Membership operators (in, not in) in Python - Mini Project: Build & Apply

Using Membership Operators (in, not in) in Python

📖 Scenario: You work at a library. You have a list of books currently available on the shelves. You want to check if certain books are in the library or not.

🎯 Goal: Build a small program that checks if some books are available in the library using membership operators in and not in.

📋 What You'll Learn

Create a list called library_books with exact book titles

Create a variable called check_book with a specific book title

Use in or not in to check if check_book is in library_books

Print the result as a sentence

💡 Why This Matters

🌍 Real World

Libraries, stores, and many apps need to check if an item is available in a collection before proceeding.

💼 Career

Understanding membership operators helps in filtering data, validating inputs, and controlling program flow in many programming jobs.

1

Create the list of books

Create a list called library_books with these exact book titles: 'The Hobbit', '1984', 'Pride and Prejudice', 'To Kill a Mockingbird', and 'The Great Gatsby'.

Python

# Create the list library_books with the given book titles
# Your code here

Hint

Remember to use square brackets [] to create a list and separate items with commas.

2

Set the book to check

Create a variable called check_book and set it to the string '1984'.

Python

library_books = ['The Hobbit', '1984', 'Pride and Prejudice', 'To Kill a Mockingbird', 'The Great Gatsby']
# Create the variable check_book and set it to '1984'
# Your code here

Hint

Use simple assignment with the exact string '1984'.

3

Check if the book is in the library

Use an if statement with the membership operator in to check if check_book is in library_books. Inside the if, create a variable called message and set it to "The book is available in the library.". In the else part, set message to "The book is not available in the library.".

Python

library_books = ['The Hobbit', '1984', 'Pride and Prejudice', 'To Kill a Mockingbird', 'The Great Gatsby']
check_book = '1984'
# Use if with 'in' to check if check_book is in library_books
# Set message accordingly
# Your code here

Hint

Use if check_book in library_books: to check membership.

4

Print the result message

Print the variable message to show if the book is available or not.

Python

library_books = ['The Hobbit', '1984', 'Pride and Prejudice', 'To Kill a Mockingbird', 'The Great Gatsby']
check_book = '1984'
if check_book in library_books:
    message = "The book is available in the library."
else:
    message = "The book is not available in the library."
# Print the message
# Your code here

Hint

Use print(message) to show the result.

Practice

1. What does the in operator do in Python?

easy

A. Creates a new collection

B. Adds a value to a collection

C. Removes a value from a collection

D. Checks if a value exists inside a collection

Solution

1. Step 1: Understand the purpose of in

   The in operator is used to check if a value is present inside a collection like a list, string, or tuple.

2. Step 2: Compare with other options

   Options A, B, and C describe actions unrelated to membership checking.

3. Final Answer:

   Checks if a value exists inside a collection -> Option D

4. Quick Check:

   in means membership check [OK]

Hint: Remember: in means 'is inside' [OK]

Common Mistakes:

• Confusing in with adding or removing items
• Thinking in changes the collection
• Mixing in with comparison operators

2. Which of the following is the correct syntax to check if the string 'apple' is NOT in the list fruits?

easy

A. if 'apple' not in fruits:

B. if 'apple' not fruits:

C. if not 'apple' fruits:

D. if 'apple' !in fruits:

Solution

1. Step 1: Recall correct syntax for not in

   The correct syntax to check absence is value not in collection.

2. Step 2: Evaluate each option

   if 'apple' not in fruits: matches correct syntax. if 'apple' not fruits: misses in. if not 'apple' fruits: misses in. if 'apple' !in fruits: uses invalid operator !in.

3. Final Answer:

   if 'apple' not in fruits: -> Option A

4. Quick Check:

   Use not in as two words [OK]

Hint: Use not in as two words, no symbols [OK]

Common Mistakes:

• Writing !in instead of not in
• Omitting in after not
• Using not 'value' in which is valid but less clear

3. What is the output of this code?

letters = ['a', 'b', 'c']
print('d' in letters)
print('a' not in letters)

medium

A. True\nTrue

B. False\nTrue

C. False\nFalse

D. True\nFalse

Solution

1. Step 1: Check if 'd' is in the list

   'd' is not in ['a', 'b', 'c'], so 'd' in letters is False.

2. Step 2: Check if 'a' is not in the list

   'a' is in the list, so 'a' not in letters is False, so print('a' not in letters) prints False.

3. Final Answer:

   False False is incorrect because the second print outputs False, but the first print outputs False, so the correct output is False False which matches False\nFalse.

4. Quick Check:

   'd' in letters = False, 'a' not in letters = False [OK]

Hint: Check each membership separately [OK]

Common Mistakes:

• Assuming 'd' is in the list
• Mixing up in and not in results
• Confusing True/False outputs

4. Find the error in this code snippet:

items = ['pen', 'pencil', 'eraser']
if 'pen' not items:
    print('Pen is missing')

medium

A. Incorrect print statement syntax

B. Wrong list name

C. Missing in after not

D. No error, code is correct

Solution

1. Step 1: Check the membership syntax

   The correct syntax for checking absence is value not in collection. The code misses in after not.

2. Step 2: Verify other parts

   List name and print statement are correct. The only error is missing in.

3. Final Answer:

   Missing in after not -> Option C

4. Quick Check:

   Use not in together [OK]

Hint: Always write not in together [OK]

Common Mistakes:

• Writing not items instead of not in items
• Forgetting in keyword
• Assuming not alone checks membership

5. You have a list words = ['cat', 'dog', 'bird']. You want to print all words that are NOT in the string text = 'I have a dog and a cat'. Which code correctly does this?

hard

A. for w in words:
if w not in text:
print(w)

B. for w in words:
if w in text:
print(w)

C. for w in words:
if not w text:
print(w)

D. for w in words:
if w not text:
print(w)

Solution

1. Step 1: Understand the goal

   We want to print words from the list that are NOT found inside the string text.

2. Step 2: Check each option's logic

   for w in words: if w not in text: print(w) uses if w not in text, which correctly checks absence. for w in words: if w in text: print(w) prints words that ARE in text, opposite of goal. for w in words: if not w text: print(w) has syntax error, missing in after w. for w in words: if w not text: print(w) has syntax error missing in.

3. Final Answer:

   for w in words: if w not in text: print(w) -> Option A

4. Quick Check:

   Use not in for absence check [OK]

Hint: Use if w not in text to find missing words [OK]

Common Mistakes:

• Omitting in keyword in various positions
• Forgetting in keyword
• Printing words that are present instead of absent