Python Iterators
External
Internal
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
Iterators and Dictionaries
Applying iter() to a dictionary returns a key iterator.
d = {'k1': 'v1', 'k2': 'v2'}
i = iter(d)
keys = set()
keys.add(next(i))
keys.add(next(i))
assert len(keys) == 2
assert 'k1' in keys
assert 'k2' in keys
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
The Standard Library itertools module has a collection of generators for many common data algorithms.
TODO:
- To explore.
- Process: https://learning.oreilly.com/library/view/python-for-data/9781098104023/ch03.html#:-:text=itertools%20module