Question

I want to convert an 32-byte (although I might need other lengths) integer to a bytes object in python. Is there a clean and simple way to do this?

Answer 1

I’m guessing you need a 32-bit integer, and big-endian to boot:

>>> from ctypes import c_uint32
>>> l = c_uint32(0x12345678)
>>> bytes(l)
b'xV4\x12'

There is c_uint8, c_uint16 and c_uint64 as well. For longer ints you need to make it manually, using divmod(x, 256).

>>> def bytify(v):
...   v, r = divmod(v, 256)
...   yield r
...   if v == 0:
...      raise StopIteration
...   for r in bytify(v):
...     yield r
... 
>>> [x for x in bytify(0x12345678)]
[120, 86, 52, 18]
>>> bytes(bytify(0x12345678))
b'xV4\x12
>>> bytes(bytify(0x123456789098765432101234567890987654321))
b'!Ce\x87\t\x89gE#\x01!Ce\x87\t\x89gE#\x01'