itertools.count
to create an iterator that returns an infinite sequence of numbersIn [2]: import itertools
In [3]: c = itertools.count()
In [4]: next(c)
Out[4]: 0
In [5]: next(c)
Out[5]: 1
In [6]: next(c)
Out[6]: 2
In [9]: test_email_generator = (f'diego{n}@example.com' for n in itertools.count())
In [10]: next(test_email_generator)
Out[10]: 'diego0@example.com'
In [11]: next(test_email_generator)
Out[11]: 'diego1@example.com'
In [12]: next(test_email_generator)
Out[12]: 'diego2@example.com'