Fix Python – Convert bytes to int?

Question 1

I’m currently working on an encryption/decryption program and I need to be able to convert bytes to an integer. I know that:

bytes([3]) = b'\x03'

Yet I cannot find out how to do the inverse. What am I doing terribly wrong?

Question 2

Assuming you’re on at least 3.2, there’s a built in for this:

int.from_bytes( bytes, byteorder, *, signed=False )

…

The argument bytes must either be a bytes-like object or an iterable
producing bytes.

The byteorder argument determines the byte order used to represent the
integer. If byteorder is "big", the most significant byte is at the
beginning of the byte array. If byteorder is "little", the most
significant byte is at the end of the byte array. To request the
native byte order of the host system, use sys.byteorder as the byte
order value.

The signed argument indicates whether two’s complement is used to
represent the integer.

## Examples:
int.from_bytes(b'\x00\x01', "big")                         # 1
int.from_bytes(b'\x00\x01', "little")                      # 256

int.from_bytes(b'\x00\x10', byteorder='little')            # 4096
int.from_bytes(b'\xfc\x00', byteorder='big', signed=True)  #-1024

Question

Answer