Python Loops

Python Loops

In programming, we often need to execute a block of code multiple times. Instead of writing the same code repeatedly, we use loops.

Loops are control structures that allow for repeated execution of a code block based on a condition or by iterating over a sequence.

Conceptual Flow of a Loop:

1. Check a condition or get the next item from a sequence.
2. If the condition is true or items remain: Execute the loop body.
3. Go back to step 1.
4. If the condition is false or no items remain: Exit the loop and continue with the code after the loop.

Python provides two primary types of loops:

Loop Type	Description
while loop	Repeats a block of code as long as a given condition remains True. The condition is tested before each execution of the loop body.
for loop	Iterates over the items of any sequence (like a list, tuple, string, or range) or other iterable object, executing a block of code once for each item.
nested loops	You can place one loop inside another. This is useful for working with multi-dimensional data structures or complex iteration patterns.

Note: Python does not have a do..while loop construct found in some other languages, where the loop body is guaranteed to execute at least once before the condition is checked.

Loop Control Statements

Loop control statements alter the normal execution flow within loops:

Python supports the following control statements:

Control Statement	Description
break statement	Immediately terminates the current loop (the innermost loop if nested) and transfers execution to the statement following the loop.
continue statement	Skips the rest of the code inside the current iteration of the loop and proceeds to the next iteration (re-evaluating the condition in a while loop or getting the next item in a for loop).
pass statement	Acts as a null operation. It’s used when a statement is syntactically required but you don’t want any command or code to execute. It’s often used as a placeholder during development.

Example: while loop

count = 0
while count < 5:
    print(f"Count is: {count}")
    count += 1 # Important: Increment counter to avoid infinite loop

print("Loop finished!")

Example: for loop with range

for i in range(3): # range(3) generates numbers 0, 1, 2
    print(f"Iteration {i}")

print("Loop finished!")

Example: for loop with a list

fruits = ["apple", "banana", "cherry"]
for fruit in fruits:
    print(f"Current fruit: {fruit}")

print("Loop finished!")

Example: break statement

for i in range(10):
    if i == 5:
        print("Breaking loop")
        break # Exit the loop when i is 5
    print(f"i = {i}")

print("After the loop")

Example: continue statement

for i in range(5):
    if i == 2:
        print("Skipping iteration 2")
        continue # Skip the rest of this iteration
    print(f"Processing i = {i}")

print("After the loop")