Yet another example of type safety in Python

Python can be safe (if we need it) too. Another example is: let's say we want to implement a function unique(). It may looks like:

def unique(data):
    res: list = []
    for x in data:
        if res and x == res[-1]: continue
        else: res.append(x)
    return res

Truth is that data should be sorted - we don't want to sort it because data items maybe are sorted already. So, instead to write docstring about this our requirement ("data should be sorted") we can specify this requirement as a type, so it will prevent a client from passing of data which was not sorted, so the check will work at compile time:

from typing import *

class Sorted(list):
    def __init__(self, items):
        super().__init__(sorted(items))

def unique(data: Sorted) -> list:
    res: list = []
    for x in data:
        if res and x == res[-1]: continue
        else: res.append(x)
    return res

items = 11, 20, 11, 20, 1, 20, 11, 5, 1
data = Sorted(items)
print(unique(items))

And if we try to pass something which has not type Sorted then we will get an MYPY error at compile time. It looks like Haskell, ah? :)