reversed() function in Python - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to reverse the list using the reversed() function.

Python

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

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

Areverse

Breversed

Csort

Dappend

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'reverse' which is a list method, not a function.

Using 'sort' which sorts the list, not reverses it.

The reversed() function returns an iterator that accesses the given sequence in the reverse order. Wrapping it with list() converts it back to a list.

2fill in blank

medium

Complete the code to print each character of the string in reverse order using reversed().

Python

word = "hello"
for char in [1](word):
    print(char, end='')

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

Asort

Breverse

Creversed

Dlist

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to use 'reverse' which is not a function.

Using 'list' which converts to list but does not reverse.

The reversed() function can be used on strings to get an iterator that yields characters in reverse order.

3fill in blank

hard

Fix the error in the code to correctly reverse the tuple using reversed().

Python

data = (10, 20, 30)
reversed_data = [1](data)
print(tuple(reversed_data))

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

Areverse

Blist

Csort

Dreversed

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'reverse' which is a list method, not available for tuples.

Using 'sort' which is not valid for tuples.

The reversed() function works on tuples and returns an iterator. The reverse() method does not exist for tuples.

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 characters.

Python

words = ['apple', 'bat', 'carrot', 'dog']
lengths = [1]: len(word) for word in words if len(word) [2] 3

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

A{word

B>

C>=

D[word

Attempts:

3 left

💡 Hint

Common Mistakes

Using square brackets instead of curly braces for dictionary.

Using '>=' instead of '>' which includes words of length 3.

The dictionary comprehension syntax requires curly braces and a colon. The condition filters words longer than 3 characters using '>'.

5fill in blank

hard

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

Python

words = ['apple', 'bat', 'carrot', 'dog']
result = [1]: [2] for word in words if len(word) [3] 3

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

A{word.upper()

Blen(word)

C>

D[word.upper()

Attempts:

3 left

💡 Hint

Common Mistakes

Using square brackets instead of curly braces for dictionary.

Not converting words to uppercase for keys.

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

The dictionary comprehension uses curly braces with uppercase words as keys and their lengths as values. The condition filters words longer than 3 characters using '>'.

Practice

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

easy

A. It sorts the items of a sequence in ascending order.

B. It returns an iterator that goes through the items of a sequence backwards.

C. It removes duplicate items from a sequence.

D. It changes the original sequence to its reversed form.

Solution

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

   The reversed() function returns an iterator that accesses the elements of a sequence in reverse order.

2. Step 2: Check if original sequence changes

   The original sequence remains unchanged; reversed() only provides a way to loop backwards.

3. Final Answer:

   It returns an iterator that goes through the items of a sequence backwards. -> Option B

4. Quick Check:

   reversed() returns reversed iterator [OK]

Hint: Remember: reversed() does not change original, just reads backwards [OK]

Common Mistakes:

• Thinking reversed() sorts the sequence
• Assuming reversed() modifies the original sequence
• Confusing reversed() with removing duplicates

2. Which of the following is the correct way to use reversed() to print characters of a string backwards?

easy

A. for ch in reversed('hello'): print(ch)

B. for ch in reverse('hello'): print(ch)

C. for ch in 'hello'.reversed(): print(ch)

D. for ch in reversed['hello']: print(ch)

Solution

1. Step 1: Identify correct function syntax

   reversed() is a built-in function called with parentheses and a sequence inside, like reversed('hello').

2. Step 2: Check loop syntax

   The for loop correctly iterates over the reversed iterator returned by reversed().

3. Final Answer:

   for ch in reversed('hello'): print(ch) -> Option A

4. Quick Check:

   Use reversed() with parentheses and a sequence [OK]

Hint: Use reversed() with parentheses, not square brackets or dot calls [OK]

Common Mistakes:

• Using square brackets instead of parentheses
• Calling reversed as a method on string
• Typing reverse instead of reversed

3. What is the output of this code?

print(list(reversed([1, 2, 3, 4])))

medium

A. Error: reversed() cannot be used on lists

B. [1, 2, 3, 4]

C. [4, 3, 2, 1]

D. [1, 4, 3, 2]

Solution

1. Step 1: Apply reversed() to the list

   reversed([1, 2, 3, 4]) returns an iterator that goes through the list backwards: 4, 3, 2, 1.

2. Step 2: Convert iterator to list

   Using list() on the reversed iterator collects all items into a new list in reversed order.

3. Final Answer:

   [4, 3, 2, 1] -> Option C

4. Quick Check:

   list(reversed([1,2,3,4])) = [4,3,2,1] [OK]

Hint: Wrap reversed() with list() to see reversed items as a list [OK]

Common Mistakes:

• Expecting reversed() to return a list directly
• Confusing reversed() with sort()
• Thinking reversed() modifies original list

4. What is wrong with this code?

my_str = 'abc'
rev_str = reversed(my_str)
print(rev_str)

medium

A. It prints a reversed iterator object, not the reversed string.

B. It prints a reversed string directly.

C. It causes a syntax error because reversed() needs a list.

D. It modifies my_str permanently.

Solution

1. Step 1: Understand what reversed() returns

   reversed(my_str) returns an iterator, not a string.

2. Step 2: Printing the iterator shows its object info

   Printing rev_str directly prints something like <reversed object at ...>, not the reversed characters.

3. Final Answer:

   It prints a reversed iterator object, not the reversed string. -> Option A

4. Quick Check:

   reversed() returns iterator, print shows object [OK]

Hint: Convert reversed() result to list or string before printing [OK]

Common Mistakes:

• Expecting reversed() to return a string
• Trying to print reversed() result directly
• Thinking reversed() modifies original string

5. How can you use reversed() to create a new string that is the reverse of the original string s = 'Python'?

hard

A. new_s = s.reverse()

B. new_s = reversed(s)

C. new_s = s[::-1]

D. new_s = ''.join(reversed(s))

Solution

1. Step 1: Use reversed() to get reversed iterator

   reversed(s) returns an iterator over characters of s in reverse order.

2. Step 2: Join characters into a new string

   ''.join(reversed(s)) combines the reversed characters into a new string.

3. Final Answer:

   new_s = ''.join(reversed(s)) -> Option D

4. Quick Check:

   Use join() with reversed() to build reversed string [OK]

Hint: Use ''.join(reversed(s)) to reverse strings easily [OK]

Common Mistakes:

• Assigning reversed(s) directly to string variable
• Using s.reverse() which is invalid for strings
• Confusing slicing with reversed()