Endianness of integers in Python

python integer endianness
G Gordon Worley III picture G Gordon Worley III · Sep 9, 2009 · Viewed 33.2k times · Source

I'm working on a program where I store some data in an integer and process it bitwise. For example, I might receive the number 48, which I will process bit-by-bit. In general the endianness of integers depends on the machine representation of integers, but does Python do anything to guarantee that the ints will always be little-endian? Or do I need to check endianness like I would in C and then write separate code for the two cases?

I ask because my code runs on a Sun machine and, although the one it's running on now uses Intel processors, I might have to switch to a machine with Sun processors in the future, which I know is big-endian.

Answer

Alex Martelli picture Alex Martelli · Sep 9, 2009

Python's int has the same endianness as the processor it runs on. The struct module lets you convert byte blobs to ints (and viceversa, and some other data types too) in either native, little-endian, or big-endian ways, depending on the format string you choose: start the format with @ or no endianness character to use native endianness (and native sizes -- everything else uses standard sizes), '~' for native, '<' for little-endian, '>' or '!' for big-endian.

This is byte-by-byte, not bit-by-bit; not sure exactly what you mean by bit-by-bit processing in this context, but I assume it can be accomodated similarly.

For fast "bulk" processing in simple cases, consider also the array module -- the fromstring and tostring methods can operate on large number of bytes speedily, and the byteswap method can get you the "other" endianness (native to non-native or vice versa), again rapidly and for a large number of items (the whole array).

Related questions

How to byte-swap a 32-bit integer in python?

Take this example: i = 0x12345678 print("{:08x}".format(i)) # shows 12345678 i = swap32(i) print("{:08x}".format(i)) # should print 78563412 What would be the swap32-function()? Is there a way to byte-swap an int in python, ideally with built-in tools?

Read More
How do I parse a string to a float or int?

In Python, how can I parse a numeric string like "545.2222" to its corresponding float value, 545.2222? Or parse the string "31" to an integer, 31? I just want to know how to parse a float str to a float, and (separately) an int …

Read More
Converting integer to string in Python

I want to convert an integer to a string in Python. I am typecasting it in vain: d = 15 d.str() When I try to convert it to string, it's showing an error like int doesn't have any attribute called str.

Read More