Python Learning Notes (8th lesson)

In this section we will learn another Python data type: Collection (set)

1. Set (SET)

A collection in Python is an unordered data type with no duplicate elements and cannot be indexed to refer to elements in the collection

>>> basket = [' apple ', ' orange ', ' apple ', ' pear ', ' orange ', ' banana ']>>> set (basket) set ([' Orange ', ' pear ', ' apple ', ' banana ') 

Set1-set2 to get an element in the Set1 element that does not exist in Set2, returns a new collection. This function is the same as the Set1.difference (Set2) effect

>>> F=set ([1,2,3,4,5]) >>> c=set ([3,4,5,6]) >>> f.difference (c) Set ([1, 2] ) >>> list (f) [1, 2, 3, 4, 5]>>> Fcset ([1, 2])      

Set1|set2 gets the element in Set1 or Set2, returns a new collection

>>> F=set ([1,2,3,4,5]) >>> c=set ([3,4,5,6]) >>> f|  Cset ([1, 2, 3, 4, 5, 6])  

Set1&set2 gets the elements that exist in both Set1 and Set2, returning a new collection

>>> F=set ([1,2,3,4,5]) >>> c=set ([3,4,5,6]) >>> f&Cset ([3, 4, 5]) 

Set1^set2 gets the element that exists in Set1 or Set2, but does not include both in Set1 and Set2, and returns a new collection

>>> F=set ([1,2,3,4,5]) >>> c=set ([3,4,5,6]) >>> f^Cset ([1, 2, 6])  

2. Functions of the collection

Set.add (x) Adds an element x that is not added to the collection if X is already present in the collection

>>> F=set ([3,4,5,6])>>> f.add ('a')>>> Fset (['a', 3, 4, 5, 6])>>> f.add ('a ' )>>> fset (['a', 3, 4, 5, 6])

Set.clear () emptying the collection

>>> F=set ([3,4,5,6])>>> f.clear ()>>> fset ([])

Set.copy () Copy a collection

>>> F=set ([3,4,5,6])>>> s=f.copy ()>>> sset ([3, 4, 5, 6])

Set1.difference (Set2) Gets the element in the Set1 that does not exist in the Set2, and returns a new collection. Same as Set1-set2

>>> F=set ([3,4,5,6])>>> s=set ([1,2,3,4,5])>>> s.difference (f) Set ([1, 2])

Set1.difference_update (Set2) updates the Set1 so that Set1=set1-set2

>>> S=set ([1,2,3,4,5])>>> s.difference_update (f)>>> sset ([1 , 2])

Set.discard (x) Delete the element with the value x in the collection

>>> S=set ([1,2,3,4,5])>>> S.discard (3)>>> sset ([1, 2, 4, 5])

Set1.intersection (Set2) returns elements that exist in both Set1 and Set2, with the same effect as Set1&set2

>>> F=set ([3,4,5,6])>>> s=set ([1,2,3,4,5])>>> f.intersection (s) Set ([3, 4, 5])

Set1.intersection_update (set2) update Set1 so that Set1 equals Set1^set2

>>> F=set ([3,4,5,6])>>> s=set ([1,2,3,4,5])>>> F.intersection_ Update (s)>>> fset ([3, 4, 5])

Set1.isdisjoint (Set2) determines if Set1 and Set2 have the same element, if any, returns false, does not return true

>>> F=set ([3,4,5,6])>>> s=set ([1,2,3,4,5])>>> q=set ([1, 0]) >>> F.isdisjoint (s) False>>> f.isdisjoint (q) True

Set1.issubset (Set2) determines if Set1 is a subset of Set2, returns True if yes, otherwise false

>>> F=set ([up])>>> q=set ([3,4,5,6,7])>>> s=set ([1,2,3,4,5]) >>> f.issubset (q) False>>> f.issubset (s) True

Set1.issuperset (Set2) determines whether Set1 contains Set2, that is, whether Set2 is a subset of Set1, and if so, returns true, otherwise false

>>> F=set ([up])>>> s=set ([1,2,3,4,5])>>> f.issuperset (s) False >>> S.issuperset (f) True

Python Learning Notes (8th lesson)