Convert 4 bytes to integer using struct

Question

I have a microcontroller connected to my computer via I2C connection, which sends back 1 byte of data at a time. I am trying to send a 4-byte number to the python program. I receive it in an array of individual bytes like this [123,45,67,89].

I need to convert that back into an integer in python. I am trying to use struct.unpack to do this, but I cannot get the data format correct. I am trying to get it in the form:

struct.unpack("I",b'x12\x34\x56\x78)

I don't know how to get the 4 bytes into the form required by struct. I can convert the numbers to hex, but don't know how to string them together.

It is quite unclear what you are asking. Can you edit your question and elaborate more? — Billal BEGUERADJ
– Billal BEGUERADJ, Commented Apr 23, 2016 at 13:24

martineau · Accepted Answer · 2018-12-21 19:53:51Z

5

You could convert it to a bytearray and pass that to struct.unpack().

import struct

data = [123, 45, 67, 89]

# Show hex values of data.
print(list('%02x' % b for b in data))  # -> ['7b', '2d', '43', '59']

# Convert to 4 byte unsigned integer data interpreting data as being in 
# little-endian byte order.
value = struct.unpack("<I", bytearray(data))[0]
print(hex(value))  # -> 0x59432d7b

edited Dec 21, 2018 at 19:53

answered Apr 23, 2016 at 13:48

martineau

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