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## Python Programming – Set Methods

**Set methods**

Below are the methods of both set and frozenset objects. Note that the non-operator versions of these methods accept any iterable as an argument, while their operator-based counterparts require their arguments to be set (set and frozenset).

isdisjoint ( other )

Return True, if the set has no elements in common with other. Sets are disjoint, if and only if their intersection is the empty set.

>>> s1=set ( [ 5 , 10 , 15 , 20] ) >>> s2=set ( [ 30 , 35 , 40 ] ) >>> s1 . isdisjoint ( s2 ) True >>> s1=frozenset ( [ 5 , 10 , 15 , 20 ] ) >>> s2=frozenset ( [ 30 , 35 , 40 ] ) >>> s1 . isdisjoint ( s2 ) True >>> s1=set ( [ 5 , 10 , 15 , 20 ] ) >>> s2=frozenset ( [30 , 35 , 40 ] ) >>> s1 . isdisjoint ( s2 ) True

issubset ( other )

Test whether every element in the set is in other.

>>> s1=set ( [ 5 , 15 ] ) >>> s2=set ( [ 5 , 10 , 15 , 20 ] ) >>> s1 . issubset ( s2 ) True >>> s1 . issubset ( ( 5 , 10 , 15 , 20 ) ) True >>> s1=frozenset ( [ 5 , 15 ] ) >>> s2=frozenset ( [ 5 , 10 , 15 , 20 ] ) >>> s1 . issubset ( s2 ) True >>> s1 . issubset ( ( 5 , 10 , 15 , 20 ) ) True

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The operator based version of the above method is set<=other.

>>> s1=set ( [ 5 , 15 ] ) >>> s2=frozenset ( [ 5 , 10 , 15 , 20 ] ) >>> s1<=s2 True

The operator based version setcother test whether the set is a proper subset of other, that is, set<=other and set!=other.

>>> s1=set ( [ 5 , 15 ] ) >>> s2=frozenset ( [ 5 , 10 , 15 , 20 ] ) >>> s1<s2 True

issuperset (other).

Test whether every element in other is in the set.

>>> s1=set ( [ 5 , 15 ] ) >>> s2=set ( [ 5 , 10 , 15 , 20 ] ) >>> s2 . issuperset ( s1 ) True >>> s2 . issuperset ( ( 5 , 15 ) ) True >>> s1=frozenset ( [ 5 , 15 ] ) >>> s2=frozenset ( [ 5 , 10 , 15 , 20 ] ) >>> s2 . issuperset ( s1 ) True >>> s2 . issuperset ( ( 5 , 15 ) )

The operator based version of the the above method is set >=other.

>>> s1=set ( [ 5 , 15 ] ) >>> s2=frozenset ( [ 5 , 10 , 15 , 20 ] ) >>> s1>=s2 False

The operator-based version set> another test whether the set is a proper superset of other, that is, set>=other and set! =other.

>>> s1=set ( [ 5 , 15 ] ) >>> s2=frozenset ( [ 5 , 10 , 15 , 20 ] ) >>> s1<s2 False

union ( other, . . . )

Return a new set with elements from the set and all others.

>>> s1=set ( [ 5 , 15 ] ) >>> s2= [ 15 , 20 , 25 ] >>> s3=frozenset ( [ 30 , 35 , 40 ] ) >>> s1 . union ( s2 , s3 ) set ( [ 35 , 20 , 5 , 40 , 25 , 30 , 15 ] )

The operator based version of the above method is set | other. . .

>>> s1=set ( [ 5 , 15 ] ) >>> s2=set ( [ 15 , 20 , 25 ] ) >>> s3=frozenset ( [ 30 , 35 , 40 ] ) >>> s1 | s2 | s3 set ( [ 35 , 20 , 5 , 40 , 25 , 30 , 15 ] )

intersection ( other , . . .)

Return a new set with elements common to the set and all others .

>>> s1=set ( [ 5 , 10 , 15 ] ) >>> s2= [ 15 , 20 , 25 , 10 ] >>> s3=frozenset ( [ 30 , 15 , 35 , 40 , 10 ] ) >>> s4= ( 40 , 50 , 10 , 15 , 20 ) >>> si . intersection ( s2 , s3 , s4 ) set ( [ 10 , 15 ] )

The operator based version of the above method is set&other . . .

>>> s1=set ( [ 5 , 10 , 15] ) >>> s2=set ( [ 15 , 20 , 25 , 10 ] ) >>> s3=frozenset ( [ 30 , 15 , 35 , 40 , 10 ] ) >>> s4=frozenset ( [ 40 , 50 , 10 , 15 , 20 ] ) >>> s1&s2&s3&s4 set ( [ 10 , 15 ] )

difference ( other, . . . )

Return a new set with elements in the set that are not in the others.

>>> s1=set ( [ 5 , 10 , 15 ] ) >>> s2= [ 15 , 20 , 25 , 10 ] >>> s3=frozenset ( [ 30 , 15 , 35 , 40 , 10 ] ) >>> s4= ( 40 , 50 , 10 , 15 , 20 ) >>> s3.difference ( s1 , s2 , s4 ) frozenset ( [ 35 , 30 ] )

The operator based version of the above method is set-other- . . .

>>> s1-set ( [ 5 , 10 , 15 ] ) >>> s2=set ( [ 15 , 20 , 25 , 10 ] ) >>> s3=frozenset ( [ 30 , 15 , 35 , 40 , 10 ] ) >>> s4=frozenset ( [ 40 , 50 , 10 , 15 , 20 ] ) >>> s1 - s2 - s3 - s4 set ( [ 5 ] ) >>> s3 - s1 - s2 - s4 frozenpet ( [ 35 , 30 ] )

symmetric_difference ( other )

Return a new set with elements in either the set or other but not both.

>>> s1=set ( [ 5 , 10 , 15 ] ) >>> s2= [ 15 , 20 , 25 , 10 ] >>> s1 . symmetric_difference ( s2 ) set ( [ 25 , 20 , 5 ] )

The operator based version of the the above method is set Aother.

>>> s1=set ( [ 5 , 10 , 15 ] ) >>> s2=frozenset ( [ 15 , 20 , 25 , 10 ] ) >>> s1∧ s2 set ( [ 25 , 20 , 5 ] ) >>> s2∧s1 frozenset ( [ 25 , 20 , 5 ] )

copy ( )

Return a copy of the set.

>>> s=set ( [ 5 , 10 , 15 , 20 ] ) >>> a=s.copy ( ) >>> a set ( [ 10 , 20 , 5 , 15 ] ) >>> s=frozenset ( [ 5 , 10 , 15 , 20] ) >>> a=s.copy ( ) >>> a frozenset ( [ 10 , 20 , 5 , 15 ] )

The following methods are available for set and do not apply to immutable instances of frozenset.

update ( other , . . . )

Update the set, adding elements from all others.

>>> s1=set ( [ 5 , 15 ] ) >>> s2= ( 15 , 20 , 25 ) >>> s3=frozenset ( [ 30 , 35 , 40] ) >>> s1 . update ( s2 , s3 ) >>> s1 set ( [ 35 , 20 , 5 , 40 , 25 , 30 , 15 ] )

The operator based version of the above method is set | =other | . . .

>>> s1=set ( [ 5 , 15 ] ) >>> s2=set ( [ 15 , 20 , 25 ] ) >>> s3=frozenset ( [ 30 , 35 , 40 ] ) >>> s1|= s2 | s3 >>> s1 set ( ' [ 35 , 5 , 40 , 15 , 20 , 25 , 30 ] )

intersection_update ( other , . . .)

Update the set, keeping only elements found in it and all others.

>>> s1=set ( [ 5 , 10 , 15 ] ) >>> s2= [ 15 , 20 , 25 , 10 ] >>> s3=set ( [ 30 , 15 , 35 , 40 , 10 ] ) >>> s4= ( 40 , 50 , 10 , 15 , 20 ) >>> s1 . intersection_update ( s2 , s3 , s4 ) >>> s1 set ( [ 10 , 15 ] )

The operator based version of the the above method is set&=other& . . .

>>> s1=set ( [ 5 , 10 , 15] ) >>> s2=set ( [ 15 , 20 , 25 , 10] ) >>> s3=frozenset ( [ 30 , 15 , 35 , 40 , 10 ] ) >>> s4=frozenset ( [ 40 , 50 , 10 , 15 , 20 ] ) >>> s1&=s2&s3&s4 >>> s1 set ( [10 , 15 ] )

difference_update(other, . . .)

Update the set, removing elements found in others.

>>> s1=frozenset ( [ 5 , 10 , 15 ] ) >>> s2= [ 15 , 20 , 25 , 10 ] >>> s3=set ( [ 30 , 15 , 35 , 40 , 10 ] ) >>> s4= ( 40 , 50 , 10 , 15 , 20 ) >>> s3 . difference_update ( s1 , s2 , s4 ) >>> s3 set ( [ 35 , 30 ] )

The operator based version of the above method is set-=other | . . .

>>> s1=frozenset ( [ 5 , 10 , 15 ] ) >>> s2=frozenset ( [ 15 , 20 , 25 , 10 ] ) >>> s3=set ( [ 30 , 15 , 35 , 40 , 10 ] ) >>> s4=frozenset ( [ 40 , 50 , 10 , 15 , 20 ] ) >>> s3-=s1 | s2 | s4 >>> s3 set ( [ 35 , 30 ] )

symmetric_difference_update(other)

Update the set, keeping only elements found in either set, but not in both.

>>> s1=set ( [ 5 , 10 , 15 ] ) >>> s2= [ 15 , 20 , 25 , 10 ] >>> s1 . symmetric_dif ference_update ( s2 ) >>> s1 set ( [ 25 , 20 , 5 ] )

The operator based version of the the above method is set/’=other.

>>> s1=set ( [ 5 , 10 , 15 ] ) >>> s2=frozenset ( [ 15 , 20 , 25 , 10 ] ) >>> s1 A=s2 >>> s1 set ( [ 25 , 20 , 5 ] )

add ( elem )

The method adds element elem to the set.

>>> s=set ( [ 5 , 10 , 15 , 20 ] ) >>> s.add ( 25 ) >>> s set ( [ 25 , 10 , 20 , 5 , 15 ] )

remove ( elem )

Remove element elem from the set. Raises KeyError, if elem is not contained in the set.

>>> s=set ( [ 5 , 10 , 15 , 20 ] ) >>> s.remove ( 15 ) >>> s set ( [ 10 , 20 , 5 ] ) >>> s=set ( [ 5 , 10 , 15 , 20 ] ) >>> s . remove ( 100 ) Traceback ( most recent call last ) : File " <stdin> " , line 1 , in <module> KeyError: 100

discard ( elem )

Remove element elem from the set if it is present. It is difference from remove () in a way that it does not raise KeyError if elem is not present in the set.

>>> s=set ( [ 5 , 10 , 15 , 20 ] ) >>> s . discard ( 15 ) >>> s set ( [ 10 , 20 , 5 ] ) >>> s . discard ( 100 ) >>> s set ( [ 10 , 20 , 5 ] )

pop ( )

Remove and return an arbitrary element from the set. Raises KeyError, if the set is empty.

>>> s=set ( [ 5 , 10 , 15 , 20] ) >>> s . pop ( ) 10 >>> s set ( [ 20 , 5 , 15 ] ) >>> s . pop ( ) 20 >>> s set ( [ 5 , 15 ] )

clear ( )

Remove all elements from the set.

>>> s=set ( [ 5 , 10 , 15 , 20 ] ) >>> s . clear ( ) >>> s set ( [ ] )