58. Custom Iterables with __iter__ and __next__

Here are 10 Python code snippets that demonstrate how to implement custom iterables using the __iter__ and __next__ methods:

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1. Simple Iterable Class

A basic class that defines an iterable object with a custom __iter__ and __next__ method.

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

    def __iter__(self):
        return self

    def __next__(self):
        if self.current <= 0:
            raise StopIteration
        self.current -= 1
        return self.current + 1

countdown = Countdown(5)
for number in countdown:
    print(number)
# Output: 5 4 3 2 1

This snippet defines a Countdown class that counts down from a starting number, printing each value in turn until it reaches 1.

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2. Fibonacci Sequence Iterable

Creating an iterable that generates Fibonacci numbers.

class Fibonacci:
    def __init__(self, limit):
        self.limit = limit
        self.a, self.b = 0, 1

    def __iter__(self):
        return self

    def __next__(self):
        if self.limit <= 0:
            raise StopIteration
        self.limit -= 1
        self.a, self.b = self.b, self.a + self.b
        return self.a

fib = Fibonacci(6)
for num in fib:
    print(num)
# Output: 1 1 2 3 5 8

This example defines an iterable that generates Fibonacci numbers up to a specified limit.

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3. Even Numbers Iterable

Creating an iterable for even numbers within a specified range.

class EvenNumbers:
    def __init__(self, start, end):
        self.start = start
        self.end = end
        self.current = start if start % 2 == 0 else start + 1

    def __iter__(self):
        return self

    def __next__(self):
        if self.current >= self.end:
            raise StopIteration
        current = self.current
        self.current += 2
        return current

evens = EvenNumbers(1, 10)
for num in evens:
    print(num)
# Output: 2 4 6 8

This code creates an iterable that generates even numbers between start and end.

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4. Reverse String Iterable

An iterable that iterates through a string in reverse.

class Reverse:
    def __init__(self, data):
        self.data = data
        self.index = len(data)

    def __iter__(self):
        return self

    def __next__(self):
        if self.index == 0:
            raise StopIteration
        self.index = self.index - 1
        return self.data[self.index]

reverse = Reverse("hello")
for char in reverse:
    print(char)
# Output: o l l e h

This snippet creates an iterable that iterates over a string in reverse order.

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5. Range-Like Iterable

Custom range class that behaves like Python’s built-in range.

class MyRange:
    def __init__(self, start, stop, step=1):
        self.start = start
        self.stop = stop
        self.step = step
        self.current = start

    def __iter__(self):
        return self

    def __next__(self):
        if self.current >= self.stop:
            raise StopIteration
        value = self.current
        self.current += self.step
        return value

my_range = MyRange(0, 5, 2)
for num in my_range:
    print(num)
# Output: 0 2 4

This defines a custom iterable that behaves like range(start, stop, step).

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6. Prime Numbers Iterable

An iterable that generates prime numbers.

class PrimeNumbers:
    def __init__(self, limit):
        self.limit = limit
        self.num = 2

    def __iter__(self):
        return self

    def __next__(self):
        while self.num <= self.limit:
            for i in range(2, self.num):
                if self.num % i == 0:
                    break
            else:
                prime = self.num
                self.num += 1
                return prime
            self.num += 1
        raise StopIteration

primes = PrimeNumbers(10)
for prime in primes:
    print(prime)
# Output: 2 3 5 7

This example creates an iterable that generates prime numbers up to a specified limit.

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7. Square Numbers Iterable

Creating an iterable that generates square numbers.

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

    def __iter__(self):
        return self

    def __next__(self):
        if self.current > self.end:
            raise StopIteration
        result = self.current ** 2
        self.current += 1
        return result

squares = Squares(1, 5)
for square in squares:
    print(square)
# Output: 1 4 9 16 25

This creates an iterable for square numbers from start to end.

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8. Character Repeated Iterable

An iterable that repeats a character multiple times.

class RepeatCharacter:
    def __init__(self, char, times):
        self.char = char
        self.times = times

    def __iter__(self):
        return self

    def __next__(self):
        if self.times <= 0:
            raise StopIteration
        self.times -= 1
        return self.char

repeater = RepeatCharacter('*', 5)
for char in repeater:
    print(char)
# Output: * * * * *

This iterable repeats a character a specified number of times.

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9. Matrix Row Iterator

Creating an iterable to traverse rows of a matrix.

class MatrixRowIterator:
    def __init__(self, matrix):
        self.matrix = matrix
        self.row = 0

    def __iter__(self):
        return self

    def __next__(self):
        if self.row >= len(self.matrix):
            raise StopIteration
        row = self.matrix[self.row]
        self.row += 1
        return row

matrix = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
iterator = MatrixRowIterator(matrix)
for row in iterator:
    print(row)
# Output: [1, 2, 3] [4, 5, 6] [7, 8, 9]

This snippet defines an iterable that iterates through the rows of a matrix.

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10. Random Number Iterable

An iterable that generates random numbers within a range.

import random

class RandomNumbers:
    def __init__(self, count, low, high):
        self.count = count
        self.low = low
        self.high = high

    def __iter__(self):
        return self

    def __next__(self):
        if self.count <= 0:
            raise StopIteration
        self.count -= 1
        return random.randint(self.low, self.high)

random_iterable = RandomNumbers(5, 1, 10)
for number in random_iterable:
    print(number)
# Output: Random numbers between 1 and 10

This creates an iterable that generates random numbers within a specified range for a given count.

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These examples demonstrate how to create custom iterables in Python by implementing the __iter__ and __next__ methods. This allows you to control the iteration behavior for any object and use it in for-loops or any other iterable context.