Python If, Elif, Else

Python Conditionals at a Glance

Until now, every line of code ran sequentially. The if, elif, and else statements let a program choose which code to run by evaluating comparison and logical expressions.

1. If, Elif, Else Infographic

Use this visual summary to review conditional syntax, program flow, examples, expected output, and common network automation use cases.

2. If

An if statement runs its indented block when its condition is True. Take a look at the code below:

ios_version = 15
if ios_version == 15:
    print("You have Cisco IOS version 15")
    print("Completed checking IOS version")

It shows this output:

You have Cisco IOS version 15
Completed checking IOS version

The variable ios_version stores the integer 15. The condition checks whether that value equals 15. Because it does, Python runs both indented print() calls.

If the condition does not match, Python skips the entire indented block:

ios_version = 12.4
if ios_version == 15:
    print("You have Cisco IOS version 15")
    print("Completed checking IOS version")

3. Shorthand If

When an if statement has a single action, you can write it on one line:

>>> if 90 > 75: print("CPU load is higher than threshold")
CPU load is higher than threshold

This compact form can save space, although the standard multi-line form is often easier to extend and review.

4. Nested If

A nested if places one condition inside another. The inner check runs only after the outer condition matches:

ios_version = 15
hostname = "SW1"

if "SW1" in hostname:
    print("This device is a switch")
    if ios_version == 15:
        print("Switch runs IOS version 15")

It shows this output:

This device is a switch
Switch runs IOS version 15

The outer condition matches the hostname, so Python prints the first message and evaluates the nested version check. The inner condition also matches, so it prints the second message.

5. Else

When the if condition is false, an else block provides the fallback action:

cpu_load = 75
if cpu_load > 90:
    print("CPU load is over 90%")
else:
    print("CPU load is OK!")

It shows this output:

CPU load is OK!

The CPU load is not greater than 90, so the if condition is false and Python runs the else block.

6. Shorthand Else

A conditional expression can place a simple if/else decision on one line:

>>> print("CPU load above threshold.") if 90 > 75 else print("CPU load OK")
CPU load above threshold.

This form is useful for one small choice. Prefer a normal multi-line statement when either branch needs several actions.

7. Elif

Use elif to test another condition when the earlier condition did not match. You can include multiple elif branches:

interface_message = "Interface Loopback1, changed state to administratively down"

if "Loopback0" in interface_message:
    print("Loopback0 has a shutdown command!")
elif "Loopback1" in interface_message:
    print("Loopback1 has a shutdown command!")
else:
    print("No loopback interface found.")

It shows this output:

Loopback1 has a shutdown command!

The first condition is false, but the elif condition matches. Python runs that branch and skips the final else.

8. Guided Practice

9. Conclusion

Python conditionals turn comparisons and logical expressions into decisions. Start with if, add elif for alternative tests, and use else when a fallback action is needed. Keep each block correctly indented, and use shorthand only when it remains easy to read.