Python Iterators

External

• https://docs.python.org/3/glossary.html#term-iterator

Internal

• Python Language

TODO

TO PROCESS PyOOP "The Iterator Pattern" + "Iterators" + "The iterator protocol"

Overview

An iterator instance represents a stream of data.

The iterator instances are created from iterable objects with the built-in function iter():

l = ['a', 'b', 'c']
i = iter(l)

Once created, repeated invocations of the iterator's __next__() method, or by passing it to the built-in function next(), return successive items in the stream:

assert next(i) == 'a'
assert next(i) == 'b'
assert next(i) == 'c'

When no more data are available a StopIteration exception is raised instead. At this point, the iterator object is exhausted and any further calls to its __next__() method just raise StopIteration again. There's no has_next() method that tests the availability of a next item without consuming it. Unavailability of a next item is tested by checking the StopIteration exception.

try:
    while True:
        arg = next(i)
        print(arg)
except StopIteration:
    pass

If you are OK to always consume the next item, the end of the iterator can be tested with:

...
next(i, None) is not None

Removing an Element while Iterating

It does not seem that Python iterators can remove elements while iterating, similar to Java's Iterator.remove(). To achieve the same behavior, use a list and remove an element while iterating the list.

itertools

To explore