Python之global

Terminal

1　　Global

　　The global statement and its nonlocal cousin are the only things that are remotely like declaration statements in Python. They are not type or size declarations; they are namespace declarations. The global statement tells Python that a function plans to change one or more global names.

　　• Global names are variables assigned at the top level of the enclosing module file.
　　• Global names must be declared only if they are assigned within a function.
　　• Global names may be referenced within a function without being declared.

　　In other words, global allows us to change names that live outside a def at the top level of a module file.



2　　Example

　　The global statement consists of the keyword global, followed by one or more names separated by commas.

1. X = 88                         # Global X
   
2. 
   
3. def func():
   
4.     global X
   
5.     X = 99                     # Global X: outside def
   
6. 
   
7. func()
   
8. print(X)                       # Prints 99

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1. y, z = 1, 2                    # Global variables in module
   
2. 
   
3. def all_global():
   
4.     global x                   # Declare globals assigned
   
5.     x = y + z                  # No need to declare y, z: LEGB rule

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x, y, and z are all globals inside the function all_global. y and z are global because they aren’t assigned in the function; x is global because it was listed in a global statement to map it to the module’s scope explicitly. Without the global here, x would be considered local by virtue of the assignment.



3　　Access globals

1. # thismod.py
   
2. var = 99                              # Global variable == module attribute
   
3. 
   
4. def local():
   
5.     var = 0                           # Change local var
   
6. 
   
7. def glob1():
   
8.     global var                        # Declare global (normal)
   
9.     var += 1                          # Change global var
   
10. 
    
11. def glob2():
    
12.     var = 0                           # Change local var
    
13.     import thismod                    # Import myself
    
14.     thismod.var += 1                  # Change global var
    
15. 
    
16. def glob3():
    
17.     var = 0                           # Change local var
    
18.     import sys                        # Import system table
    
19.     glob = sys.modules['thismod']     # Get module object (or use __name__)
    
20.     glob.var += 1                     # Change global var
    
21. 
    
22. def test():
    
23.     print(var)
    
24.     local();
    
25.     print(var)
    
26.     glob1();
    
27.     print(var)
    
28.     glob2();
    
29.     print(var)
    
30.     glob3()
    
31.     print(var)
    

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run and get results

1. >>> import thismod
   
2. >>> thismod.test()
   
3. 99
   
4. 99
   
5. 100
   
6. 101
   
7. 102

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substr函数

一直都不知道还有这个方法 看到这个帖子才知道 谢谢

import thismod                    # Import myself
import sys                        # Import system table
glob = sys.modules['thismod']     # Get module object (or use __name__)

呵呵，也偷偷的学习一下

script ==> thismod.py