在函數內部定義變量時，他們與函數外部具有相同名稱的其他變量沒有任何關系，即變量名稱對于函數來說是局部的，這稱為變量的作用域，示例如下：

def func_local(x):print 'x is', xx = 2print 'Chanaged local x to',xx = 50 func_local(x) print 'x is still', x

?執行結果：

x is 50 Chanaged local x to 2 x is still 50

如果想在函數內部改變函數外的變量值，用global語句完成

def func_global():global yprint 'y is', yy = 50print 'Changed local y to', yy = 10 func_global() print 'Value of y is', y
def func_global():global yprint 'y is', yy = 50print 'Changed local y to', yy = 10 func_global() print 'Value of y is', y

執行結果：

y is 10 Changed local y to 50 Value of y is 50
y is 10 Changed local y to 50 Value of y is 50

函數參數若是list、set、dict可變參數，在函數內改變參數，會導致該參數發生變化，例如：

def func_local(x):print 'x is', xx.append(10)print 'Chanaged local x to',xx = range(6) func_local(x) print 'x is', x
def func_local(x):print 'x is', xx.append(10)print 'Chanaged local x to',xx = range(6) func_local(x) print 'x is', x

執行結果

x is [0, 1, 2, 3, 4, 5] Chanaged local x to [0, 1, 2, 3, 4, 5, 10] x is [0, 1, 2, 3, 4, 5, 10]
x is [0, 1, 2, 3, 4, 5] Chanaged local x to [0, 1, 2, 3, 4, 5, 10] x is [0, 1, 2, 3, 4, 5, 10] def func_local(x):print 'x is', xx.add(10)print 'Chanaged local x to',xx = set(range(6)) func_local(x) print 'x is', x
def func_local(x):print 'x is', xx.add(10)print 'Chanaged local x to',xx = set(range(6)) func_local(x) print 'x is', x

執行結果：

x is set([0, 1, 2, 3, 4, 5]) Chanaged local x to set([0, 1, 2, 3, 4, 5, 10]) x is set([0, 1, 2, 3, 4, 5, 10])
x is set([0, 1, 2, 3, 4, 5]) Chanaged local x to set([0, 1, 2, 3, 4, 5, 10]) x is set([0, 1, 2, 3, 4, 5, 10]) def func_local(x):print 'x is', xx['x'] = 2print 'Chanaged local x to',xx = dict([('x',1), ('y', 2)]) func_local(x) print 'x is', x
def func_local(x):print 'x is', xx['x'] = 2print 'Chanaged local x to',xx = dict([('x',1), ('y', 2)]) func_local(x) print 'x is', x

執行結果：

x is {'y': 2, 'x': 1} Chanaged local x to {'y': 2, 'x': 2} x is {'y': 2, 'x': 2}
x is {'y': 2, 'x': 1} Chanaged local x to {'y': 2, 'x': 2} x is {'y': 2, 'x': 2}
def func_local(x):print 'x is', xx = (4, 5, 6)print 'Chanaged local x to',xx = (1,2,3,) func_local(x) print 'x is', x def func_local(x):print 'x is', xx = (4, 5, 6)print 'Chanaged local x to',xx = (1,2,3,) func_local(x) print 'x is', x

執行結果

x is (1, 2, 3) Chanaged local x to (4, 5, 6) x is (1, 2, 3) x is (1, 2, 3) Chanaged local x to (4, 5, 6) x is (1, 2, 3)

若傳入可變參數如list、set、dict，在函數內部對參數做出修改，參數本身發生變化，tuple、str不變

轉載于:https://www.cnblogs.com/Bella2017/p/7994572.html

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