Concatenate two 32 bit int to get a 64 bit long in Python

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
>>>

This should do it:

(x << 32) + y

foo = <some int>
bar = <some int>

foobar = (foo << 32) + bar