python-set.rst

Set

Table of Contents

• Set comprehension
• Uniquify a List
• Union Two Sets
• Append Items to a Set
• Intersection Two Sets
• Common Items from Sets
• Contain
• Set Diff
• Symmetric diff

Set comprehension

>>> a = [1, 2, 5, 6, 6, 6, 7]
>>> s = {x for x in a}
>>> s
set([1, 2, 5, 6, 7])
>>> s = {x for x in a if x > 3}
>>> s
set([5, 6, 7])
>>> s = {x if x > 3 else -1 for x in a}
>>> s
set([6, 5, -1, 7])

Uniquify a List

>>> a = [1, 2, 2, 2, 3, 4, 5, 5]
>>> a
[1, 2, 2, 2, 3, 4, 5, 5]
>>> ua = list(set(a))
>>> ua
[1, 2, 3, 4, 5]

Union Two Sets

>>> a = set([1, 2, 2, 2, 3])
>>> b = set([5, 5, 6, 6, 7])
>>> a | b
set([1, 2, 3, 5, 6, 7])
>>> # or
>>> a = [1, 2, 2, 2, 3]
>>> b = [5, 5, 6, 6, 7]
>>> set(a + b)
set([1, 2, 3, 5, 6, 7])

Append Items to a Set

>>> a = set([1, 2, 3, 3, 3])
>>> a.add(5)
>>> a
set([1, 2, 3, 5])
>>> # or
>>> a = set([1, 2, 3, 3, 3])
>>> a |= set([1, 2, 3, 4, 5, 6])
>>> a
set([1, 2, 3, 4, 5, 6])

Intersection Two Sets

>>> a = set([1, 2, 2, 2, 3])
>>> b = set([1, 5, 5, 6, 6, 7])
>>> a & b
set([1])

Common Items from Sets

>>> a = [1, 1, 2, 3]
>>> b = [1, 3, 5, 5, 6, 6]
>>> com = list(set(a) & set(b))
>>> com
[1, 3]

Contain

b contains a

>>> a = set([1, 2])
>>> b = set([1, 2, 5, 6])
>>> a <= b
True

a contains b

>>> a = set([1, 2, 5, 6])
>>> b = set([1, 5, 6])
>>> a >= b
True

Set Diff

>>> a = set([1, 2, 3])
>>> b = set([1, 5, 6, 7, 7])
>>> a - b
set([2, 3])

Symmetric diff

>>> a = set([1,2,3])
>>> b = set([1, 5, 6, 7, 7])
>>> a ^ b
set([2, 3, 5, 6, 7])