Detailed python set collection

Python collection, and a collection of mathematical concepts, like, to hold non-repeating elements, namely elements of the collection are unique, different from each other.

Formally, dictionaries and the like, Python will set all the elements in a pair of braces {} in use between adjacent elements "," separated, as shown below:

{Element1, element2, ..., elementN}

From the content point of view, the same collection, only store immutable data types, including plastic, float, string, tuple, can not be stored lists, dictionaries, a collection of these variable data types , otherwise Python interpreter throw a TypeError.

And to note that the data must be guaranteed to be unique, because for each set of data elements, will keep a

Python is provided a method of creating a set of two kinds of set, {} are used to create and use set () function to convert the list, and other types of data tuple set.

[root@kube set]# cat demo.py 
a = {1,2,1,'test','hi','test','one'}
print(type(a))
print(a)
[root@kube set]# py demo.py 
<class 'set'>
{'hi', 1, 2, 'one', 'test'}
[root@kube set]#

set1 = set("c.biancheng.net")
set2 = set([1,2,3,4,5])
set3 = set((1,2,3,4,5))
print("set1:",set1)
print("set2:",set2)
print("set3:",set3)

Note that if you want to create an empty set, only use the set () function to achieve. Because direct use of a pair {}, Python interpreter will treat this as an empty dictionary.

python access set collection element

Since the elements of the collection is disordered, and therefore can not use the index to access elements to the list that. Python, the access to the collection element The most common method is to use a cyclic structure, one by one to read out the data set.

[Kube the root @ SET] # CAT demo.py 
A = {1,2,1, ' Test ' , ' Hi ' , ' Test ' , ' One ' }
 Print (type (A))
 for ELE in A: # traversal See
     Print (ELE, End = ' - ' ) 

del A # delete
 Print (A) 
[the root @ Kube SET] # Py demo.py 
< class  ' SET ' > 
1--2 - Hi - Test - One -Traceback (most recent call last):
  File "demo.py", line 7, in <module>
    print(a)
NameError: name 'a' is not defined
[root@kube set]#

Python set set of basic operations (add, delete, intersection, union, difference)

Python the SET collection of the most common operation is to add to the collection, delete elements, as well as doing the intersection between the set and the union, difference and other operations, this section will explain one by one concrete realization of these operations.

[root@kube set]# cat demo1.py 
a = {1,2,'three','four',(5,6)}
b = {1,8,'th','fo',(5,6)}
c = {1,2,'three','four',(5,6)}
d = {1,8,'th','fo',(5,6)}
a.add('hi') #Add () function to add, each time it receives a parameter 
b.remove (( 5,6 )) #remove deleted, each receive only one parameter
 Print (A)
 Print (B) 
[the root @ Kube SET] # Py the demo1 .py 
{. 1, 2, ' Four ' , (. 5,. 6), ' Hi ' , ' Three ' } 
{ . 1,. 8, ' TH ' , ' FO ' } 
[@ Kube the root SET] #

Python set to do a collection of intersection, union, difference operation

In Figure 1, there are two sets, respectively set1 = {1,2,3} and set2 = {3,4,5}, they are both the same element, there are different elements. In these two sets, for example, are made of different calculation results are shown in Table 1.

Table 1 Python set operation set
Arithmetic operations	Operators Python	meaning	example
Intersection	&	Take two set of common elements	>>> set1 & set2 {3}
Union	\|	Take two set of all elements	>>> set1 \| set2 {1,2,3,4,5}
Difference set	-	Take a further element in the set is not set	>>> set1 - set2 {1,2} >>> set2 - set1 {4,5}
Symmetric difference	^	Taking a set of A and B does not belong to the elements of A & B	>>> set1 ^ set2 {1,2,4,5}

[Kube the root @ SET] # CAT demo1.py 
A = {1,2, ' Three ' , ' Four ' , (5,6 )} 
B = {1,8, ' TH ' , ' FO ' , (. 5, . 6 )}
 Print (a & B) # intersection of
 Print (a | B) # collection request
 Print (a - B) # differencing sets
 Print (a ^ B) # find symmetric difference is that in addition to all the rest of the intersection 
[Kube the root @ SET] # Py demo1.py 
{(. 5,. 6),. 1 } 
{ . 1, 2, ' Three ' , (. 5,. 6),. 8,'th', 'four', 'fo'}
{'four', 2, 'three'}
{'fo', 2, 'three', 'four', 8, 'th'}
[root@kube set]#