I have 3 small ints (under 255) which can, therefore, be represented by a single byte.
I would like to create a larger int from that 3 bytes sequence.
For example, if those 3 ints where 1, 2 and 3, I would have:
00000001, 00000010 and 00000011
I then would like to get the int corresponding to:
000000010000001000000011, which according to a calculator would be the integer 66051 when converted to a decimal.
How can I go from 3 small ints to that final larger int in Python?
You can repeatedly left-shift a running total before adding another element:
>>> (((1 << 8) + 2) << 8) + 3
66051
This kind of iterated operation can be generalized to any number of integers using functools.reduce:
>>> from itertools import reduce
>>> reduce(lambda acc, x: (acc << 8) + x, [1,2,3]
66051
You can also use the struct module to pack the three 8-bit values into a single bytes value:
>>> import struct
>>> struct.pack('BBB", 1, 2, 3)
b'\x01\x02\x03'
which you can convert to an int value with
>>> int.from_bytes(b'\x01\x02\x03', 'big')
66051
You can use a bit-shift operator on an integer:
a = 0b01
b = 0b10
c = 0b11
d = (a << 16) + (b << 8) + c
print(f"{d:b}")
10000001000000011