Basic While Loop Structure¶
Here’s how a simple while loop looks:
count = 0
while count < 5:
print("Counting up:", count)
count += 1 # This is the same as count = count + 1
Counting up: 0 Counting up: 1 Counting up: 2 Counting up: 3 Counting up: 4
Combining While Loops with Lists¶
You can use while loops to process items in a list. Here’s a fun way to simulate a queue of tasks:
tasks = ["wash the car", "write the report", "pay bills", "post on social media"]
while tasks:
current_task = tasks.pop(0)
print("Handling task:", current_task)
Handling task: wash the car Handling task: write the report Handling task: pay bills Handling task: post on social media
Using a While Loop with a Break Statement¶
Sometimes you may want to exit a while loop ahead of time. break allows you to exit the loop, regardless of the loop's condition:
magic_number = 7
guess = 0
while True:
guess += 1
if guess == magic_number:
print("You guessed the magic number!")
break
### Output ###
# You guessed the magic number!
You guessed the magic number!
Using While Loops with the Continue Statement¶
The continue statement skips the current iteration and proceeds to the next iteration of the loop:
number = 0
while number < 10:
number += 1
if number % 2 == 0:
continue
print("Odd number:", number)
Odd number: 1 Odd number: 3 Odd number: 5 Odd number: 7 Odd number: 9
Infinite Loops¶
Be cautious with while loops because if the condition never becomes false, the loop will continue indefinitely. Here’s a simple, controlled example:
# Danger! Infinite loop!
# Uncomment to run at your own risk.
# while True:
# print("I'm stuck inside an infinite loop!")
Python For Loop¶
A for loop in Python iterates over a sequence (e.g., a list, tuple, string) and executes a block of code for each item in that sequence. It's especially handy when you know beforehand how many times the loop should run.
Basic For Loop Structure¶
Here’s a simple example of a for loop:
colors = ['red', 'blue', 'green', 'yellow']
for color in colors:
print(f"The color is {color}")
The color is red The color is blue The color is green The color is yellow
Using For Loops with Strings¶
For loops can be used to iterate through each character in a string:
greeting = "Hello"
for letter in greeting:
print(f"Give me a {letter}!")
Give me a H! Give me a e! Give me a l! Give me a l! Give me a o!
Looping Through Dictionaries¶
To loop through a dictionary, you can iterate over its keys, values, or key-value pairs:
pet_ages = {'cat': 2, 'dog': 5, 'parrot': 3}
for pet, age in pet_ages.items():
print(f"The {pet} is {age} years old.")
The cat is 2 years old. The dog is 5 years old. The parrot is 3 years old.
The range() Function¶
The range() function is often used in for loops when you need to perform an action a certain number of times:
for num in range(1, 6): # Starts at 1 and ends at 5, not including 6
print(f"Number {num}")
Number 1 Number 2 Number 3 Number 4 Number 5
Nested For Loops¶
For loops can be nested within one another to handle multi-dimensional data:
matrix = [
[1, 2, 3],
[4, 5, 6],
[7, 8, 9]
]
for row in matrix:
for num in row:
print(num, end=' ')
print() # for a new line after each row
1 2 3 4 5 6 7 8 9
Using break and continue¶
The break statement stops the loop before it has looped through all items. The continue statement skips the current iteration and proceeds to the next one:
# Example with break
for num in range(1, 10):
if num == 4:
break
print(num)
1 2 3
# Example with continue
for num in range(1, 10):
if num % 2 == 0:
continue
print(num)
1 3 5 7 9
Looping with an Index¶
Sometimes, you might need the index of the current item in the loop. You can use the enumerate() function:
heroes = ['Batman', 'Superman', 'Wonder Woman']
for index, hero in enumerate(heroes):
print(f"Hero {index + 1}: {hero}")
Hero 1: Batman Hero 2: Superman Hero 3: Wonder Woman