Python Conditional Basics

Every program needs to make decisions — whether it’s checking if a user is old enough to vote, verifying login details, or deciding if a stock should be bought or sold.
In Python, we make such decisions using conditional statements.

In this blog, you’ll learn:

• What conditional statements are
• The if, elif, and else keywords
• Comparison and logical operators
• Nested and shorthand conditionals
• Real-world examples

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🧠 1. What Are Conditional Statements?

Conditional statements allow your program to execute certain blocks of code only if specific conditions are met.

For example:

“If it’s raining, take an umbrella. Else, go outside.”

In Python, we use:

• if – to check a condition
• elif – to check another condition if the previous one fails
• else – to handle all other cases

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🧩 2. The if Statement

The simplest conditional in Python.

age = 18

if age >= 18:
    print("You are eligible to vote.")

Output:

You are eligible to vote.

Here’s what happens:

• Python checks if age >= 18.
• If True, it executes the print() statement.
• If False, it skips that block.

Note: Python uses indentation (spaces) to define code blocks — not braces {} like other languages.

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🔁 3. The if...else Statement

Sometimes you want one thing to happen if the condition is true, and something else if it’s false.

num = 10

if num % 2 == 0:
    print("Even number")
else:
    print("Odd number")

Output:

Even number

Here, the program checks if num is divisible by 2.
If not, it executes the else block.

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🔄 4. The if...elif...else Chain

Use elif (short for else if) when you need to check multiple conditions.

marks = 75

if marks >= 90:
    print("Grade: A")
elif marks >= 75:
    print("Grade: B")
elif marks >= 60:
    print("Grade: C")
else:
    print("Grade: D")

Output:

Grade: B

Here:

• Python checks each condition in order.
• Once a condition is True, it runs that block and skips the rest.

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⚙️ 5. Comparison Operators in Python

Comparison operators are used to compare values in conditions.

Operator	Description	Example	Result
==	Equal to	5 == 5	True
!=	Not equal to	5 != 3	True
>	Greater than	10 > 5	True
<	Less than	3 < 8	True
>=	Greater than or equal	5 >= 5	True
<=	Less than or equal	4 <= 2	False

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🧩 6. Logical Operators

You can combine multiple conditions using logical operators:

Operator	Meaning	Example	Result
and	True if both conditions are true	x > 0 and x < 10	True if x between 0 and 10
or	True if at least one condition is true	x > 10 or x == 5	True if any condition is true
not	Reverses the condition	not(x > 10)	True if x <= 10

Example:

age = 25
country = "India"

if age > 18 and country == "India":
    print("Eligible for Indian voter ID.")

Output:

Eligible for Indian voter ID.

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🔁 7. Nested if Statements

You can put one if inside another — this is called a nested condition.

age = 20
citizen = "Indian"

if age >= 18:
    if citizen == "Indian":
        print("Eligible to vote in India.")
    else:
        print("Not an Indian citizen.")
else:
    print("Not old enough to vote.")

Output:

Eligible to vote in India.

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⚡ 8. Shorthand if Statement (One-Liner)

Python allows compact single-line conditionals.

x = 10
print("Positive") if x > 0 else print("Non-positive")

Output:

Positive

This is useful for quick, simple checks.

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🎯 9. Real-World Example — Checking Login Access

username = "admin"
password = "1234"

if username == "admin" and password == "1234":
    print("Access granted.")
else:
    print("Access denied.")

Output:

Access granted.

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🧮 10. Example — Number Classification

Let’s build a program that checks whether a number is positive, negative, or zero.

num = float(input("Enter a number: "))

if num > 0:
    print("Positive number")
elif num < 0:
    print("Negative number")
else:
    print("Zero")

Output (if user enters -5):

Negative number

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🧠 11. Example — Leap Year Checker

year = int(input("Enter a year: "))

if (year % 4 == 0 and year % 100 != 0) or (year % 400 == 0):
    print("Leap year")
else:
    print("Not a leap year")

Output:

Leap year

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🔍 12. Common Mistakes to Avoid

❌ Missing indentation:

if True:
print("Hello")  # ❌ Wrong

✅ Correct:

if True:
    print("Hello")

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🧾 Summary

Concept	Description	Example
if	Executes if condition is true	if x > 0:
if...else	Executes one of two blocks	if x > 0: ... else: ...
elif	Checks multiple conditions	if...elif...else
and, or, not	Combine multiple conditions	if x > 0 and y < 5:
Nested if	One if inside another	if x > 0: if y > 0:
Shorthand if	Single-line conditional	"Yes" if True else "No"

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💡 Key Takeaways

✅ Conditional statements help programs make decisions
✅ Python uses indentation to define code blocks
✅ Use and, or, not for combining conditions
✅ Always test your logic with different inputs

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🧱 Example Challenge for You

Try writing a Python program that:

• Takes a user’s marks as input
• Prints whether the user passed, failed, or got distinction