Iterating over strings in Python - Step-by-Step Execution

Concept Flow - Iterating over strings

Start with string

↓

Set index = 0

↓

Check: index < length of string?

No→EXIT

Yes↓

Access character at index

↓

Use character (e.g., print)

↓

Increase index by 1

↩Back to Check

This flow shows how we start at the first character of a string and move through each character one by one until we reach the end.

Execution Sample

Python

word = "hello"
for char in word:
    print(char)

This code goes through each letter in the word "hello" and prints it on its own line.

Execution Table

Iteration	char	Action	Output
1	"h"	Print character	h
2	"e"	Print character	e
3	"l"	Print character	l
4	"l"	Print character	l
5	"o"	Print character	o
-	-	Loop ends	All characters printed

💡 After printing 'o', no more characters left, loop ends

Variable Tracker

Variable	Start	After 1	After 2	After 3	After 4	After 5	Final
char	None	"h"	"e"	"l"	"l"	"o"	None

Key Moments - 3 Insights

Why does the loop stop after printing 'o'?

The loop stops because it has gone through all characters in the string. As shown in the execution_table last row, there are no more characters left to process.

Is 'char' a number or a letter inside the loop?

Inside the loop, 'char' holds one letter (a string of length 1) from the word each time, as seen in the variable_tracker where 'char' changes to each letter.

Can we change characters inside the loop?

Strings are fixed in Python, so you cannot change characters directly. You can use the character for other actions, but not modify the original string.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of 'char' at iteration 3?

A "l"

B "e"

C "o"

D "h"

💡 Hint

Check the 'char' column in the execution_table at iteration 3

At which iteration does the loop finish printing all characters?

A 4

B 5

C 6

D 3

💡 Hint

Look at the exit_note and the last iteration row in execution_table

If the string was "hi", how many rows would the execution_table have before loop ends?

A 2

B 3

C 4

D 1

💡 Hint

Number of characters plus one exit row, see execution_table row count for 5-letter word

Concept Snapshot

Iterating over strings:
Use a for loop: for char in string:
Each loop step gives one character (char) from the string.
Loop runs until all characters are processed.
Strings are read-only; you can use but not change chars directly.

Full Transcript

This lesson shows how to go through each letter in a word using a for loop in Python. We start with the first letter, print it, then move to the next until we reach the end. The variable 'char' holds each letter one by one. The loop stops when there are no more letters. This is useful to read or use each character separately. Remember, strings cannot be changed inside the loop, only read.