Convert little endian string to integer

Question

I have read samples out of a wave file using the wave module, but it gives the samples as a string, it's out of wave so it's little endian (for example, \x00).

What is the easiest way to convert this into a python integer, or a numpy.int16 type? (It will eventually become a numpy.int16, so going directly there is fine).

Code needs to work on little endian and big endian processors.

Answer 1

Kevin Burke's answer to this question works great when your binary string represents a single short integer, but if your string holds binary data representing multiple integers, you will need to add an additional 'h' for each additional integer that the string represents.

For Python 2

Convert Little Endian String that represents 2 integers

import struct
iValues = struct.unpack("<hh", "\x00\x04\x01\x05")
print(iValues)

Output: (1024, 1281)

Convert Little Endian String that represents 3 integers

import struct
iValues = struct.unpack("<hhh", "\x00\x04\x01\x05\x03\x04")
print(iValues)

Output: (1024, 1281, 1027)

Obviously, it's not realistic to always guess how many "h" characters are needed, so:

import struct

# A string that holds some unknown quantity of integers in binary form
strBinary_Values = "\x00\x04\x01\x05\x03\x04"

# Calculate the number of integers that are represented by binary string data
iQty_of_Values = len(strBinary_Values)/2

# Produce the string of required "h" values
h = "h" * int(iQty_of_Values)

iValues = struct.unpack("<"+h, strBinary_Values)
print(iValues)

Output: (1024, 1281, 1027)

For Python 3

import struct

# A string that holds some unknown quantity of integers in binary form
strBinary_Values = "\x00\x04\x01\x05\x03\x04"

# Calculate the number of integers that are represented by binary string data
iQty_of_Values = len(strBinary_Values)/2

# Produce the string of required "h" values
h = "h" * int(iQty_of_Values)

iValues = struct.unpack("<"+h, bytes(strBinary_Values, "utf8"))
print(iValues)

Output: (1024, 1281, 1027)

Answer 2

The struct module converts packed data to Python values, and vice-versa.

>>> import struct
>>> struct.unpack("<h", "\x00\x05")
(1280,)
>>> struct.unpack("<h", "\x00\x06")
(1536,)
>>> struct.unpack("<h", "\x01\x06")
(1537,)

"h" means a short int, or 16-bit int. "<" means use little-endian.