Why Python Hashes Differ Across Sessions

Python’s hash() function can return different values for the same input in different sessions. For example:

$ python -c "print(hash('hi'))"
5037238841261226463
$ python -c "print(hash('hi'))"
4385354407237833037

This is by design, to enhance security and prevent certain types of collision attacks. You can control this behavior by setting the PYTHONHASHSEED environment variable. If you set PYTHONHASHSEED to ‘0’, Python will use the same seed value every time it starts up, and the hash() function will return consistent values across sessions. However, this is generally not recommended, as it reduces the security of the hash function.

If you want to hash arbitrary objects deterministically, you can use the hashlib standard module.