1.8 KiB
iterators
The iterator pattern allows you to perform some task on a sequence of items in turn. An iterator is responsible for the logic of iterating over each item and determining when the sequence has finished. Rust book
An itetarator it's usually related to some sort of lists, vectors or collection
of items, but the iterator can be anything that implements the interface. The
interaface depends on the language, but usually only needs a next(Self) -> Item
method that returns the next item to be acted upon.
The adventage of iterators is that you can use them with anything that accept
thems (kinda in the reusable side of programming), and modern standard
libraries implements patterns to use them like: forEach, map, sum, etc
Another common use case is to iterate on something indefinetly as long as it
continue to provide new items. For example you can implement a
PollingIterator that fetch data from a remote source until the source says
there's no more data:
class EmailPoll:
"""Iterator class that pools emails from the EmailService indefinetly."""
def __init__(self, service: EmailService, wait_time: int):
super(EmailPoll, self).__init__()
self.service = service
self.wait_time = wait_time
self.current_mails = self.service.fetch_emails()
def __iter__(self):
return self
def __next__(self):
while len(self.current_mails) == 0:
self.current_mails = self.service.fetch_emails()
if len(self.current_mails) == 0:
print(f"No new emails, waiting {self.wait_time}s")
sleep(self.wait_time)
return self.current_mails.pop(0)
email_service = EmailService()
for mail in EmailPoll(email_service, 3):
print(mail)