Infinate Number Generator

[Larz60+]

There's probably already something like this in collections, but I wanted to write one, so came up with this.
I found it useful for a test case.
to use, instantiate class NumberGenerator like myctr = NumberGenerator(12, 8).numgen
now each time you call myctr() it returns a number starting at 12, and increments by 8
of course you can do the sane thing with range, if in a loop, this one does not require the loop.

class NumberGenerator:
    def __init__(self, start=0, increment=1):
        self.start = start
        self.increment = increment
        self.current_num = start
    
    def numgen(self):
        retval = self.current_num
        self.current_num += self.increment
        return retval


def testit():
    # test1 create a counter1 counts starting at 15 incrementing by 2
    c1 = NumberGenerator(15, 2).numgen
    for x in range(10):
        print(f'c1: {c1()}')
    print()
    # test2 create another counter2 starts at 25 decrementing by -3
    c2 = NumberGenerator(25, -3).numgen
    for x in range(10):
        print(f'c2: {c2()}')
    
    # test 3 one more time for each counter
    print(f'\nc1 again: {c1()}')
    print(f'c2 again: {c2()}\n')

if __name__ == '__main__':
    testit()

output:

Output:
c1: 15
c1: 17
c1: 19
c1: 21
c1: 23
c1: 25
c1: 27
c1: 29
c1: 31
c1: 33

c2: 25
c2: 22
c2: 19
c2: 16
c2: 13
c2: 10
c2: 7
c2: 4
c2: 1
c2: -2

c1 again: 35
c2 again: -5

[micseydel]

This definitely be done with a built-in

Output:
>>> from itertools import count
>>> c3 = count(25, -3).__next__
>>> for x in range(10):
...     print(f"c3: {c3()}")
... 
c3: 25
c3: 22
c3: 19
c3: 16
c3: 13
c3: 10
c3: 7
c3: 4
c3: 1
c3: -2

[wavic]

How about this:

>>> numgen = lambda start, stop, step: (num for num in range(start, stop, step))
>>> for n in numgen(10, 0, -2):
...     print(n)
... 
10
8
6
4
2
>>> 

[micseydel]

How about this:

Can't you just inline the range() call there? The lambda and comprehension are just indirection wrapping it.

[wavic]

It's not a comprehension but generator expression. I am using lambda because range requires at least one parameter and I can't pass it just using an expression alone. Like: (n for n in range())

[micseydel]

Comprehensions can be of the list or generator variety (or for that matter sets and dictionaries in modern Python).

Let me show you what I meant:

Output:
>>> for n in range(10, 0, -2):
...     print(n)
... 
10
8
6
4
2

It produces the same output as yours, minus the comprehension, minus the lambda. I don't understand what benefit there is to including them when you can skip them without any issues.

EDIT: to clarify, the link I have here says that the original docs didn't say "generate comprehension" but calls for people to use the term. I don't want to dig into this particular terminology argument, but I think it's a reasonable term, I think Ned is a good Python authority, and the rest of my points about indirection still stand.

[wavic]

Yes, this implementation is totally useless because range produces one value at a time.