#!/usr/bin/env python

workers = [
    {
        'name': 'Piotr',
        'surname': 'Kowalski',
        'city': 'Warszawa',
    }, 
    {
        'name': 'Julian',
        'surname': 'Wysoki',
        'city': 'Krakow',
    },
    {
        'name': 'Andrzej',
        'surname': 'Niski',
        'city': 'Warszawa',
    },
]

unique_cities = None

# unique_cities = ...

print(unique_cities)
