Python - How To Join Two Sets in Python

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In this tutorial, we will introduce different methods to join two .

  1. A |= B
  2. A.update(B)
  3. A.union(B)
  4. 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} 
Attention

reduce is the built-in 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.

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