Python's Path to growth 6--set

I. What is set

　　Set is an unordered, non-repeating sequence

Two. Create a set

(1) se={"123", "456"}

(2) li=[11,22,11,22]

Se=set (LI)

Then se={11,22}

Description: Set is a class, and the class name () is the __init__ method that executes the class.

Note: The second way to create a set representation in Python2 and Python3 is different.

1Admindemacbook-air-5: stu179471 admin$ python2Python 2.7.10 (default, Jul 14 2015, 19:46:27) 3[GCC 4.2.1 Compatible Apple LLVM 6.0 (clang-600.0.39)] on Darwin4Type" Help","Copyright","credits" or "License"  forMore information.5>>> li=[11,22,11,22]6>>> s1=set (LI)7>>>S18Set ([11, 22])9>>>exit ()TenAdmindemacbook-air-5: stu179471 admin$ python3 OnePython 3.5.1 (v3.5.1:37a07cee5969, Dec 5 2015, 21:12:44)  A[GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on Darwin -Type" Help","Copyright","credits" or "License"  forMore information. ->>> li=[11,22,11,22] the>>> s2=set (LI) ->>>S2 -{11, 22}

Python2 and Python3 differences

Three. Operation Set

1 S1.add () add an element2 S1.update (an iterative object) to add elements in bulk3 s1.difference (S2) exists in S1, and does not exist in S2, a new set is generated4 the intersection of s1.inetrsection (S2) S1 and S2 generates a new set5 s1.symmetric_difference (S2) S1 and S2 do not exist, symmetric difference sets, will generate a new set6 _update: The above three methods have their corresponding _update method (e.g.:d ifference_update ()), which does not generate a new set and is updated directly to S17 s1.union (S2) S1 and S28 s1.isdisjoint (S2) does not intersect, returns true9 s1.issubset (S2) S1 is a subset of S2 returns trueTen s1.issuperset (S2) S1 is the parent set of S2 returns True One Discard (Element) removes the specified element, no error is present A Remove (Element) ditto but not present will error -Pop () is randomly removed and gets the removed element

Four. Set small example

Implementation of the example shown

The code is as follows:

old_dict={    "#1": 8,    "#2": 4,    "#4": 2,}new_dict={    "#1": 4,    "#2": 4,    "#3": 2,}old_set=Set (Old_dict.keys ()) New_set=Set (New_dict.keys ()) Del_set=old_set.difference (new_set) Add_set=new_set.difference (old_set) Update_set=old_set.intersection (New_set) forIinchDel_set:old_dict.pop (i) forIinchAdd_set:old_dict[i]=New_dict[i] forIinchUpdate_set:old_dict[i]=New_dict[i]Print(old_dict)Print(new_dict)

Code

Five. Supplementary knowledge

　　Many classes have double-underline methods, the double-underline method generally has a special meaning,

For example:

li=[1,2,3,4] #list __init__

Li () #list __call__

Li[0] #list __getitem__

Li[0]=1 #list __setitem__

　　Del Li[0] #list __delitem__

Python's Path to growth 6--set