Previous in yield operations - python

Question

Recently i have been using the 'yield' in python. And I find generator functions very useful. My query is that, is there something which could decrement the imaginative cursor in the generator object. Just how next(genfun) moves and outputs +i'th item in the container, i would like to know if there exists any function that may call upon something like previous(genfun) and moves to -1th item in the conatiner.

Actual Working

def wordbyword():
  words = ["a","b","c","d","e"]
  for word in words:
    yield word

getword = wordbyword()

next(getword)
next(getword)

Output's

a
b

What I would like to see and achieve is

def wordbyword():
  words = ["a","b","c","d","e"]
  for word in words:
    yield word

getword = wordbyword()

next(getword)
next(getword)
previous(getword)

Expected Output

a
b
a

This may sound silly, but is there someway there is this previous in generator, if not why is it so?. Why not we could decrement the iterator, or am I ignorant of an existing method, pls shower some light. What can be the closest way to implement what I have here in hand.

Answer 1

No there is no such function to sort of go back in a generator function. The reason is that Python does not store up the previous value in a generator function natively, and as it does not store it, it also cannot perform a recalculation.

For example, if your generator is a time-sensitive function, such as

def time_sensitive_generator():
    yield datetime.now()

You will have no way to recalculate the previous value in this generator function.

Of course, this is only one of the many possible cases that a previous value cannot be calculated, but that is the idea.

If you do not store the value yourself, it will be lost forever.