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Understanding Iterators in Python

What Are Iterators?

Technically, in Python, an iterator is an object that implements the iterator protocol, which consists of the following methods:

__iter__() : returns the iterator object itself, making it compatible with loops like for ;
__next__() : returns the next element in the sequence. When no elements remain, it raises a StopIteration exception to signal the end of traversal.

An iterator enables traversal of elements in an iterable (e.g., list or string) one at a time while keeping track of its position.

python

Note

An iterator is also an iterable because it implements the __iter__() method.

Not all iterables are iterators. For example, a list is iterable but not an iterator. When you pass it to the iter() function, you get an iterator that allows element-by-element traversal.

Building a Custom Iterator

This iterator generates a fixed number of random dice rolls and stops once all rolls are completed.


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import random

class FiniteDie:
    def __init__(self, num_rolls):
        """Initialize the iterator with a fixed number of rolls."""
        self.num_rolls = num_rolls
        self.current_roll = 0

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

    def __next__(self):
        """Generate the next dice roll or stop iteration."""
        if self.current_roll < self.num_rolls:
            self.current_roll += 1
            return random.randint(1, 6)
        raise StopIteration

# Using the FiniteDie iterator
num_rolls = 5
die_iterator = FiniteDie(num_rolls)

print(f"Rolling the die {num_rolls} times:")
for roll in die_iterator:
    print(f"Rolled: {roll}")

Iterator Exhaustion

Once an iterator is exhausted, it cannot be reused without recreating it. For example:


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numbers = [1, 2, 3, 4]
iterator = iter(numbers)

# First iteration
for num in iterator:
    print(num)  # Output: 1, 2, 3, 4

# Second iteration
for num in iterator:
    print(num)  # Output: Nothing, the iterator is exhausted.

Iterators can only be traversed once. To iterate again, a new iterator needs to be created.

Tarefa

Swipe to start coding

Complete the missing parts of the code to implement a custom iterator class for simulating an infinite die roller. The iterator should lazily generate random rolls of a six-sided die and stop after 10 rolls.

The __iter__() method allows an object to be used as an iterator.
The __next__() method produces the next random die roll (a number between 1 and 6).
Create an instance of the InfiniteDie class, which represents the die roller.
Use a for loop with enumerate() to roll the die lazily. Stop after 10 rolls using an if condition and the break statement.

Solução

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Seção 6. Capítulo 2

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Understanding Iterators in Python

What Are Iterators?

Technically, in Python, an iterator is an object that implements the iterator protocol, which consists of the following methods:

__iter__() : returns the iterator object itself, making it compatible with loops like for ;
__next__() : returns the next element in the sequence. When no elements remain, it raises a StopIteration exception to signal the end of traversal.

An iterator enables traversal of elements in an iterable (e.g., list or string) one at a time while keeping track of its position.

python

Note

An iterator is also an iterable because it implements the __iter__() method.

Not all iterables are iterators. For example, a list is iterable but not an iterator. When you pass it to the iter() function, you get an iterator that allows element-by-element traversal.

Building a Custom Iterator

This iterator generates a fixed number of random dice rolls and stops once all rolls are completed.


              123456789101112131415161718192021222324252627
            
import random

class FiniteDie:
    def __init__(self, num_rolls):
        """Initialize the iterator with a fixed number of rolls."""
        self.num_rolls = num_rolls
        self.current_roll = 0

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

    def __next__(self):
        """Generate the next dice roll or stop iteration."""
        if self.current_roll < self.num_rolls:
            self.current_roll += 1
            return random.randint(1, 6)
        raise StopIteration

# Using the FiniteDie iterator
num_rolls = 5
die_iterator = FiniteDie(num_rolls)

print(f"Rolling the die {num_rolls} times:")
for roll in die_iterator:
    print(f"Rolled: {roll}")

Iterator Exhaustion

Once an iterator is exhausted, it cannot be reused without recreating it. For example:


              12345678910
            
numbers = [1, 2, 3, 4]
iterator = iter(numbers)

# First iteration
for num in iterator:
    print(num)  # Output: 1, 2, 3, 4

# Second iteration
for num in iterator:
    print(num)  # Output: Nothing, the iterator is exhausted.

Iterators can only be traversed once. To iterate again, a new iterator needs to be created.

Tarefa

Swipe to start coding

The __iter__() method allows an object to be used as an iterator.
The __next__() method produces the next random die roll (a number between 1 and 6).
Create an instance of the InfiniteDie class, which represents the die roller.
Use a for loop with enumerate() to roll the die lazily. Stop after 10 rolls using an if condition and the break statement.

Solução

Mude para o desktop para praticar no mundo realContinue de onde você está usando uma das opções abaixo

Tudo estava claro?

Obrigado pelo seu feedback!

Seção 6. Capítulo 2

Mude para o desktop para praticar no mundo realContinue de onde você está usando uma das opções abaixo