Why built-in functions are useful in Python - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to use a built-in function that finds the length of a list.

Python

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

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

Alen

Bcount

Csize

Dlength

Attempts:

3 left

💡 Hint

Common Mistakes

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

Trying to use 'count' which counts occurrences of a value, not list length.

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

2fill in blank

medium

Complete the code to convert a string to uppercase using a built-in function.

Python

word = "hello"
upper_word = word.[1]()
print(upper_word)

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

Atitle

Bcapitalize

Clower

Dupper

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'lower' which makes letters small.

Using 'capitalize' which only changes the first letter.

The upper() method converts all letters in a string to uppercase.

3fill in blank

hard

Fix the error by completing the code to find the maximum number in a list using a built-in function.

Python

values = [10, 20, 30, 40]
max_value = [1](values)
print(max_value)

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

Amaxnum

Bmax

Cmax_value

Dmaximum

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'maximum' which is not a built-in function.

Trying to use variable names as functions.

The built-in function max() returns the largest item in a list.

4fill in blank

hard

Fill both blanks to create a dictionary with word lengths only for words longer than 3 letters.

Python

words = ['cat', 'elephant', 'dog', 'giraffe']
lengths = {word: [1] for word in words if len(word) [2] 3}
print(lengths)

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

Alen(word)

B>

C<

Dword

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>' which selects shorter words.

Putting 'word' instead of 'len(word)' for the dictionary values.

Use len(word) to get the length and > to filter words longer than 3 letters.

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 4 letters.

Python

words = ['apple', 'bat', 'carrot', 'dog']
result = { [1]: [2] for w in words if len(w) [3] 4 }
print(result)

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

Aw.upper()

Blen(w)

C>

Dw.lower()

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'w.lower()' instead of uppercase for keys.

Using '<' instead of '>' for filtering.

Putting 'w' instead of 'len(w)' for values.

Use w.upper() for keys, len(w) for values, and > to filter words longer than 4 letters.

Practice

1. Why are built-in functions useful in Python?

easy

A. They make the code run slower

B. They are only for advanced users

C. They require writing more code

D. They save time by doing common tasks quickly

Solution

1. Step 1: Understand the purpose of built-in functions

   Built-in functions are ready-made tools in Python that perform common tasks efficiently.

2. Step 2: Identify the benefit of using them

   Using built-in functions saves time and reduces the chance of errors compared to writing code from scratch.

3. Final Answer:

   They save time by doing common tasks quickly -> Option D

4. Quick Check:

   Built-in functions = Save time [OK]

Hint: Built-in functions speed up coding and reduce mistakes [OK]

Common Mistakes:

• Thinking built-in functions slow down code
• Believing built-in functions require more code
• Assuming only experts use built-in functions

2. Which of the following is the correct way to use the built-in len() function to get the length of a list my_list?

easy

A. length = length(my_list)

B. length = my_list.len()

C. length = len(my_list)

D. length = len:my_list

Solution

1. Step 1: Recall the syntax of the len() function

   The built-in function len() takes the object inside parentheses to return its length.

2. Step 2: Check each option's syntax

   length = len(my_list) uses len(my_list) which is correct. The other options use incorrect syntax.

3. Final Answer:

   length = len(my_list) -> Option C

4. Quick Check:

   len() syntax = len(object) [OK]

Hint: Remember: function_name(arguments) with parentheses [OK]

Common Mistakes:

• Using dot notation like my_list.len()
• Writing function name without parentheses
• Using colon instead of parentheses

3. What is the output of this code?

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

medium

A. 10

B. [1, 2, 3, 4]

C. 1234

D. Error

Solution

1. Step 1: Understand what sum() does

   The built-in function sum() adds all numbers in an iterable like a list.

2. Step 2: Calculate the sum of the list elements

   Adding 1 + 2 + 3 + 4 equals 10.

3. Final Answer:

   10 -> Option A

4. Quick Check:

   sum([1,2,3,4]) = 10 [OK]

Hint: sum() adds numbers inside a list or tuple [OK]

Common Mistakes:

• Printing the list instead of sum
• Concatenating numbers as strings
• Expecting sum() to return an error

4. The code below tries to find the maximum number in a list but causes an error. What is the problem?

nums = [5, 3, 9, 1]
max_num = max nums
print(max_num)

medium

A. Missing parentheses after max function

B. max() cannot be used on lists

C. Variable name max_num is invalid

D. List nums is empty

Solution

1. Step 1: Check the syntax of max() usage

   The built-in function max() requires parentheses around its argument.

2. Step 2: Identify the error in the code

   The code writes max nums without parentheses, causing a syntax error.

3. Final Answer:

   Missing parentheses after max function -> Option A

4. Quick Check:

   Function call needs parentheses [OK]

Hint: Always use parentheses when calling functions [OK]

Common Mistakes:

• Forgetting parentheses on function calls
• Thinking max() can't handle lists
• Assuming variable names cause errors

5. You want to create a dictionary that maps each word in a list words = ['apple', 'banana', 'cherry'] to its length using a built-in function. Which code correctly does this?

hard

A. word_lengths = [word: len(word) for word in words]

B. word_lengths = {word: len(word) for word in words}

C. word_lengths = {len(word): word for word in words}

D. word_lengths = dict(len(word) for word in words)

Solution

1. Step 1: Understand dictionary comprehension syntax

   Dictionary comprehension uses curly braces with key:value pairs for each item.

2. Step 2: Check which option correctly maps words to their lengths

   word_lengths = {word: len(word) for word in words} uses {word: len(word) for word in words}, which correctly creates the dictionary.

3. Final Answer:

   word_lengths = {word: len(word) for word in words} -> Option B

4. Quick Check:

   Dict comprehension with len() = word_lengths = {word: len(word) for word in words} [OK]

Hint: Use {key: value for item in list} for dict comprehension [OK]

Common Mistakes:

• Using list brackets [] instead of curly braces {}
• Swapping key and value positions
• Trying to use dict() with a generator incorrectly