Append values to a set in Python

Define a set

a = set()

Use add to append single values

a.add(1)
a.add(2)

Use update to add elements from tuples, sets, lists or frozen-sets

a.update([3, 4])

>>> print(a)
{1, 2, 3, 4}

Note: Since set elements must be hashable, and lists are considered mutable, you cannot add a list to a set. You also cannot add other sets to a set. You can however, add the elements from lists and sets as demonstrated with the .update method.

your_set.update(your_sequence_of_values)

e.g, your_set.update([1, 2, 3, 4]). Or, if you have to produce the values in a loop for some other reason,

for value in ...:
    your_set.add(value)

But, of course, doing it in bulk with a single .update call is faster and handier, when otherwise feasible.