Python Conditions & Loops

Conditions and loops are fundamental constructs in Python that allow you to control the flow of your program.

1. Conditional Statements

Conditional statements allow you to execute code only if certain conditions are met.

1.1 if Statement

x = 10

            if x > 5:
                print("x is greater than 5")
            

1.2 if-else Statement

x = 3

            if x > 5:
                print("x is greater than 5")
            else:
                print("x is 5 or less")
            

1.3 elif Statement

Used for multiple conditions:

x = 10

            if x > 15:
                print("x is greater than 15")
            elif x > 5:
                print("x is greater than 5 but <= 15")
            else:
                print("x is 5 or less")
            

1.4 Nested Conditions

x = 10
            y = 20

            if x > 5:
                if y > 15:
                    print("Both conditions are true")
            

2. Loops

Loops are used to execute a block of code repeatedly until a condition is met.

2.1 for Loop

Iterates over a sequence (list, tuple, string, range, etc.):

fruits = ["apple", "banana", "cherry"]

            for fruit in fruits:
                print(fruit)

            # Using range()
            for i in range(5):
                print(i)  # Prints 0 to 4
            

2.2 while Loop

Repeats as long as a condition is True:

count = 0

            while count < 5:
                print(count)
                count += 1
            

2.3 break Statement

Stops the loop prematurely:

for i in range(10):
                if i == 5:
                    break
                print(i)  # Prints 0 to 4
            

2.4 continue Statement

Skips the current iteration and continues with the next:

for i in range(5):
                if i == 2:
                    continue
                print(i)  # Prints 0,1,3,4
            

2.5 else with Loops

An optional else block can run after the loop finishes normally (not via break):

for i in range(3):
                print(i)
            else:
                print("Loop completed")  # Runs after loop finishes
            

3. Nested Loops

Loops inside loops:

for i in range(3):
                for j in range(2):
                    print(f"i={i}, j={j}")
            

4. Best Practices

• Keep loop bodies small and simple for readability.
• Prefer for loops over while when the number of iterations is known.
• Avoid deep nesting of loops and conditions to maintain clarity.

5. Interview Questions

Q1. Difference between if-else and elif?

elif allows checking multiple conditions without writing multiple nested if-else blocks.

Q2. Can a while loop run forever?

Yes, if its condition never becomes False. Example: while True:

Q3. What is the purpose of break and continue?

break exits a loop immediately; continue skips the current iteration.

Q4. Can loops have else block?

Yes, the else block executes if the loop finishes normally (not via break).