py2 vs py3: zlib.adler32/crc32

[Karsten Hilbert]

Hi all,

I am unsure how to solve: I use adler32/crc32 to generate integer values from data
for setting up an advisory lock in PostgreSQL.

The PG function pg_try_advisory_lock()

  https://www.postgresql.org/docs/12/functions-admin.html#FUNCTIONS-ADVISORY-LOCKS

takes two PG ints which are defined as:

   integer 	4 bytes 	typical choice for integer 	-2147483648 to +2147483647

Now, in Py > 2.5 zlib.adler32/crc32 will return suitable integers.

However, in Py3 the return range has been changed to

   The return value is unsigned and in the range [0, 2**32-1] regardless of platform.

which will overflow the PostgreSQL function.

Is there a way to convert/modify/shift the py3 value such that it shows the
same representation as the py2 value ?   What I am looking for is:

  v2 = py2.zlib.adler32(data)
  v3 = some_magic(py3.zlib.adler32(data))
  if v2 == v3:
     print('same')

I am sure there's something obvious with struct/<</& and
such like which I am overlooking.

Note that I can't simply do

   v2 = py2.zlib.adler32(data) & 0xffffffff

because that can overflow the PostgreSQL integer. I think I need
the reverse, in a sense, but I am too dense, ATM.

Thanks for any help,
Karsten