Custom Iterable Structures

Custom iterables let your structure work like a list in a for loop.

Why this matters

In real code you may build:

• stream readers
• custom collections
• data pipelines

Example: custom range-like structure

class MyRange:
    def __init__(self, start, end):
        self.start = start
        self.end = end

    def __iter__(self):
        self.cur = self.start
        return self

    def __next__(self):
        if self.cur >= self.end:
            raise StopIteration
        val = self.cur
        self.cur += 1
        return val

for x in MyRange(3, 7):
    print(x)

Graph: iterator lifecycle

flowchart LR
  A[__iter__] --> B[__next__]
  B --> C[Yield value]
  C --> B
  B --> D[StopIteration]

Remember

• iter returns iterator object
• next returns next item
• StopIteration ends the loop