Python Set union(): Method and | Operator Examples

A.union(B) returns a new set containing all distinct elements from the inputs. The | operator is the set-to-set equivalent; duplicates are naturally stored only once.

union() can accept iterable arguments, whereas | requires set-like operands. If you want to change an existing set instead, use update(). See the Set operations overview.

Set order: sets are unordered. Whenever an example prints a set, the displayed element order can differ between runs or Python environments.

Video Tutorial on Set

union using | operator

All distinct elements from both sets
Using the vertical bar (|) operator

A={1,2,3}
B={3,4,5}
print(A|B)

Output ( Note 3 is used once only )

{1, 2, 3, 4, 5}

Using union() method

A={'a','b','c'}
B={'a','y','z'}
print(A.union(B))

Output

{'z', 'c', 'a', 'y', 'b'}

Using More Than Two Sets

We can use any number of sets with union()

A={'a','b','c'}
B={'a','y','z'}
C={'a','k','l'}
print(A | B |C)

Output

{'z', 'l', 'k', 'c', 'a', 'y', 'b'}

union() method

Using string ( iterable object ) with union() method

A={'a','b','c','x','y'}
B='Alex'
print(A.union(B))

Output

{'l', 'e', 'A', 'a', 'c', 'x', 'y', 'b'}

The | operator requires set-like operands. The union() method can accept an iterable such as a list or string.

Using list with union() method.

A={'a','b','c'}
B=['a','x','y']
print(A.union(B))

Output

{'c', 'x', 'y', 'a', 'b'}

Below code will generate error.

print(A | B)

 TypeError: unsupported operand type(s) for |: 'set' and 'list'

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Python Set union() Method

Video Tutorial on Set

union using | operator

Using More Than Two Sets

union() method

Subhendu Mohapatra