Searching and replacing text in Python - Step-by-Step Execution

Concept Flow - Searching and replacing text

Start with original text

↓

Search for target substring

↓

Is target found?

No→End, return original text

Yes↓

Replace target with new substring

↓

Return modified text

↓

End

The program starts with the original text, searches for a target substring, replaces it if found, and returns the modified text.

Execution Sample

Python

text = "Hello world"
new_text = text.replace("world", "Python")
print(new_text)

This code replaces the word 'world' with 'Python' in the text and prints the result.

Execution Table

Step	Action	Evaluation	Result
1	Set text variable	text = "Hello world"	text = "Hello world"
2	Call replace method	text.replace("world", "Python")	"Hello Python"
3	Assign replaced text to new_text	new_text = "Hello Python"	new_text = "Hello Python"
4	Print new_text	print(new_text)	Output: Hello Python
5	End of program	No more code	Program ends

💡 Program ends after printing the replaced text.

Variable Tracker

Variable	Start	After replace	Final
text	"Hello world"	"Hello world"	"Hello world"
new_text	undefined	"Hello Python"	"Hello Python"

Key Moments - 2 Insights

Why does the original 'text' variable not change after replace?

Because the replace method returns a new string and does not modify the original string. See execution_table step 2 and variable_tracker where 'text' stays the same.

What happens if the target substring is not found?

The replace method returns the original string unchanged. The program would print the original text. This is implied in the concept_flow where 'No' branch returns original text.

Visual Quiz - 3 Questions

Look at the execution_table at step 2, what is the result of the replace method?

A "Hello world"

B "Hello Python"

C "Python world"

D "Hello"

💡 Hint

Check the 'Result' column in execution_table row with Step 2.

At which step is the new_text variable assigned the replaced string?

A Step 3

B Step 1

C Step 2

D Step 4

💡 Hint

Look at the 'Action' column in execution_table where new_text is assigned.

If the target substring 'world' was not in text, what would new_text be after replace?

A "Hello Python"

B "Python"

C "Hello world"

D "" (empty string)

💡 Hint

Recall that replace returns original string if target not found, see key_moments explanation.

Concept Snapshot

Searching and replacing text in Python:
- Use str.replace(old, new) to replace substrings.
- It returns a new string; original string stays unchanged.
- If old substring not found, original string is returned.
- Assign result to a new variable or overwrite.
- Example: new_text = text.replace("old", "new")

Full Transcript

This example shows how to search and replace text in Python using the replace method. The program starts with a string variable 'text' containing 'Hello world'. It calls text.replace("world", "Python") which returns a new string 'Hello Python'. This new string is assigned to 'new_text'. The original 'text' variable remains unchanged because strings are immutable in Python. Finally, the program prints 'Hello Python'. If the target substring is not found, replace returns the original string unchanged. This process is shown step-by-step in the execution table and variable tracker.