brief introduction ：
Case study 1： Global cannot use local variables .
Case study 2： Global variables , Any range can be used .
Case study 3： A local variable defined in a function
Case study 4： Between functions global The role of keywords
Case study 5： In different file modules global, Be careful test6, test7 For different files .
Case study 6： In different file modules global, Be careful test6, test7 For different files .
attach ： use global Declaration of multiple variables needs to be separated by commas
Conclusion ：
brief introduction ：1、global yes Python Global variable keywords in .
2、 Global variables are a kind of programming terminology , From variables .
3、 Variables are divided into local and global , Local variables can also be called internal variables .
4、 Variables created by an object or function are usually local variables , Can only be quoted internally , It cannot be referenced by other objects or functions .
5、 Global variables can be created by some object function , It can also be created anywhere in this program . Global variables can be referenced by all objects or functions in this program .
6、global Keyword is used to make a local variable a global variable .
Case study 1： Global cannot use local variables .
# -*- coding: utf-8 -*-def test1(): # local variable local local_var = "a" print(local_var)# Global cannot use local variables , Only the corresponding local scope is available # print(local_var) # NameError: name 'local_var' is not defined Case study 2： Global variables , Any range can be used .global_var = 1def test2(): # Use global variables in functions print(global_var + 1) def inner(): # Use global variables within nested functions print(global_var + 2) return global_var + 3 # Global variables are used in the return value # Use global variables outside the function .print(global_var) Case study 3： A local variable defined in a function def test3(): # Variables within a function , But for subordinate functions, they are global variables , Externally, it is a local variable func_var = 1 def inner(): print(func_var) return func_var return inner()test3() Case study 4： Between functions global The role of keywords def test4(): # global Key role global func_var func_var = 2 # call test5 You can print func_var, Get rid of global Will report a mistake . test5() print(test5.__globals__)def test5(): print(func_var)test4() Case study 5： In different file modules global, Be careful test6, test7 For different files .# a.pydef test6(): # global Key role global func_var func_var = 3# b.pyfrom a import test6def test7(): print(test6.__globals__["func_var"])# Don't do it first test6 In this case, an exception is thrown .KeyError: 'func_var'test7() # KeyError: 'func_var' Case study 6： In different file modules global, Be careful test6, test7 For different files .# a.pydef test6(): # global Key role global func_var func_var = 4# b.pyfrom a import test6def test7(): print(test6.__globals__["func_var"])# Execute first test6 Under the circumstances ,test have access to func_vartest6()test7() # 4 attach ： use global Declaration of multiple variables needs to be separated by commas num = 0def cc(): global count,num count = count+1 num = num+2 print(count,num)cc()3 2# You can use... In a function global Declare the ability to modify global variables numOut[24]: 2# countOut[25]: 3 When using global variables , You can also use class variables instead of class C: count = 3def cc(): count = C.count+1 print(count)cc()4 Conclusion ：1、 Import packages only ,global The defined global variable is not added to globals Inside .
2、 perform global The corresponding function ,global The defined function will store the corresponding variables , Other functions do not store .
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Xiaobai Learning Python Series——【Day44】Encapsulation and Polymorphism of the Three Characteristics of Object-Oriented; Object-Oriented Reflection
今日內容概要A practical exercise of
