If/Else Statements

if/else statements let your code make decisions. Python evaluates a condition — if it is True, one block of code runs; if it is False, a different block runs.

Basic if / else

device_status = "online"

if device_status == "online":
    print("Device is online. Proceed with configuration.")
else:
    print("Device is offline. Unable to perform configuration.")

Adding elif for Multiple Conditions

elif stands for "else if." It lets you chain multiple conditions. Python checks each one from top to bottom and executes only the first one that is True:

x = 20

if x < 10:
    print("x is less than 10")
elif x < 30:
    print("x is less than 30 but not less than 10")
else:
    print("x is 30 or more")

- You can have as many elif blocks as you need. - The else at the end is a "catch-all" — it runs only if none of the conditions above were True. - Both elif and else are optional. A lone if is valid on its own.

Real-World Example — Classify an IP Address

ip_address = "192.168.1.1"

if ip_address.startswith("192.168"):
    print(f"{ip_address} is private — 192.168.0.0/16 range")
elif ip_address.startswith("10"):
    print(f"{ip_address} is private — 10.0.0.0/8 range")
elif ip_address.startswith("172.16"):
    print(f"{ip_address} is private — 172.16.0.0/12 range")
else:
    print(f"{ip_address} is not a private IP address")

Indentation — How Python Defines Code Blocks

Python does not use curly braces {} like many other languages. Instead, it uses indentation (4 spaces per level) to define which lines belong to which block. This is strict — incorrect indentation is a syntax error:

x = 10

if x > 5:
    print("Inside the if block")      # indented → belongs to the if
    print("Still inside the block")   # indented → also belongs to the if

print("Outside the if block")         # NOT indented → always runs

Example of what breaks:

# ❌ This causes an IndentationError
if x > 5:
print("x is greater than 5")   # must be indented!