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Functional Programming Concepts in Python

bookThe Iterator Protocol

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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)
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__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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Which of the following is required for an object to be considered iterable in Python?

Select the correct answer

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Section 5. Chapter 3

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Section 5. Chapter 3
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