len() function in Python - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to find the length of the list.

Python

my_list = [1, 2, 3, 4]
length = [1](my_list)
print(length)

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

Acount

Bsize

Clen

Dlength

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'size' or 'count' instead of 'len()'.

Trying to access a property like 'length' instead of calling a function.

The len() function returns the number of items in a list.

2fill in blank

medium

Complete the code to get the length of the string.

Python

word = "hello"
word_length = [1](word)
print(word_length)

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

Alen

Bcount

Csize

Dlength

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'count' which is a string method but requires an argument.

Using 'size' or 'length' which are not functions in Python.

The len() function works for strings to count characters.

3fill in blank

hard

Fix the error in the code to correctly get the length of the tuple.

Python

my_tuple = (1, 2, 3)
length = [1](my_tuple)
print(length)

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

Asize

Blength

Ccount

Dlen

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'size' or 'length' which are not Python functions.

Trying to use 'count' which is a method but needs an argument.

The len() function works for tuples to count elements.

4fill in blank

hard

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

Python

words = ["apple", "bat", "car", "door"]
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 itself as the value instead of its length.

The dictionary comprehension uses the word as the key and its length as the value.

5fill in blank

hard

Fill all three blanks to create a dictionary with uppercase words as keys and their lengths as values for words longer than 3 letters.

Python

words = ["tree", "sun", "flower", "sky"]
lengths = { [1]: [2] for word in words if len(word) [3] 3 }

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

Aword.upper()

Blen(word)

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>' in the condition.

Using the original word instead of uppercase for keys.

The dictionary comprehension uses the uppercase word as the key, the length as the value, and filters words longer than 3 letters.

Practice

1. What does the len() function do in Python?

easy

A. It returns the number of items in an object like a string or list.

B. It adds two numbers together.

C. It prints text to the screen.

D. It creates a new list.

Solution

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

   The len() function counts how many items are inside an object like a string, list, or dictionary.

2. Step 2: Compare options with the function's purpose

   Only It returns the number of items in an object like a string or list. correctly describes this behavior. Other options describe different actions.

3. Final Answer:

   It returns the number of items in an object like a string or list. -> Option A

4. Quick Check:

   len() counts items [OK]

Hint: Remember: len() counts items inside, not math or printing [OK]

Common Mistakes:

• Thinking len() adds numbers
• Confusing len() with print()
• Believing len() creates new lists

2. Which of the following is the correct way to use len() to find the length of a list named fruits?

easy

A. length = fruits.len()

B. length = len[fruits]

C. length = len(fruits)

D. length = len.fruits()

Solution

1. Step 1: Recall correct syntax for calling functions

   Functions in Python use parentheses with the object inside, like len(fruits).

2. Step 2: Check each option's syntax

   length = len(fruits) uses correct syntax. Options B, C, and D misuse brackets, dot notation, or parentheses.

3. Final Answer:

   length = len(fruits) -> Option C

4. Quick Check:

   Use parentheses with len() [OK]

Hint: Use parentheses with len(), not brackets or dots [OK]

Common Mistakes:

• Using square brackets instead of parentheses
• Trying to call len() as a method on the object
• Using dot notation incorrectly

3. What will be the output of this code?

my_list = [10, 20, 30, 40]
print(len(my_list))

medium

A. 3

B. Error

C. 40

D. 4

Solution

1. Step 1: Identify the list elements

   The list my_list contains 4 items: 10, 20, 30, and 40.

2. Step 2: Apply len() to the list

   The len() function returns the number of items, which is 4.

3. Final Answer:

   4 -> Option D

4. Quick Check:

   len([10,20,30,40]) = 4 [OK]

Hint: Count items inside the list to find len() [OK]

Common Mistakes:

• Confusing last item value with length
• Off-by-one counting errors
• Expecting len() to return sum

4. The following code gives an error. What is the problem?

my_string = "hello"
print(len my_string)

medium

A. Missing parentheses after len

B. Using double quotes instead of single quotes

C. Variable name is invalid

D. len() cannot be used on strings

Solution

1. Step 1: Check the syntax of the len() function call

   Functions require parentheses around their arguments. Here, len is called without parentheses.

2. Step 2: Identify the error cause

   Missing parentheses cause a syntax error. Other options are incorrect because double quotes are allowed, variable name is valid, and len() works on strings.

3. Final Answer:

   Missing parentheses after len -> Option A

4. Quick Check:

   Always use parentheses with len() [OK]

Hint: Always put parentheses after len() [OK]

Common Mistakes:

• Forgetting parentheses after function name
• Thinking quotes affect len() usage
• Assuming len() can't handle strings

5. You have a dictionary data = {'a': 1, 'b': 2, 'c': 3}. You want to check if it has exactly 3 keys before processing. Which code correctly uses len() for this check?

hard

A. if len(data.values()) < 3:
print("Correct number of keys")

B. if len(data) == 3:
print("Correct number of keys")

C. if len(data.keys()) > 3:
print("Correct number of keys")

D. if len(data.items()) != 3:
print("Correct number of keys")

Solution

1. Step 1: Understand what len() returns for a dictionary

   Using len() on a dictionary returns the number of keys.

2. Step 2: Check the condition for exactly 3 keys

   if len(data) == 3: print("Correct number of keys") checks if len(data) equals 3, which is correct. Other options check for greater than, less than, or not equal, which do not match the requirement.

3. Final Answer:

   if len(data) == 3: print("Correct number of keys") -> Option B

4. Quick Check:

   len(dict) counts keys [OK]

Hint: len(dict) gives number of keys directly [OK]

Common Mistakes:

• Using > or < instead of == for exact count
• Checking values or items unnecessarily
• Misunderstanding what len(dict) returns