Question

I want to generate 64 bits long int to serve as unique ID’s for documents.

One idea is to combine the user’s ID, which is a 32 bit int, with the Unix timestamp, which is another 32 bits int, to form an unique 64 bits long integer.

A scaled-down example would be:

Combine two 4-bit numbers 0010 and 0101 to form the 8-bit number 00100101.

1. Does this scheme make sense?
2. If it does, how do I do the “concatenation” of numbers in Python?

Answer 1

Left shift the first number by the number of bits in the second number, then add (or bitwise OR – replace + with | in the following examples) the second number.

result = (user_id << 32) + timestamp

With respect to your scaled-down example,

>>> x = 0b0010
>>> y = 0b0101
>>> (x << 4) + y
37
>>> 0b00100101
37
>>>