? ? ? 全局變量(global variable)是那些未在任何函數內部定義并且具有全局作用域的變量，而局部變量(local variable)是那些在函數內部定義并且其作用域僅限于該函數的變量。換句話說，我們可以說局部變量只能在初始化它的函數內部訪問，而全局變量在整個程序和每個函數內部都可以訪問。

? ? ? global關鍵字：如果我們要進行賦值或更改全局變量，我們只需要在函數中使用global關鍵字。打印和訪問全局變量不需要global關鍵字。如果在函數內部更改或創建的任何變量尚未聲明為全局變量，則它都是局部變量。在函數外使用global關鍵字無效。global綁定全局變量。

? ? ? nonlocal關鍵字：與global關鍵字功能相似，但用于嵌套函數(nested function)中。nonlocal綁定局部變量，只對局部起作用，離開嵌套函數，那么該變量則無效。

? ? ? 以上內容主要參考：https://www.geeksforgeeks.org/global-local-variables-python/

? ? ? 以下為測試代碼：

var = 6if var == 1:# reference: https://www.geeksforgeeks.org/global-local-variables-python/def f(): # Creating local variabless = "I love Geeksforgeeks" # local vairableprint("Inside Function:", s)f()#print("s:", s) # NameError: name 's' is not defined
elif var == 2:# reference: https://www.geeksforgeeks.org/global-local-variables-python/# Defining and accessing global variablesdef f(): # This function uses global variable sprint("Inside Function:", s)# Global scopes = "I love Geeksforgeeks" # global variable,  is used both inside the f function as well as outside the f functionf()print("Outside Function:", s)
elif var == 3:# reference: https://www.geeksforgeeks.org/global-local-variables-python/# This function has a variable with name same as sdef f():#s += 'GFG' # UnboundLocalError: local variable 's' referenced before assignments = "Me too." # 如果在函數作用域內也定義了同名變量,那么它將僅打印函數內部給出的值,而不是全局值print(s)s = "I love Geeksforgeeks" # global scopef()print(s) # I love Geeksforgeeks
elif var == 4:# reference: https://www.geeksforgeeks.org/global-local-variables-python/# This function modifies the global variable 's'def f():global s # 如果我們要進行賦值或更改全局變量,我們只需要在函數中使用global關鍵字s += ' GFG'print(s)s = "Look for Geeksforgeeks Python Section"print(s)s = "Python is great!" # global scopef()print(s) # Look for Geeksforgeeks Python Section
elif var == 5:# reference: https://www.geeksforgeeks.org/use-of-nonlocal-vs-use-of-global-keyword-in-python/def fun():var1 = 10def gun():nonlocal var1 # tell python explicitly that it has to access var1 initialized in fun using the keyword nonlocal# global var1; var1 = var1 + 10 # NameError: name 'var1' is not definedvar1 = var1 + 10print(var1) # 20gun()print(var1) # 20fun()
elif var == 6:# reference: https://www.geeksforgeeks.org/python-nonlocal-keyword/def geek_func():geek_name = "geekforgeeks" # local variable to geek_funcdef geek_func1(): # First Inner functiongeek_name = "GeekforGeeks"def geek_func2(): # Second Inner functionnonlocal geek_name # Declairing nonlocal variablegeek_name = 'GEEKSFORGEEKS'print(geek_name) # Printing our nonlocal variable, GEEKSFORGEEKSgeek_func2() # Calling Second inner functiongeek_func1() # Calling First inner functionprint(geek_name) # Printing local variable to geek_func, geekforgeeksgeek_func()
print("test finish")

? ? ? GitHub：https://github.com/fengbingchun/Python_Test

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