How to Use if else in Python

What you’ll build or solve

You’ll write if, elif, and else blocks that make decisions based on conditions.

When this approach works best

This approach works best when you:

• Validate input before you use it, like checking a number is in range.
• Choose between actions, like showing a different message for new vs returning users.
• Handle multiple outcomes, like grading scores or mapping status codes to labels.

Prerequisites

• Python 3 installed
• You know what variables are
• You can run a .py file or use the Python REPL

Step-by-step instructions

1) Write a basic if block

An if block runs only when its condition is true.

temperature=28

iftemperature>25:
print("It is warm")

2) Add an else for the fallback case

Use else when you want a default path if the condition is false.

is_member=False

ifis_member:
price=8
else:
price=10

print(price)

What to look for:

• The condition after if must be followed by :.
• The block must be indented.

3) Use elif for multiple conditions

Use elif when you have more than two branches.

score=82

ifscore>=90:
grade="A"
elifscore>=80:
grade="B"
elifscore>=70:
grade="C"
else:
grade="D"

print(grade)

Python checks each condition in order and stops at the first one that is true.

4) Combine conditions with and, or, and not

You can build more precise checks by combining boolean logic.

Option A (most common): require multiple conditions with and

age=20
has_id=True

ifage>=18andhas_id:
print("Allowed")
else:
print("Not allowed")

Option B (alternative): accept either condition with or

is_admin=False
is_owner=True

ifis_adminoris_owner:
print("You can edit")
else:
print("Read-only")

Use not to invert a condition:

is_banned=False

ifnotis_banned:
print("Welcome")

5) Compare values the Python way

Most conditions use comparison operators:

• == equal
• != not equal
• <, >, <=, >=

country="US"

ifcountry=="US":
print("United States")
else:
print("Other")

For membership checks, use in:

role="editor"
allowed= {"admin","editor"}

ifroleinallowed:
print("Access granted")

What to look for:

Use == for equality checks. A single = is for assignment.

6) Use nested if blocks when you need a second decision

Nesting works when one decision depends on another. Keep nesting shallow so your code stays readable.

user= {"name":"Sam","active":True}

ifuser["active"]:
ifuser["name"]:
print("Active user with a name")
else:
print("Active user missing a name")
else:
print("Inactive user")

Examples you can copy

1) Clamp a number into a range

value=125

ifvalue<0:
value=0
elifvalue>100:
value=100

print(value)

2) Parse simple command choices

choice="save"

ifchoice=="save":
print("Saving...")
elifchoice=="load":
print("Loading...")
else:
print("Unknown command")

3) Validate signup input

This checks conditions in order and stops at the first failure.

username="jo"
password="abc12345"

iflen(username)<3:
print("Username too short")
eliflen(password)<8:
print("Password too short")
else:
print("Looks good")

Common mistakes and how to fix them

Mistake 1: Using = instead of == in a condition

You might write:

x=10

ifx =10:
print("Ten")

Why it breaks:

= assigns a value. Conditions need == to compare.

Correct approach:

x=10

ifx==10:
print("Ten")

Mistake 2: Forgetting the colon or indentation

You might write:

age=18

ifage>=18
print("Allowed")

Why it breaks:

Python uses : and indentation to define the block.

Correct approach:

age=18

ifage>=18:
print("Allowed")

Mistake 3: Writing impossible logic with or

You might write:

day="sat"

ifday=="sat"or"sun":
print("Weekend")

Why it breaks:

"sun" is always truthy, so the condition always passes.

Correct approach:

day="sat"

ifday=="sat"orday=="sun":
print("Weekend")

Or better:

ifdayin {"sat","sun"}:
print("Weekend")

Troubleshooting

If you see IndentationError, check that you used consistent indentation, usually 4 spaces, inside the if block.

If you see SyntaxError at the if line, check for a missing : at the end of the condition.

If your if block never runs, print the values you compare and confirm types match, like "10" (string) vs 10 (int).

If a condition seems backwards, rewrite it with a simpler comparison first, then add and or or after it works.

Quick recap

• Use if for a single condition, and else for the fallback.
• Use elif for multiple branches.
• Combine checks with and, or, and not.
• Use == for comparisons, and in for membership checks.
• Watch colons and indentation, Python treats them as syntax.