Python - How to edit hexadecimal file byte by byte

Question

I want to be able to open up an image file and extra the hexadecimal values byte-by-byte. I have no idea how to do this and googling "python byte editing" and "python byte array" didn't come up with anything, surprisingly. Can someone point me towards the library i need to use, specific methods i can google, or tutorials/guides?

Answer 1

The Hachoir framework is a set of Python library and tools to parse and edit binary files:

http://pypi.python.org/pypi/hachoir-core

It has knowledge of common file types, so this could just be what you need.

Answer 2

Python standard library has mmap module, which can be used to do exactly this. Take a look on the documentation for further information.

Answer 3

Depending on what you want to do it might be enough to open the file in binary mode and read the data with the normal file functions:

// load it
f = open("somefile", 'rb')
data = f.read()
f.close()

// do something with data
data.reverse()

// save it
f = open("somefile.new", 'wb')
f.write(data)
f.close()

Python doesn't really care if the data string contains "binary" or "text" data. If you just want to do simple modifications to a file of reasonable size this is probably good enough.

Answer 4

Check out the stuct module.

This module performs conversions between Python values and C structs represented as Python strings. It uses format strings (explained below) as compact descriptions of the lay-out of the C structs and the intended conversion to/from Python values. This can be used in handling binary data stored in files or from network connections, among other sources.