numbers = [1,-2,-3,-4,5,6,-7,-8,9,10]

positive_number_count = 0

for num in numbers:

if num > 0:

positive_number_count+=1

print("Final count of positive number is :" , positive_number_count) #6

n = 10

sum_even = 0

for i in range(1,n+1):

if i % 2 == 0:

sum_even+=1

print("Sum of even number is:",sum_even)

number = 3

for i in range(1,11):

if i == 5:

continue

print(number , "x", i , '=', number*i)

input_str = "Python"

reversed_str = ""

for char in input_str:

reversed_str = char + reversed_str

print(reversed_str)

input_str = "teeter"

for char in input_str:

print(char)

if input_str.count(char) == 1:

print("char is :", char)

break

number = 5

factorial = 1

while number > 0:

factorial = factorial * number

number = number -1

print("Factorial is :", factorial)

while True:

number = int(input("Enter value b/w 1 and 10 "))

if 1 <= number <=10:

print("thanks")

break

else:

print("invalid number please again Enter")

number = 29

is_prime = True

if number > 1:

for i in range(2, number):

if (number % i) == 0:

is_prime = False

break

print(is_prime)

items = ["apple" , "banana" , "ornage" , "apple" , "mango"]

unique_item = set()

for item in items:

if item in unique_item:

print("Duplicate")

break

unique_item.add(item)

print(unique_item)

import time

wait_time = 1

max_retries = 5

attempts = 0

while attempts < max_retries:

print("Attempt", attempts + 1 , " wait time" , wait_time)

time.sleep(wait_time)

wait_time*=2

attempts+=1

This method returns an **iterator** object.

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3️⃣ ITERATORS — WHO DOES THE REAL WORK

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An iterator is an object that:

✅ Has a method `__iter__()` → returns itself

✅ Has a method `__next__()` → returns the next item

🚫 Raises `StopIteration` when all items are used

Example:

lst = [1, 2, 3]

itr = iter(lst)

print(next(itr)) # 1

print(next(itr)) # 2

print(next(itr)) # 3

print(next(itr)) # StopIteration Error

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4️⃣ HOW FOR LOOPS WORK INTERNALLY

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Code you write:

for item in myList:

print(item)

Python translates it behind the scenes to:

itr = iter(myList)

while True:

try:

item = next(itr)

print(item)

except StopIteration:

break

🔍 So `for` = `iter()` + repeated `next()`

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5️⃣ ITERABLE vs ITERATOR — WHAT’S THE DIFFERENCE?

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| Feature | Iterable | Iterator |

| ------------------ | -------- | -------- |

| Has **iter** | ✅ | ✅ |

| Has **next** | ❌ | ✅ |

| Remembers position | ❌ | ✅ |

Check using:

from collections.abc import Iterable, Iterator

print(isinstance([1,2,3], Iterable)) # True

print(isinstance([1,2,3], Iterator)) # False

print(isinstance(iter([1,2,3]), Iterator)) # True

⚠️ `iter(myList) is myList` → False

Because `iter()` returns a **new** iterator object.

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6️⃣ REAL-LIFE ANALOGY 🎧

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Iterable = Playlist → You can restart anytime

Iterator = Music Player → It plays one by one and remembers which song is playing

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7️⃣ FILE OBJECTS ARE ITERATORS 📂

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You can loop through files directly:

with open("file.txt") as f:

for line in f:

print(line)

Why? Because file objects implement both `__iter__()` and `__next__()`.

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8️⃣ CREATING CUSTOM ITERATORS 🛠️

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You can build your own iterator class using `__iter__()` and `__next__()`:

Example:

class CountUpto:

def __init__(self, max):

self.max = max

self.current = 1

def __iter__(self):

return self

def __next__(self):

if self.current > self.max:

raise StopIteration

val = self.current

self.current += 1

return val

for num in CountUpto(3):

print(num) # 1, 2, 3

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9️⃣ SUMMARY — KEY TAKEAWAYS ✅

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- `for` loops use `iter()` to get an iterator, and `next()` to get each value.

- `StopIteration` tells Python when to stop.

- Iterables (like list, str, file) do not have memory of position.

- Iterators remember where they left off.

- File objects are their own iterators.

- You can build custom iterators using Python classes.

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🔟 PRACTICE QUESTIONS 💬

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1. What does `iter()` return?

2. Why is `iter(myList) is myList` False?

3. What happens if we keep calling `next()` after the last item?

4. What exception tells Python to stop a loop?

5. What's the difference between an iterable and an iterator?

🎯 Tip: Mastering this helps you understand how loops, generators, comprehensions, and file I/O work at a deeper level!