Concepts of `reverse-string`

Example implementation:

From the current example.py:

def reverse(text: str = "") -> str:
    """Reverse a given string"""
    return text[::-1]

[Function][function]: def to create a function in Python
[Immutability][immutability]: text str in Python is immutable. In this exercise, you return a new string, the old string text is not changed.
[Return Value][return-value]: this function return a string by this line: return text[::-1]
[Slicing][slicing]: because str in Python is a sequence type, slicing syntax can be used here. Specifically: for syntax string[start:stop:stride]:
- start: 0-index of the start position, start=0 by default (i.e., not specified) (start from the beginning)
- stop: 0-index of the stop position, stop=-1 by default (i.e., not specified) (stop at the end)
- stride: number of skip step. For example,
```
>>> string = 'ABCDEF'[::2]
>>> print(string)
'ACE'
```
- In this exercise, stride = -1 means start from the end Together effectively, slicing of [::-1] gives the reversed string Extra material for string slicing.
[Docstrings][docstrings]: used to document the function, normally situated right below def func():
[Type hinting][type-hinting]: In modern Python it's possibly to type hint annotations to parameters and variables, see typing. While not necessary in Python such annotations can help your code be easier to read, understand, and check automatically using tools like mypy.