✅ Iterator using __iter__() and __next__()
class Counter:
    def __init__(self, start, end):
        self.current = start
        self.end = end

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

    def __next__(self):
        # Returns the next value or raises StopIteration
        if self.current <= self.end:
            num = self.current
            self.current += 1
            return num
        else:
            raise StopIteration

# Using the iterator
c = Counter(1, 5)

for num in c:
    print(num)  # Output: 1 2 3 4 5
✅ Generator Function using yield
def countdown(n):
    while n > 0:
        yield n    # Pause and resume here
        n -= 1

# Using the generator
for i in countdown(5):
    print(i)  # Output: 5 4 3 2 1
✅ Generator Expression
# Similar to list comprehension but lazy
squares = (x*x for x in range(5))

for num in squares:
    print(num)  # Output: 0 1 4 9 16
✅ Generator vs List (Memory Comparison)
import sys

lst = [x for x in range(10000)]
gen = (x for x in range(10000))

print(sys.getsizeof(lst))  # Larger memory
print(sys.getsizeof(gen))  # Much smaller memory