python List of Bytes to Integer

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💡 Problem Formulation: In Python, you might encounter a scenario where you have a list of bytes, for instance, [0x15, 0x02, 0x50], and your aim is to convert this list into an integer value. For example, treating the list as a big-endian representation of an integer, the expected output is 1388624. This article explores the different methods to perform this conversion, detailing their usage with examples.

Method 1: Using int.from_bytes() with Big-Endian

This method involves the built-in int.from_bytes() function. It interprets a list of bytes as an integer, with big-endian byte order being the most common. Big-endian means the first byte is the most significant byte.

Here’s an example:

byte_list = [0x15, 0x02, 0x50]
int_value = int.from_bytes(byte_list, 'big')
print(int_value)

Output: 1388624

The code creates an integer using a list of bytes, assuming they are organized in big-endian order. The value 1388624 is printed, which is the integer the list represents.

Method 2: Using int.from_bytes() with Little-Endian

Similarly, int.from_bytes() can be used with little-endian byte order, where the last byte in the list is the most significant byte.

Here’s an example:

byte_list = [0x50, 0x02, 0x15]
int_value = int.from_bytes(byte_list, 'little')
print(int_value)

Output: 1399600

This example demonstrates converting a list of bytes to an integer using the little-endian order. The code snippet generates the integer 1399600 from the provided byte list.

Method 3: Using Bitwise Operations

Bitwise operations can also be utilized to convert a list of bytes to an integer. This approach manually shifts the bytes and combines them into an integer.

Here’s an example:

byte_list = [0x15, 0x02, 0x50]
int_value = 0
for byte in byte_list:
    int_value = (int_value << 8) | byte
print(int_value)

Output: 1388624

This code loops through each byte, shifting the current integer value 8 bits to left (which is equivalent to multiplying by 256 for each byte) and then applying the bitwise OR operation, accumulating into the final integer value.

Method 4: Using a For-Loop and Multiplication

Another method to convert a list of bytes to an integer is by multiplying each byte by its corresponding power of 256 (since a byte is 8 bits) and summing the result.

Here’s an example:

byte_list = [0x15, 0x02, 0x50]
int_value = 0
for i, byte in enumerate(reversed(byte_list)):
    int_value += byte << (i * 8)
print(int_value)

Output: 1388624

Here, the code enumerates over the reversed list of bytes, shifting each byte left by its position times 8 bits and adding it to the integer value. The final output is the integer representation of the list of bytes.

Bonus One-Liner Method 5: Using a generator expression with reduce

For those who love concise one-liners, Python’s reduce function combined with a generator expression provides a neat solution.

Here’s an example:

from functools import reduce
byte_list = [0x15, 0x02, 0x50]
int_value = reduce(lambda acc, b: (acc << 8) | b, byte_list)
print(int_value)

Output: 1388624

This method uses reduce to apply a lambda function across the list of bytes. The lambda shifts the accumulated value left by 8 bits and performs a bitwise OR with the current byte, yielding the integer value.

Summary/Discussion

  • Method 1: int.from_bytes() with Big-Endian. Efficient and Pythonic. Assumes the endianness is known.
  • Method 2: int.from_bytes() with Little-Endian. Similarly efficient and straightforward. Depends on correct byte order.
  • Method 3: Bitwise Operations. More manual but highly customizable. Good for understanding the underlying process.
  • Method 4: For-Loop and Multiplication. Simple to understand and implement. Can be less efficient for long lists of bytes.
  • Method 5: One-Liner with reduce. Compact and elegant. However, can be less readable for those not familiar with functional programming concepts.