This is a brief documentation on how to use sets in Python.

In Python, a set is a collection – i.e. a container which without indexing and withour order.

Sets are declared with {} brackets in Python

# defining a set with 5 elements
a = {"a","b","c","d","e"}

Sets are printable

# printing set a will also show you how they do NOT have any defined order
print(a)

{'c', 'e', 'd', 'b', 'a'}

Sets can contain different types of data

# sets can contain different datatypes
b = {1,"a",1.1}
print(b)

{1, 'a', 1.1}

Sets are iterable

# using for loop to print all elements of set b
for i in b:
    print(i)

1
a
1.1

You can add elements to a set using the .add() method

# adding an element to set b, using .add() method
b.add(-111)
print(b)

{1, -111, 'a', 1.1}

You can add multiple items to a set, using the .update() method

# adding three new elements to set b, using .update()
b.update([1,2,3])
print(b)

{1, 2, 1.1, 3, -111, 'a'}

As with Python lists, the length of a set equals the number of elements and is determined using the len() function

# determining the length of set b
len(b)

6

Elements can be removed from a set, using the .remove() method

# removing element with value "a" from set b
b.remove("a")
print(b)

{1, 2, 1.1, 3, -111}

Sets cannot contain duplicates

# delcaring a set with duplicates; duplicates will be ignored
c = {"a","a","a"}
# printing set c will show that duplicates have been automatically removed from the set
print(c)

{'a'}

.clear() will clear a set from its content

# clearing set b, using .clear()
b.clear()
print(b)

set()

Empty sets can be declared using set()

# delcaring empty set, using set() constructor
d = set()
# printing empty set d
print(d)
# checking type of d, to confirm that it is a set
type(d)
# add element with value "a"
d.add("a")
# print set after having added the additional element
print(d)

set()
{'a'}

A set can be entirely deleted, usign the del keyword

# deleting set d
del d
# trying to print d; this will return a traceback
print(d)

---------------------------------------------------------------------------
NameError                                 Traceback (most recent call last)
<ipython-input-51-38cd230d9bf2> in <module>
      2 del d
      3 # trying to print d; this will return a traceback
----> 4 print(d)

NameError: name 'd' is not defined

Sets can be joined, using .union()

# defining two new sets, e and f
e = {"a","b","c"}
f = {1,2,3}
# joining the two sets (merging) and printing the merged set
print(e.union(f))

{'c', 1, 2, 3, 'b', 'a'}

Other important containers are e.g. Python dictionaries and Python lists.

Linnart Felkl

Data scientist focusing on simulation, optimization and modeling in R, SQL, VBA and Python