This is another data type used to store values as a collection in Python. Sets offer a very interesting feature, though: uniqueness of elements. This means that if you add the same element twice (or more) to a set, it will be ignored! This is useful if you want to ensure your collection does not contain any duplicated elements:
group_1 = {"jim", "michael", "michael", "jan"} # Notice that "michael" was added twice
group_1.add("pam") # This is how you can add new elements
group_2 = set(["jim", "ryan", "kelly", "ryan"]) # It can be created this way too. Also, notice that "ryan" was added twice
print(group_1) # => {'pam', 'jan', 'jim', 'michael'}
print(group_2) # => {'ryan', 'kelly', 'jim'}
Notice that group_1 and group_2 don't contain any repeated elements, even though I tried to add duplicates into them.
Also, notice that when I print() them, the order of the elements is not respected! This has to do with some internal specifications on how Python stores these values in memory (it uses hash tables). As a consequence of that, you cannot access individual elements by index in a set, as we do in lists and tuples! As a workaround to this limitation, you can easily create a list out of a set:
group_1 = list({"jim", "michael", "michael", "jan", "pam"}) # A list created out of a set. the second "michael" will be ignored
print(group_1) # => ['jan', 'jim', 'pam', 'michael']
This procedure of converting a type into another (in this case, a set into a list), is known as “casting”.
Apart from this validation for uniqueness, another interesting use case for sets is performing union and intersection operations of elements in different sets.
group_1 = {"jim", "michael", "michael", "jan", "pam"}
group_2 = {"jim", "ryan", "kelly", "ryan"}
group_difference = group_1.difference(group_2)
print(group_difference) # => {'michael', 'pam', 'jan'}
group_union = group_1.union(group_2)
print(group_union) # => {'jim', 'pam', 'jan', 'ryan', 'kelly', 'michael'}
easier_union = group_1 | group_2 # The same as the one above
print(easier_union) # => {'jim', 'pam', 'jan', 'ryan', 'kelly', 'michael'}
group_intersection = group_1.intersection(group_2)
print(group_intersection) # => {'jim'}
easier_intersection = group_1 & group_2 # The same as the one above
print(easier_intersection) # => {'jim'}
If the symbols "
|" and "&" are unfamiliar to you (as seen ineasier_unionandeasier_intersection), check out the bitwise operators in the Operators post.
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Top comments (1)
are you programmer can you tech me please