Python Loops

Python Loops at a Glance

A loop is an instruction that executes code multiple times. Each pass through the loop is called an iteration.

1. Python Loops Infographic

Use this visual guide to review loop types, flow diagrams, code examples, break, continue, and common network automation uses.

2. For Loop

The for loop runs a defined amount of times before it ends. This is useful when you want to execute code a specific number of times. You can also use a for loop to go through each item in a sequence, such as the items in a list.

devices = ["R1", "R2", "SW1", "FW1"]

for device in devices:
    print("Device:", device)

It shows this output:

Device: R1
Device: R2
Device: SW1
Device: FW1

The loop performs one iteration for each device in the list. The variable device holds the current item during each pass.

3. While Loop

The while loop repeats itself and does not end until a certain condition is met. Each time an iteration ends, Python checks the condition again. When the condition is false, the loop ends; otherwise, the code in the loop runs again.

count = 1

while count <= 5:
    print("Count:", count)
    count += 1

It shows this output:

Count: 1
Count: 2
Count: 3
Count: 4
Count: 5

Updating count is essential: it eventually makes the condition false. If a while loop's condition never changes, the loop can continue indefinitely.

4. Conclusion

Loops are useful when you want to execute the same line or block of code multiple times, or when you want to process multiple items such as the devices in a list. A for loop handles a known number of repetitions or a sequence, while a while loop continues until its condition changes.