__iter__ — Easy Examples

Returns an iterator; makes the object usable in for loops

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Implementing __iter__

Basic implementation of __iter__ in a class.

python
class Countdown:
    def __init__(self, start):
        self.start = start

    def __iter__(self):
        n = self.start
        while n > 0:
            yield n
            n -= 1

for num in Countdown(5):
    print(num)

__iter__ returns an iterator; makes the object usable in for loops. Implementing it lets you customize how Python interacts with your objects.

__iter__ in action

Seeing __iter__ called by Python's built-in operations.

python
# How Python calls __iter__ automatically
class Demo:
    def __init__(self, value):
        self.value = value

    def __iter__(self):
        print(f"__iter__ was called!")
        return self

d = Demo(42)
# This triggers __iter__:
for x in d: break

Python automatically calls __iter__ when you use the corresponding operator or function on your object.

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