List length and membership test in Python - Mini Project: Build & Apply

List length and membership test

📖 Scenario: You are organizing a small party and have a list of guests who have confirmed their attendance.You want to check how many guests are coming and whether a special friend is on the list.

🎯 Goal: Create a list of guests, count how many guests are coming, check if a special friend is attending, and print the results.

📋 What You'll Learn

Create a list called guests with the exact names: 'Alice', 'Bob', 'Charlie', 'Diana'

Create a variable called special_friend and set it to 'Charlie'

Create a variable called guest_count that stores the length of the guests list

Create a variable called is_special_friend_coming that checks if special_friend is in the guests list

Print the number of guests and whether the special friend is coming exactly as shown

💡 Why This Matters

🌍 Real World

Managing guest lists for events or parties is a common task. Knowing how to count attendees and check if important people are coming helps with planning.

💼 Career

This teaches basic list handling and condition checking, foundational skills for data processing, user management, and many programming jobs.

1

Create the guest list

Create a list called guests with these exact names: 'Alice', 'Bob', 'Charlie', 'Diana'

Python

# Create the guests list with the exact names
# Your code here

Hint

Use square brackets [] to create a list and separate names with commas.

2

Set the special friend

Create a variable called special_friend and set it to the string 'Charlie'

Python

guests = ['Alice', 'Bob', 'Charlie', 'Diana']
# Create the special_friend variable
# Your code here

Hint

Use an equals sign = to assign the string 'Charlie' to special_friend.

3

Count guests and check membership

Create a variable called guest_count that stores the length of the guests list using the len() function. Then create a variable called is_special_friend_coming that checks if special_friend is in the guests list using the in keyword.

Python

guests = ['Alice', 'Bob', 'Charlie', 'Diana']
special_friend = 'Charlie'
# Create guest_count using len(guests)
# Create is_special_friend_coming using 'in' keyword
# Your code here

Hint

Use len(guests) to get the number of guests. Use special_friend in guests to check if the friend is coming.

4

Print the results

Print the number of guests using print(f"Number of guests: {guest_count}") and print whether the special friend is coming using print(f"Is special friend coming? {is_special_friend_coming}")

Python

guests = ['Alice', 'Bob', 'Charlie', 'Diana']
special_friend = 'Charlie'
guest_count = len(guests)
is_special_friend_coming = special_friend in guests
# Print the number of guests
# Print if the special friend is coming
# Your code here

Hint

Use print() with f-strings to show the results clearly.

Practice

1.

What does the len() function do when used with a list in Python?

easy

A. It removes the last item from the list.

B. It checks if an item is in the list.

C. It adds a new item to the list.

D. It returns the number of items in the list.

Solution

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

   The len() function counts how many elements are inside a list.

2. Step 2: Compare with other options

   Checking membership uses in, adding uses append(), removing uses pop().

3. Final Answer:

   It returns the number of items in the list. -> Option D

4. Quick Check:

   len() counts items [OK]

Hint: Remember: len() counts items, in checks presence [OK]

Common Mistakes:

• Confusing len() with in operator
• Thinking len() adds or removes items
• Mixing up list methods with functions

2.

Which of the following is the correct syntax to check if the number 5 is in the list nums?

nums = [1, 3, 5, 7]

easy

A. if 5 inside nums:

B. if nums in 5:

C. if 5 in nums:

D. if nums contains 5:

Solution

1. Step 1: Recall correct membership syntax

   Python uses in to check if an item is inside a list: item in list.

2. Step 2: Check each option

   Only if 5 in nums: matches correct syntax; others are invalid Python.

3. Final Answer:

   if 5 in nums: -> Option C

4. Quick Check:

   Use in for membership test [OK]

Hint: Use 'item in list' to check membership [OK]

Common Mistakes:

• Writing 'inside' or 'contains' instead of 'in'
• Reversing order like 'list in item'
• Using invalid keywords for membership

3.

What will be the output of this code?

fruits = ['apple', 'banana', 'cherry']
print(len(fruits))
print('banana' in fruits)
print('orange' in fruits)

medium

A. 3\nTrue\nFalse

B. 3\nFalse\nTrue

C. Error\nTrue\nFalse

D. 3\nTrue\nTrue

Solution

1. Step 1: Calculate length of the list

   The list has 3 items: 'apple', 'banana', 'cherry', so len(fruits) is 3.

2. Step 2: Check membership for 'banana' and 'orange'

   'banana' is in the list, so 'banana' in fruits is True. 'orange' is not, so 'orange' in fruits is False.

3. Final Answer:

   3 True False -> Option A

4. Quick Check:

   len=3, banana in list=True, orange in list=False [OK]

Hint: Count items with len(), check presence with in [OK]

Common Mistakes:

• Confusing True/False for membership
• Miscounting list length
• Expecting syntax error for correct code

4.

Find the error in this code snippet:

items = [10, 20, 30]
if 20 in items
    print("Found 20")

medium

A. Missing colon ':' after the if condition.

B. Wrong use of 'in' operator.

C. List should be defined with parentheses, not brackets.

D. print statement syntax is incorrect.

Solution

1. Step 1: Check syntax of if statement

   Python requires a colon ':' at the end of the if condition line.

2. Step 2: Identify the missing colon

   The code has if 20 in items without a colon, causing a syntax error.

3. Final Answer:

   Missing colon ':' after the if condition. -> Option A

4. Quick Check:

   if statements need ':' [OK]

Hint: Always put ':' after if condition [OK]

Common Mistakes:

• Forgetting colon after if condition
• Misusing 'in' operator syntax
• Using parentheses instead of brackets for lists

5.

You have a list numbers = [2, 4, 6, 8]. You want to check if the list has exactly 4 items and if the number 5 is not in the list. Which code correctly does this?

hard

A. if len(numbers) = 4 and 5 not in numbers:
print("Condition met")

B. if len(numbers) == 4 and 5 not in numbers:
print("Condition met")

C. if len(numbers) == 4 or 5 in numbers:
print("Condition met")

D. if len(numbers) == 4 and 5 in numbers:
print("Condition met")

Solution

1. Step 1: Check list length condition

   Use len(numbers) == 4 to test if list has exactly 4 items.

2. Step 2: Check membership condition

   Use 5 not in numbers to confirm 5 is not in the list.

3. Step 3: Combine conditions correctly

   Use and to require both conditions true together.

4. Final Answer:

   if len(numbers) == 4 and 5 not in numbers: print("Condition met") -> Option B

5. Quick Check:

   Length check and membership negation combined with and [OK]

Hint: Use 'len() == number' and 'item not in list' with and [OK]

Common Mistakes:

• Using single '=' instead of '==' for comparison
• Using or instead of and for both conditions
• Checking for 5 in list instead of not in