Loops are a fundamental part of programming, allowing you to repeat a block of code as long as a condition is true. In Python, the while loop is one of two main loop types (the other is for).
This tutorial covers:
-
How
whileloops work -
Syntax and flow
-
Examples with explanations
-
Controlling loops with
breakandcontinue -
Common pitfalls and best practices
-
A complete example at the end
✅ What Is a while Loop?
A while loop repeats code as long as a condition remains true. It's useful when you don't know in advance how many times you'll need to loop.
Syntax
while condition:
# code block
As long as condition is True, Python executes the code block.
Example 1: Basic Loop
count = 1
while count <= 5:
print("Count:", count)
count += 1
Output:
Count: 1
Count: 2
Count: 3
Count: 4
Count: 5
count += 1increasescounteach time, eventually making the conditionFalseto stop the loop.
Example 2: Infinite Loop (Be Careful!)
while True:
print("This will run forever!")
This loop will never stop unless:
-
You use
break(see below) -
You interrupt it manually (Ctrl+C)
⛔ Breaking Out of a Loop – break
Use break to exit a loop early, even if the condition is still True.
while True:
user_input = input("Enter 'q' to quit: ")
if user_input == 'q':
break
print("You entered:", user_input)
Skipping Iterations – continue
Use continue to skip the current iteration and go to the next one.
x = 0
while x < 5:
x += 1
if x == 3:
continue # Skip printing 3
print(x)
Output:
1
2
4
5
else Clause with while
The else block runs after the loop ends normally (not via break).
x = 0
while x < 3:
print(x)
x += 1
else:
print("Loop finished without break.")
Common Patterns
Waiting for Correct Input
password = ""
while password != "admin123":
password = input("Enter password: ")
print("Access granted")
Counting or Accumulating
total = 0
number = 1
while number <= 5:
total += number
number += 1
print("Sum:", total)
Common Pitfalls
| Mistake | Why It Happens | Solution |
|---|---|---|
| Infinite loop | Condition never becomes False |
Update loop variables inside loop |
Forgetting : after while |
SyntaxError | Always add : |
| Improper indentation | IndentationError | Indent all loop content properly |
Using = instead of == |
Assignment instead of comparison | Use == in condition |
Tips and Best Practices
-
Use counters or variables to control the loop.
-
Avoid infinite loops unless intentional.
-
Use
breaksparingly to avoid unreadable logic. -
For known-length iteration, prefer a
forloop. -
Keep conditions clear and simple.
Complete Example: Number Guessing Game
import random
secret_number = random.randint(1, 10)
guess = None
while guess != secret_number:
guess = int(input("Guess a number (1-10): "))
if guess < secret_number:
print("Too low!")
elif guess > secret_number:
print("Too high!")
print("You guessed it!")
Summary Table
| Feature | Description |
|---|---|
| Loop type | while loop |
| Terminates when | Condition becomes False |
| Keywords used | while, break, continue, else |
| Use case | Unknown number of iterations |
| Risks | Infinite loop if condition never changes |
What's Next?
After learning while loops, explore:
-
forloops for fixed iterations -
range()function -
Nested loops
-
Using loops with
lists,dictionaries, andfiles
Tips and Tricks
What is pass in Python?
Python | Pass Statement
The pass statement is used as a placeholder for future code. It represents a null operation in Python. It is generally used for the purpose of filling up empty blocks of code which may execute during runtime but has yet to be written.
def myfunction():
pass
How can you generate random numbers?
Python | Generate random numbers
Python provides a module called random using which we can generate random numbers. e.g: print(random.random())
We have to import a random module and call the random() method as shown below:
import random
print(random.random())
The random() method generates float values lying between 0 and 1 randomly.
To generate customized random numbers between specified ranges, we can use the randrange() method
Syntax: randrange(beginning, end, step)
import random
print(random.randrange(5,100,2))
What is lambda in Python?
Python | Lambda function
A lambda function is a small anonymous function. This function can have any number of parameters but, can have just one statement.
Syntex:
lambda arguments : expression
a = lambda x,y : x+y
print(a(5, 6))
It also provides a nice way to write closures. With that power, you can do things like this.
def adder(x):
return lambda y: x + y
add5 = adder(5)
add5(1) #6
As you can see from the snippet of Python, the function adder takes in an argument x and returns an anonymous function, or lambda, that takes another argument y. That anonymous function allows you to create functions from functions. This is a simple example, but it should convey the power lambdas and closures have.
What is swapcase() function in the Python?
Python | swapcase() Function
It is a string's function that converts all uppercase characters into lowercase and vice versa. It automatically ignores all the non-alphabetic characters.
string = "IT IS IN LOWERCASE."
print(string.swapcase())
How to remove whitespaces from a string in Python?
Python | strip() Function | Remove whitespaces from a string
To remove the whitespaces and trailing spaces from the string, Python provides a strip([str]) built-in function. This function returns a copy of the string after removing whitespaces if present. Otherwise returns the original string.
string = " Python "
print(string.strip())
What is the usage of enumerate() function in Python?
Python | enumerate() Function
The enumerate() function is used to iterate through the sequence and retrieve the index position and its corresponding value at the same time.
lst = ["A","B","C"]
print (list(enumerate(lst)))
#[(0, 'A'), (1, 'B'), (2, 'C')]
Can you explain the filter(), map(), and reduce() functions?
Python | filter(), map(), and reduce() Functions
- filter() function accepts two arguments, a function and an iterable, where each element of the iterable is filtered through the function to test if the item is accepted or not.
>>> set(filter(lambda x:x>4, range(7))) # {5, 6}
-
map() function calls the specified function for each item of an iterable and returns a list of result
>>> set(map(lambda x:x**3, range(7))) # {0, 1, 64, 8, 216, 27, 125}
-
reduce() function reduces a sequence pair-wise, repeatedly until we arrive at a single value..
>>> reduce(lambda x,y:y-x, [1,2,3,4,5]) # 3Let’s understand this:
2-1=1
3-1=2
4-2=2
5-2=3Hence, 3.
What is a namedtuple?
Python | namedtuple
A namedtuple will let us access a tuple’s elements using a name/label. We use the function namedtuple() for this, and import it from collections.
>>> from collections import namedtuple
#format
>>> result=namedtuple('result','Physics Chemistry Maths')
#declaring the tuple
>>> Chris=result(Physics=86,Chemistry=92,Maths=80)
>>> Chris.Chemistry
# 92
Write a code to add the values of same keys in two different dictionaries and return a new dictionary.
We can use the Counter method from the collections module
from collections import Counter
dict1 = {'a': 5, 'b': 3, 'c': 2}
dict2 = {'a': 2, 'b': 4, 'c': 3}
new_dict = Counter(dict1) + Counter(dict2)
print(new_dict)
# Print: Counter({'a': 7, 'b': 7, 'c': 5})
Python In-place swapping of two numbers
Python | In-place swapping of two numbers
>>> a, b = 10, 20
>>> print(a, b)
10 20
>>> a, b = b, a
>>> print(a, b)
20 10
Reversing a String in Python
Python | Reversing a String
>>> x = 'PythonWorld'
>>> print(x[: : -1])
dlroWnohtyP
Python join all items of a list to convert into a single string
Python | Join all items of a list to convert into a single string
>>> x = ["Python", "Online", "Training"]
>>> print(" ".join(x))
Python Online Training
python return multiple values from functions
Python | Return multiple values from functions
>>> def A():
return 2, 3, 4
>>> a, b, c = A()
>>> print(a, b, c)
2 3 4
Python Print String N times
Python | Print String N times
>>> s = 'Python'
>>> n = 5
>>> print(s * n)
PythonPythonPythonPythonPython
Python check the memory usage of an object
Python | Check the memory usage of an object
>>> import sys
>>> x = 100
>>> print(sys.getsizeof(x))
28
