How to make a bytes object from a list of integers in Python 3

Just call the bytes constructor.

As the docs say:

… constructor arguments are interpreted as for bytearray().

And if you follow that link:

If it is an iterable, it must be an iterable of integers in the range 0 <= x < 256, which are used as the initial contents of the array.

So:

>>> list_of_values = [55, 33, 22]
>>> bytes_of_values = bytes(list_of_values)
>>> bytes_of_values
b'7!\x16'
>>> bytes_of_values == b'\x37\x21\x16'
True

Of course the values aren’t going to be \x55\x33\x22, because \x means hexadecimal, and the decimal values 55, 33, 22 are the hexadecimal values 37, 21, 16. But if you had the hexadecimal values 55, 33, 22, you’d get exactly the output you want:

>>> list_of_values = [0x55, 0x33, 0x22]
>>> bytes_of_values = bytes(list_of_values)
>>> bytes_of_values == b'\x55\x33\x22'
True
>>> bytes_of_values
b'U3"'