Impara The Iterator Protocol | Python Iterators

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In Python, the iterator protocol is a set of methods that allows objects to be iterated over, making them compatible with constructs like for loops. The two essential methods involved are __iter__ and __next__. When you use a for loop on an object, Python internally calls the object's __iter__ method to retrieve an iterator. This iterator must have a __next__ method, which returns the next item in the sequence each time it is called. When there are no more items, __next__ must raise a StopIteration exception to signal the end of the sequence.


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class SquaresIterator:
    # Initialize with the number of squares to generate
    def __init__(self, limit):
        self.limit = limit
        self.current = 0   

    # Return the iterator object (itself)
    def __iter__(self):
        return self

    # Return the next square, or stop if done
    def __next__(self):
        if self.current < self.limit:
            # Calculate square
            result = self.current ** 2  
            
            # Move to next number
            self.current += 1           
            return result
        # If no more items
        else:
            raise StopIteration  


for square in SquaresIterator(5):
    print(square)

`init` - Setup Phase

When the iterator is created it receives a:

limit → how many numbers to generate;
It sets current = 0 → the starting point;
It prepares everything needed for iteration.

`iter` - Making It Iterable

Returns self (the object itself);
This is what allows you to use it in a for loop.

`next` - Producing Values

This method runs every time the loop asks for the next item:

If current < limit:
- Calculate current²;
- Increase current by 1;
- Return the result.
If current ≥ limit:
- Raise StopIteration to stop the loop automatically.

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Sezione 5. Capitolo 3

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Sezione 5. Capitolo 3

The Iterator Protocol

__init__ - Setup Phase

__iter__ - Making It Iterable

__next__ - Producing Values

`init` - Setup Phase

`iter` - Making It Iterable

`next` - Producing Values