List length and membership test in Python - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to print the length of the list.

Python

numbers = [1, 2, 3, 4, 5]
print(len([1]))

Drag options to blanks, or click blank then click option'

Alist

Bnumbers

Clen

D5

Attempts:

3 left

💡 Hint

Common Mistakes

Putting the number 5 inside len() instead of the list variable.

Using the word 'list' instead of the list variable name.

The len() function returns the number of items in a list. Here, we want the length of the numbers list.

2fill in blank

medium

Complete the code to check if the number 3 is in the list.

Python

fruits = ['apple', 'banana', 'cherry']
if [1] in fruits:
    print('Found it!')

Drag options to blanks, or click blank then click option'

A'3'

B'banana'

C3

D'cherry'

Attempts:

3 left

💡 Hint

Common Mistakes

Checking for the number 3 instead of a fruit name.

Using quotes incorrectly or missing quotes around the string.

We check if the string 'cherry' is in the list fruits. The in keyword tests membership.

3fill in blank

hard

Fix the error in the code to correctly check if 'cat' is in the list.

Python

animals = ['dog', 'cat', 'bird']
if 'cat' [1] animals:
    print('Cat found!')

Drag options to blanks, or click blank then click option'

Ain

Bnot in

Cis in

Dcontains

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'is in' or 'contains' which cause syntax errors.

Using 'not in' which checks the opposite condition.

The correct keyword to check membership is in. The phrase is in or contains are not valid Python syntax.

4fill in blank

hard

Fill both blanks to create a dictionary with words as keys and their lengths as values, but only for words longer than 3 letters.

Python

words = ['sun', 'moon', 'star', 'sky']
lengths = { [1] : [2] for word in words if len(word) > 3 }

Drag options to blanks, or click blank then click option'

Aword

Blen(word)

Cword.upper()

Dword.lower()

Attempts:

3 left

💡 Hint

Common Mistakes

Using word.upper() or word.lower() as keys instead of the original word.

Using the word variable as value instead of its length.

The dictionary comprehension uses each word as the key and its length len(word) as the value. The condition filters words longer than 3 letters.

5fill in blank

hard

Fill all three blanks to create a dictionary with uppercase words as keys, their lengths as values, but only include words with length greater than 3.

Python

words = ['tree', 'sky', 'river', 'sun']
result = { [1] : [2] for [3] in words if len([3]) > 3 }

Drag options to blanks, or click blank then click option'

Aword.upper()

Blen(word)

Cword

Ditem

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names inconsistently.

Not converting words to uppercase for keys.

Using the wrong variable in the condition.

The dictionary comprehension uses word.upper() as keys, len(word) as values, and iterates over word in the list. The condition filters words longer than 3 letters.

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