PCAP String slicing Practice Question

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

• ✗

  result = s.reversed()

  Why it's wrong here

  Strings do not have a `.reversed()` method; the only `reversed` available is the built-in function `reversed()`, which must be called as `reversed(s)`, not `s.reversed()`. Attempting `s.reversed()` raises an `AttributeError` because the `str` class has no such attribute. Furthermore, even the correct built-in `reversed(s)` returns an iterator, not a string, so additional processing like `''.join()` is required to obtain the reversed string—this option confuses a method call with a built-in function.

• ✓

  result = s[::-1]

  Why this is correct

  Using extended slice syntax with a step of `-1` creates a reversed copy of the entire string: `s[::-1]` means start at the end, go to the beginning, and step backward by one. This is the most idiomatic and concise way to reverse a string in Python, and it is often preferred for its readability and speed. Since strings are immutable, this operation allocates a new string object containing the characters in reverse order, leaving the original string unchanged.

• ✗

  s.reverse()

  Why it's wrong here

  Calling `.reverse()` on a string raises an `AttributeError` because strings are immutable sequence types and do not expose this method. The `.reverse()` method is defined only on mutable list objects, where it reverses the list in place and returns `None`, meaning it cannot produce a new reversed string. Even if strings had such a method, it could not modify the original object, so this option is fundamentally incompatible with string semantics.

• ✓

  result = ''.join(reversed(s))

  Why this is correct

  This is correct: `reversed(s)` is a built-in function that returns a reverse iterator over the characters of `s`, and `''.join()` consumes that iterator, concatenating each character with an empty separator to form a new string. This approach works for any finite sequence, not just strings, and it is memory-efficient because the iterator yields characters lazily rather than constructing an intermediate list. The resulting expression is explicit and clear, making it a reliable way to reverse a string.