What are the advantages and disadvantages of functions that do not possess idempotency?

Functions that are not idempotent, when called repeatedly with the same arguments, may change state or return different results.

Advantages:

• Allow implementing operations that change state, such as writing to a database or generating unique values.
• Flexibility in behavior, which is necessary for many business logics.

Disadvantages:

• More difficult to debug and test, as repeated calls may lead to different results.
• Can cause side effects, complicating predictability and reusability.
• In distributed systems, they complicate handling of repeated requests (e.g., during network failures).

Example of a non-idempotent function:

counter = 0
def increment():
    global counter
    counter += 1
    return counter

Each call to increment() returns a new value, the function changes state, and it is not idempotent.