Searching and replacing text in Python - Mini Project: Build & Apply

Searching and replacing text

📖 Scenario: Imagine you have a short story saved as a string. You want to find and replace certain words to make the story more fun or correct mistakes.

🎯 Goal: You will create a program that searches for a specific word in a story and replaces it with another word.

📋 What You'll Learn

Create a string variable with the story text

Create variables for the word to find and the word to replace it with

Use the string replace() method to change the word

Print the updated story

💡 Why This Matters

🌍 Real World

Text editing and processing is common in writing apps, chat programs, and data cleaning.

💼 Career

Knowing how to search and replace text helps in software development, data analysis, and content management.

1

Create the story text

Create a string variable called story with this exact text: 'The cat sat on the mat.'

Python

# Create the story string variable
# Your code here

Hint

Use single or double quotes to create the string.

2

Set the word to find and replace

Create a variable called word_to_find and set it to 'cat'. Then create a variable called word_to_replace and set it to 'dog'.

Python

story = 'The cat sat on the mat.'
# Create word_to_find and word_to_replace variables
# Your code here

Hint

Use simple assignment to create these variables.

3

Replace the word in the story

Create a new variable called new_story that uses story.replace(word_to_find, word_to_replace) to replace the word.

Python

story = 'The cat sat on the mat.'
word_to_find = 'cat'
word_to_replace = 'dog'
# Replace word_to_find with word_to_replace in story
# Your code here

Hint

Use the replace() method on the story string.

4

Print the updated story

Write a print() statement to display the new_story variable.

Python

story = 'The cat sat on the mat.'
word_to_find = 'cat'
word_to_replace = 'dog'
new_story = story.replace(word_to_find, word_to_replace)
# Print the new_story
# Your code here

Hint

Use print(new_story) to show the changed story.

Practice

1. What does the replace method do in Python strings?

easy

A. It finds a specified substring and replaces it with another substring.

B. It deletes a substring from the string permanently.

C. It changes the original string directly without creating a new one.

D. It counts how many times a substring appears in the string.

Solution

1. Step 1: Understand the purpose of replace()

   The replace method searches for a substring and replaces it with another substring.

2. Step 2: Check if it modifies original string

   Strings are immutable in Python, so replace returns a new string without changing the original.

3. Final Answer:

   It finds a specified substring and replaces it with another substring. -> Option A

4. Quick Check:

   replace() = find and change substring [OK]

Hint: Remember: replace returns new string, original stays same [OK]

Common Mistakes:

• Thinking replace changes the original string
• Confusing replace with delete or count methods
• Assuming replace modifies in-place

2. Which of the following is the correct syntax to replace all occurrences of 'cat' with 'dog' in a string text?

easy

A. text.replace('cat', 'dog', all=True)

B. text.replace('cat', 'dog')

C. text.replace('cat' -> 'dog')

D. text.replace('cat', 'dog', count=0)

Solution

1. Step 1: Recall replace() syntax

   The correct syntax is string.replace(old, new[, count]), where old and new are strings.

2. Step 2: Analyze options

   text.replace('cat', 'dog') matches the correct syntax. Options A, B, and D use invalid syntax or parameters.

3. Final Answer:

   text.replace('cat', 'dog') -> Option B

4. Quick Check:

   replace(old, new) syntax = text.replace('cat', 'dog') [OK]

Hint: Use replace(old, new) without extra keywords [OK]

Common Mistakes:

• Using arrows or keywords inside replace()
• Adding unsupported parameters like all=True
• Confusing parameter order

3. What will be the output of this code?

text = 'apple apple apple'
new_text = text.replace('apple', 'orange', 2)
print(new_text)

medium

A. 'apple orange orange'

B. 'orange orange orange'

C. 'orange orange apple'

D. 'apple apple orange'

Solution

1. Step 1: Understand replace with count

   The third argument 2 limits replacements to first two occurrences.

2. Step 2: Apply replacements

   First two 'apple' become 'orange', last remains 'apple'. Result: 'orange orange apple'.

3. Final Answer:

   'orange orange apple' -> Option C

4. Quick Check:

   replace with count=2 changes first two only [OK]

Hint: Count limits how many replacements happen [OK]

Common Mistakes:

• Replacing all occurrences ignoring count
• Replacing from the end instead of start
• Miscounting number of replacements

4. The following code tries to replace 'blue' with 'red' but causes an error. What is the error?

text = 'blue sky'
text.replace('blue', 'red', 'all')
print(text)

medium

A. SyntaxError due to wrong quotes

B. AttributeError because replace is not a string method

C. No error, prints 'red sky'

D. TypeError because 'all' is not an integer for count

Solution

1. Step 1: Check replace() parameters

   The third parameter must be an integer count, but 'all' is a string.

2. Step 2: Identify error type

   Passing a string instead of int causes a TypeError at runtime.

3. Final Answer:

   TypeError because 'all' is not an integer for count -> Option D

4. Quick Check:

   replace count must be int, not string [OK]

Hint: Count parameter must be integer, not string [OK]

Common Mistakes:

• Using strings instead of integers for count
• Expecting replace to modify original string
• Confusing error types

5. You have a paragraph stored in text. You want to replace only the first 3 occurrences of the word 'error' with 'issue'. Which code snippet correctly does this?

hard

A. new_text = text.replace('error', 'issue', 3)

B. new_text = text.replace('error', 'issue', count=3)

C. new_text = text.replace('error', 'issue', '3')

D. new_text = text.replace('error', 'issue')[:3]

Solution

1. Step 1: Use replace with count parameter

   To replace only first 3 occurrences, use replace(old, new, count) with count=3.

2. Step 2: Analyze options

   new_text = text.replace('error', 'issue', 3) uses correct syntax. new_text = text.replace('error', 'issue', count=3) uses invalid keyword argument. new_text = text.replace('error', 'issue', '3') passes count as string. new_text = text.replace('error', 'issue')[:3] slices string incorrectly.

3. Final Answer:

   new_text = text.replace('error', 'issue', 3) -> Option A

4. Quick Check:

   replace(old, new, 3) replaces first 3 only [OK]

Hint: Use third argument as integer count for limited replacements [OK]

Common Mistakes:

• Using keyword count instead of positional argument
• Passing count as string instead of int
• Trying to slice string after replace