multilang-python.md

Exercise: Reverse a String (Python)

::: exercise id: py-reverse-string difficulty: beginner time: 10 minutes :::

Write a function reverse_str that returns the reverse of a string.

::: starter file="reverse.py" language=python

def reverse_str(s: str) -> str:
    # TODO: return the reverse of s
    # Hint: try slicing or reversed()
    raise NotImplementedError

:::

::: hint level=1 title="Slicing" Python slicing supports negative steps. For example: s[::-1]. :::

::: hint level=2 title="Built-in reversed" ''.join(reversed(s)) returns a reversed string. :::

::: solution reveal=on-demand

def reverse_str(s: str) -> str:
    return s[::-1]

:::

::: tests mode=local language=python

import unittest

class TestReverse(unittest.TestCase):
    def test_reverse(self):
        self.assertEqual(reverse_str("abc"), "cba")
        self.assertEqual(reverse_str(""), "")
        self.assertEqual(reverse_str("a"), "a")

if __name__ == '__main__':
    unittest.main()

:::

::: reflection

• Which approach do you prefer: slicing or reversed()?
• How would you handle non-ASCII strings? (Hint: Python str is Unicode.) :::