For loop execution model in Python - Step-by-Step Execution

Concept Flow - For loop execution model

Start

↓

Get next item from iterable

↓

Is item available?

No→Exit loop

Yes↓

Execute loop body with item

↓

Repeat: Get next item

The for loop gets each item from a list (or other iterable), runs the loop body with that item, and repeats until no items remain.

Execution Sample

Python

for num in [1, 2, 3]:
    print(num)

This code prints each number in the list one by one.

Execution Table

Iteration	num value	Condition (item available?)	Action	Output
1	1	Yes	Print num=1	1
2	2	Yes	Print num=2	2
3	3	Yes	Print num=3	3
4	None	No	Exit loop

💡 No more items in the list, loop ends

Variable Tracker

Variable	Start	After 1	After 2	After 3	Final
num	None	1	2	3	3

Key Moments - 3 Insights

Why does the loop stop after printing 3?

Because after the third item, there are no more items in the list. The condition 'item available?' becomes No, so the loop exits (see execution_table row 4).

Is the variable 'num' still set after the loop ends?

Yes, after the loop finishes, 'num' retains the value of the last item, 3 (see variable_tracker final value is 3).

What happens if the list is empty?

The loop body never runs because the condition 'item available?' is No immediately, so it exits without printing anything.

Visual Quiz - 3 Questions

Look at the execution table, what is the value of 'num' during iteration 2?

A 1

B 2

C 3

D None

💡 Hint

Check the 'num value' column in execution_table row for iteration 2

At which iteration does the loop condition become false?

A Iteration 4

B Iteration 1

C Iteration 3

D Never

💡 Hint

Look at the 'Condition (item available?)' column in execution_table

If the list was empty, what would the execution table show for iteration 1?

A num=1, Condition Yes, Print num=1

B num=0, Condition Yes, Print num=0

C num=None, Condition No, Exit loop

D No iteration rows at all

💡 Hint

Think about what happens when no items are available at the start (see key_moments)

Concept Snapshot

For loop syntax:
for variable in iterable:
    body

Behavior:
- Gets each item from iterable
- Runs body with item
- Stops when no items left

Key rule: Loop variable changes each iteration to next item.

Full Transcript

A for loop in Python takes each item from a list or other iterable one by one. It assigns the item to a variable, then runs the code inside the loop using that variable. This repeats until there are no more items. For example, looping over [1, 2, 3] prints each number. The loop stops after the last item because the condition to get a new item fails. The loop variable retains the value of the last item after the loop ends. If the list is empty, the loop body never runs.