Why use iterator classes vs iterative variable?

Python Help
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1

I am new to python and object-oriented programing.
Why use iterator classes vs iterative variable?

Is the way class (object-oriented) just more modular?

iterative example:

for i in n:
i = i +1
print("Hi ", i)

2

I am new to python and object-oriented programing.
Why use iterator classes vs iterative variable?

I’m not sure I understand this question.

Is the way class (object-oriented) just more modular?

iterative example:

for i in n:
i = i +1
print("Hi ", i)

This is very odd. What is in “n”? A list? What does the “i = i + 1” do?

A class is for implementing things. If you’ve already got an iterator,
or some iterable thing like a list, you don’t need to implement a new
class. You’d write a class if you needed to make some special kind of
iterator not already available.

If this doesn’t help you, can you:

  • provide your “iterative variable” example more ompletely, for example
    a something which runs (that would need to define what is in “n” at
    least).
  • describe what you mean by an “iterator class”?

Some terminology:

  • an iterable: something with a iter method, which returns an
    iterator

  • an iterator: something with a next method, which returns the next
    value in the series of values

An iterable class defines one method: iter to return an iterator
over whatever the class instance embodies.

An iterator has a next method to return the next value in the
iteration, and usually also an iter which returns itself.

Often people just define iter as a generator function, which
automatically returns a generator object which has these methods:

class RangeLike:

    def __init__(self, value):
        self.value = value

    def __iter__(self):
        for i in range(self.value):
            yield i

This is a simple class which just stores a number and when you iterate
over it, yields values 0…(value-1) inclusively, like this:

R = RangeLike(4)
for i in R:
    print(i)

The for-loop calls “iter(R)” to obtain an iterator for R, and that is a
generator function. It looks like a regular function, but instead of
returning a single value it "yield"s multiple values. Calling it gets
you a “generator object”, which is an iterator (something which yields a
series of values).

The mechanism of the for-loop looks like this:

R = RangeLike(4)
R_iter = iter(R)
while True:
    try:
        i = next(R_iter)
    except StopIteration:
        break
    print(i)

So the for-loop calls iter(R), getting an iterator we keep as “R_iter”;
that calls R.iter() to get that iterator.

Then the loop itself calls next(R_iter) to get the next value for “i”;
each such call calls R_iter.next().

When R_iter came from a generator function, that runs the function until
it issues a “yield” command. Then next time you call next(), the
function continues running until it again issues a “yield” command.

Cheers,
Cameron Simpson cs@cskk.id.au