Generators & Iterators

✅ What is an Iterator?

An iterator is something you can loop through one item at a time.

🔁 Think of it like:

A TV remote — every time you press the "Next" button (__next__()), it gives you the next channel (value).

💡 In Python:

Any object with two methods:

• __iter__() – returns the iterator object itself

• __next__() – returns the next item, or throws an error if no more items

🔹 Example:

numbers = [1, 2, 3]
it = iter(numbers)

print(next(it))  # 1
print(next(it))  # 2
print(next(it))  # 3

✅ What is a Generator?

A generator is a special function that behaves like an iterator.

But instead of returning all values at once, it yields them one at a time.

🔁 Think of it like:

A water filter that gives one drop at a time when needed — instead of filling an entire bucket.

🔧 Generator Example (Improved):

def countdown(n):
    while n > 0:
        yield n  # Pause and give the current value
        n -= 1   # Then continue

# Use the generator
for i in countdown(5):
    print(i)

5
4
3
2
1

✅ Why Use a Generator?

🔍 Real-world Example – Reading Large File Line-by-Line

def read_file_lines(filepath):
    with open(filepath, "r") as f:
        for line in f:
            yield line.strip()  # yield each line without loading whole file

for line in read_file_lines("large_file.txt"):
    print(line)

🔁 Summary Table: