"""Sets.

@see: https://www.w3schools.com/python/python_sets.asp
@see: https://docs.python.org/3.7/tutorial/datastructures.html#sets

A set is a collection which is unordered and unindexed.
In Python sets are written with curly brackets.

Set objects also support mathematical operations like union, intersection, difference, and
symmetric difference.
"""


def test_sets():
    """Sets"""
    fruits_set = {"apple", "banana", "cherry"}

    assert isinstance(fruits_set, set)

    # It is also possible to use the set() constructor to make a set.
    # Note the double round-brackets
    fruits_set_via_constructor = set(("apple", "banana", "cherry"))

    assert isinstance(fruits_set_via_constructor, set)


def test_set_methods():
    """Set methods"""

    fruits_set = {"apple", "banana", "cherry"}

    # You may check if the item is in set by using "in" statement
    assert "apple" in fruits_set
    assert "pineapple" not in fruits_set

    # Use the len() method to return the number of items.
    assert len(fruits_set) == 3

    # You can use the add() object method to add an item.
    fruits_set.add("pineapple")
    assert "pineapple" in fruits_set
    assert len(fruits_set) == 4

    # Use remove() method to remove an item.
    fruits_set.remove("pineapple")
    assert "pineapple" not in fruits_set
    assert len(fruits_set) == 3

    # Demonstrate set operations on unique letters from two word:
    first_char_set = set('abracadabra')
    second_char_set = set('alacazam')

    assert first_char_set == {'a', 'r', 'b', 'c', 'd'}  # unique letters in first word
    assert second_char_set == {'a', 'l', 'c', 'z', 'm'}  # unique letters in second word

    # Letters in first word but not in second.
    assert first_char_set - second_char_set == {'r', 'b', 'd'}

    # Letters in first word or second word or both.
    assert first_char_set | second_char_set == {'a', 'c', 'r', 'd', 'b', 'm', 'z', 'l'}

    # Common letters in both words.
    assert first_char_set & second_char_set == {'a', 'c'}

    # Letters in first or second word but not both.
    assert first_char_set ^ second_char_set == {'r', 'd', 'b', 'm', 'z', 'l'}

    # Similarly to list comprehensions, set comprehensions are also supported:
    word = {char for char in 'abracadabra' if char not in 'abc'}
    assert word == {'r', 'd'}