reversed() function in Python - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the reversed() function do in Python?

It returns an iterator that accesses the given sequence in reverse order without changing the original sequence.

beginner

Can reversed() be used on any iterable in Python?

No, reversed() works only on sequences that support indexing and have a defined length, like lists, tuples, and strings.

beginner

How do you convert the result of reversed() into a list?

Use the list() function around reversed(), like list(reversed(my_list)).

beginner

What is the output of list(reversed('hello'))?

['o', 'l', 'l', 'e', 'h'] - the characters of the string 'hello' in reverse order as a list.

beginner

Does reversed() modify the original sequence?

No, it does not change the original sequence; it only provides a reversed iterator.

Which of these can reversed() be used on?

A A dictionary

B A list

C A set

D A generator

reversed() works on sequences like lists, not on dictionaries, sets, or generators.

What type does reversed() return?

A A list

B A string

C A tuple

D An iterator

reversed() returns an iterator that you can loop over or convert to a list.

How do you get a reversed list from a tuple t?

A list(reversed(t))

B reversed(list(t))

C t[::-1]

D All of the above

Only list(reversed(t)) produces a reversed list from a tuple t. reversed(list(t)) returns an iterator and t[::-1] returns a reversed tuple.

What happens if you try reversed() on a set?

A It returns a reversed iterator

B It returns the set unchanged

C It raises a TypeError

D It converts the set to a list automatically

reversed() requires a sequence with indexing; sets do not support this, so it raises an error.

Which of these is a correct way to print characters of a string in reverse?

A Both B and C

B print('abc'[::-1])

C print(list(reversed('abc')))

D print(reversed('abc'))

Slicing with [::-1] and converting reversed() to list both print reversed characters.

Explain how the reversed() function works and when you would use it.

Think about how you might want to read a list or string backwards without changing it.

Describe the difference between using reversed() and slicing with [::-1] to reverse a sequence.

Consider the type of result and performance differences.