Common string transformations in Python - Step-by-Step Execution

Concept Flow - Common string transformations

Start with original string

↓

Choose transformation

↓

Uppercase

↓

Output transformed string

↓

End

Start with a string, pick a transformation like uppercase, lowercase, or replace, then get the new string as output.

Execution Sample

Python

text = "Hello World"
upper_text = text.upper()
lower_text = text.lower()
replaced_text = text.replace("World", "Python")
print(upper_text)
print(lower_text)
print(replaced_text)

This code changes the string to uppercase, lowercase, and replaces a word, then prints each result.

Execution Table

Step	Variable	Operation	Result	Output
1	text	Assign original string	"Hello World"
2	upper_text	text.upper()	"HELLO WORLD"
3	lower_text	text.lower()	"hello world"
4	replaced_text	text.replace("World", "Python")	"Hello Python"
5	print(upper_text)	Output upper_text		HELLO WORLD
6	print(lower_text)	Output lower_text		hello world
7	print(replaced_text)	Output replaced_text		Hello Python

💡 All transformations done and printed, program ends.

Variable Tracker

Variable	Start	After 1	After 2	After 3	Final
text	"Hello World"	"Hello World"	"Hello World"	"Hello World"	"Hello World"
upper_text		"HELLO WORLD"	"HELLO WORLD"	"HELLO WORLD"	"HELLO WORLD"
lower_text			"hello world"	"hello world"	"hello world"
replaced_text				"Hello Python"	"Hello Python"

Key Moments - 2 Insights

Why does the original string 'text' not change after calling upper() or lower()?

Because string methods like upper() and lower() return a new string and do not modify the original string 'text' (see rows 2 and 3 in execution_table).

What happens if the word to replace is not found in the string?

The replace() method returns the original string unchanged. In the example, 'World' is found, so it changes (row 4). If not found, the result would be the same as 'text'.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of 'lower_text' after step 3?

A "Hello World"

B "hello world"

C "HELLO WORLD"

D "Hello Python"

💡 Hint

Check the 'Result' column for step 3 in execution_table.

At which step does the program output 'Hello Python'?

A Step 5

B Step 6

C Step 7

D Step 4

💡 Hint

Look at the 'Output' column in execution_table for the printed strings.

If we change text.replace("World", "Python") to text.replace("world", "Python"), what happens?

A The replaced_text remains "Hello World"

B The replaced_text becomes "Hello Python"

C An error occurs

D The replaced_text becomes "hello Python"

💡 Hint

Remember string replace is case-sensitive; check key_moments about replace behavior.

Concept Snapshot

Common string transformations in Python:
- Use str.upper() to get uppercase version
- Use str.lower() to get lowercase version
- Use str.replace(old, new) to replace parts
- These methods return new strings, original stays same
- Print results to see changes

Full Transcript

This example shows how to transform strings in Python. We start with a string 'Hello World'. We create new strings by changing all letters to uppercase with upper(), to lowercase with lower(), and by replacing the word 'World' with 'Python' using replace(). Each method returns a new string without changing the original. We print each result to see the changes. This helps understand how string transformations work step-by-step.