How to join two sets in Python

A = B
to join two sets in Python 
A.update(B)
to join two sets in Python 
A.union(B)
to join two sets in Python 
reduce(operator.or_, [A, B])
to join two sets in Python
In this tutorial, we will introduce different methods to join two sets in Python.
A = B
A.update(B)
A.union(B)
reduce(operator.or_, [A, B])
A = B
to join two sets in Python
A = B
adds all elements of set B
to set A
.
>>> A = {4, 5, 6, 7}
>>> B = {6, 7, 8, 9}
>>> A = B
>>> A
{4, 5, 6, 7, 8, 9}
A.update(B)
to join two sets in Python
A.update(B)
method is identical to A = B
. It modifes set A
in place.
>>> A = ["a", "b", "c"]
>>> B = ["b", "c", "d"]
>>> A.update(B)
>>> A
["a", "b", "c", "d"]
A.union(B)
to join two sets in Python
A.union(B)
returns the union of sets A
and B
. It doesn’t modify set A
in place but returns a new set.
>>> A = {4, 5, 6, 7}
>>> B = {6, 7, 8, 9}
>>> A.union(B)
{1, 2, 3, 4, 5, 6}
>>> A
{1, 2, 3, 4}
It is identical to A  B
.
reduce(operator.or_, [A, B])
to join two sets in Python
operator.or_(A, B)
returns the bitwiser or
of A
and B
, or union of sets
A
and B
if A
and B
are sets.
reduce
in Python 2.x or functools.reduce
in both Python 2.x and 3.x applies function to the items of iterable.
Therefore, reduce(operator.or_, [A, B])
applies or
function to A
and B
. It is the identical to the Python expression A  B
>>> import operator
>>> from functools import reduce
>>> A = {4, 5, 6, 7}
>>> B = {6, 7, 8, 9}
>>> reduce(operator.or_, [A, B])
{4, 5, 6, 7, 8, 9}
reduce
is the builtin function in Python 2.x, but is deprecated in Python 3.
Therefore, we need to use functools.reduce
to make the codes compatible in Python 2 and 3.