Usage followed the project to learn python (a) basic skills of a global variable

　　Period of time without using python to write code, I found a lot of previous learning grammar forget. It seems the original aspects of the project to do good enough, there is no systematic use and learning, leading to a lot of grammar can not facile. In this next project,

Some python knowledge unfamiliar places there are sure to encounter forgotten to re-comb, on python to achieve flexibility in the use of state, can not simply be able to knock code to achieve learn, do, teach the three-in-one. That is, learning by doing, learning to do, do teach, teach in secondary schools

realm.

 

　　The scope of global variables:

　　In vitro function generally be a global variable defined variables, variables inside a function defined is referred to as local variables. Global variables are available all scopes, local variables can be used in this function, order of use is variable, local variable> global variable, that is to say: the priority use of local variables

 

　　global keyword:

　　In order to solve the problem using global variables within a function, python increased global keyword, use its features, you can specify the scope of variables.

The role of global keyword: var variable declaration is global

 

     Example one: the assignment function can not change the value of the global variables:

 1 global val
 2 val = 10
 3 
 4 def test1():
 5         global val
 6         val = 5
 7         print('test1 global val:',val)
 8 
 9 def test2():
10         val = 8
11         print('test2 global val:',val)
12 class Test():
13         def __init__(self):
14                 #global val
15                 val = 5
16                 #zoo()
17                 #xy()
18         def connect(self):
19                 print("class in connect global val:",val)
20                 if 5 == val:
21                         print("global val is:",val)
22 
23 if __name__=="__main__":
24         Test().connect()

View Code

 

　　operation result:

class in connect global val: 10

　　It can be seen in the function assignment does not change the value of a global variable, we need global keyword

 

　　Example Two: global variable value change must be global Keywords:

　　Shen Fu

global val
val = 10

def test1():
        global val
        val = 5
        print('test1 global val:',val)

def test2():
        val = 8
        print('test2 global val:',val)
class Test():
        def __init__(self):
                #global val
                val = 5
                test1()
                test2()
        def connect(self):
                print("class in connect global val:",val)
                if 5 == val:
                        print("global val is:",val)

if __name__=="__main__":
        Test().connect()

View Code

   Test Results:

　　test1 global val: 5
　　test2 global val: 8
　　class in connect global val: 5
　　global val is: 5

As can be seen, changes in the value of a global variable, there must be global keyword. Otherwise it is treated as a local variable. This is sure to write well.