String cleaning (strip, lower, replace) in Data Analysis Python - Mini Project: Build & Apply

String cleaning (strip, lower, replace)

📖 Scenario: You work in a small online store. You receive customer feedback with messy text data. The text has extra spaces, mixed uppercase and lowercase letters, and some unwanted characters.Cleaning this text helps you analyze customer opinions better.

🎯 Goal: Clean a list of customer feedback strings by removing extra spaces, converting all letters to lowercase, and replacing unwanted characters.

📋 What You'll Learn

Create a list of feedback strings with exact given values

Create a variable for the unwanted character to replace

Use string methods strip(), lower(), and replace() to clean each feedback

Print the cleaned list of feedback strings

💡 Why This Matters

🌍 Real World

Cleaning text data is important in customer feedback analysis, social media monitoring, and preparing data for machine learning.

💼 Career

Data analysts and data scientists often clean messy text data before analysis or building models.

1

Create the feedback list

Create a list called feedback with these exact strings: ' Great product! ', 'Loved it!!', 'Not good...', ' Could be better ', 'Worst experience!!!'

Data Analysis Python

# Create the list called feedback with the exact strings
# Your code here

Hint

Use square brackets [] to create a list and include the exact strings with quotes.

2

Set the unwanted character

Create a variable called unwanted_char and set it to the exclamation mark character '!'

Data Analysis Python

feedback = ['  Great product!  ', 'Loved it!!', 'Not good...', '  Could be better  ', 'Worst experience!!!']
# Create the variable unwanted_char and set it to '!'
# Your code here

Hint

Use single quotes to assign the exclamation mark character to unwanted_char.

3

Clean the feedback strings

Create a new list called cleaned_feedback using a list comprehension. For each string f in feedback, apply strip(), then lower(), then replace all unwanted_char with an empty string ''.

Data Analysis Python

feedback = ['  Great product!  ', 'Loved it!!', 'Not good...', '  Could be better  ', 'Worst experience!!!']
unwanted_char = '!'
# Create cleaned_feedback list using list comprehension and string methods
# Your code here

Hint

Use a list comprehension with for f in feedback. Chain the string methods in order: strip(), lower(), then replace().

4

Print the cleaned feedback

Print the variable cleaned_feedback to display the cleaned list of feedback strings.

Data Analysis Python

feedback = ['  Great product!  ', 'Loved it!!', 'Not good...', '  Could be better  ', 'Worst experience!!!']
unwanted_char = '!'
cleaned_feedback = [f.strip().lower().replace(unwanted_char, '') for f in feedback]
# Print the cleaned_feedback list
# Your code here

Hint

Use print(cleaned_feedback) to show the cleaned list.

Practice

1. What does the strip() method do to a string in Python?

easy

A. Replaces parts of the string with new text

B. Removes spaces from the start and end of the string

C. Converts all characters to lowercase

D. Splits the string into a list of words

Solution

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

   The strip() method removes whitespace characters from the beginning and end of a string.

2. Step 2: Compare with other methods

   lower() changes case, replace() changes parts of the string, and splitting creates lists, so they do not match strip().

3. Final Answer:

   Removes spaces from the start and end of the string -> Option B

4. Quick Check:

   strip() = remove spaces [OK]

Hint: strip() cleans edges of spaces fast [OK]

Common Mistakes:

• Thinking strip() changes case
• Confusing strip() with replace()
• Assuming strip() splits strings

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

easy

A. text.lower('cat', 'dog')

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

C. text.strip('cat', 'dog')

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

Solution

1. Step 1: Identify the correct method for replacement

   The replace() method is used to change parts of a string by specifying the old and new substrings.

2. Step 2: Check the syntax

   The syntax is string.replace(old, new). So, to replace 'cat' with 'dog', it is text.replace('cat', 'dog').

3. Final Answer:

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

4. Quick Check:

   replace(old, new) = correct syntax [OK]

Hint: replace(old, new) swaps text parts [OK]

Common Mistakes:

• Swapping old and new strings
• Using strip() or lower() instead of replace()
• Wrong method call syntax

3. What will be the output of the following code?

text = '  Hello World  '
cleaned = text.strip().lower().replace('world', 'there')
print(cleaned)

medium

A. 'hello there'

B. 'hello world'

C. ' hello there '

D. 'Hello There'

Solution

1. Step 1: Apply strip() to remove spaces

   The original string has spaces at start and end. strip() removes them, so string becomes 'Hello World'.

2. Step 2: Apply lower() to convert to lowercase

   Converts 'Hello World' to 'hello world'.

3. Step 3: Apply replace() to change 'world' to 'there'

   Replaces 'world' with 'there', resulting in 'hello there'.

4. Final Answer:

   'hello there' -> Option A

5. Quick Check:

   strip + lower + replace = 'hello there' [OK]

Hint: Chain strip, lower, replace for clean text [OK]

Common Mistakes:

• Forgetting strip() removes spaces
• Not converting to lowercase before replace
• Replacing with wrong case

4. The following code is intended to clean a string by removing spaces and converting to lowercase, but it causes an error. What is the problem?

text = '  Data Science  '
cleaned = text.strip.lower()
print(cleaned)

medium

A. replace() method is missing

B. lower() should be called before strip()

C. strip() is missing parentheses

D. print() is used incorrectly

Solution

1. Step 1: Identify method call syntax

   Methods like strip() require parentheses to be called. Here, strip is used without parentheses, so it is a method object, not called.

2. Step 2: Understand the error

   Trying to call lower() on a method object causes an error because strip was not executed.

3. Final Answer:

   strip() is missing parentheses -> Option C

4. Quick Check:

   Method calls need () [OK]

Hint: Always add () to call methods [OK]

Common Mistakes:

• Forgetting parentheses on methods
• Thinking order of strip and lower causes error
• Assuming replace() is required

5. You have a list of product codes with inconsistent formatting:

codes = ['  AB123 ', 'cd456', ' EF789', 'GH 012 ']

Which code snippet correctly cleans all codes by removing leading and trailing spaces and converting to lowercase?

hard

A. cleaned = [code.strip().lower() for code in codes]

B. cleaned = [code.lower() for code in codes]

C. cleaned = [code.replace(' ', '').lower() for code in codes]

D. cleaned = [code.strip().replace(' ', '').lower() for code in codes]

Solution

1. Step 1: Understand the goal

   We want to remove leading and trailing whitespace from each code and convert all letters to lowercase, preserving internal spaces.

2. Step 2: Analyze each option

   cleaned = [code.strip().lower() for code in codes] uses strip() to remove leading/trailing whitespace then lower() to convert case. Correct (e.g., 'GH 012 ' -> 'gh 012').
   cleaned = [code.lower() for code in codes] only converts to lowercase, leaves leading/trailing spaces. Incorrect.
   cleaned = [code.replace(' ', '').lower() for code in codes] removes all spaces including internal ('GH 012 ' -> 'gh012'). Incorrect.
   cleaned = [code.strip().replace(' ', '').lower() for code in codes] replace() removes internal spaces after strip(). Incorrect.

3. Final Answer:

   cleaned = [code.strip().lower() for code in codes] -> Option A

4. Quick Check:

   strip then lower cleans codes [OK]

Hint: Use strip() then lower() in list comprehension [OK]

Common Mistakes:

• Forgetting strip() and only using lower() leaves spaces
• Using replace(' ', '') removes internal spaces
• Redundant replace after strip removes internal spaces