python-global全域變數

標籤：若是   cal   bsp   變化   關係   oba   hang   bar   aced   

在函數內部定義變數時，他們與函數外部具有相同名稱的其他變數沒有任何關係，即變數名稱對於函數來說是局部的，這稱為變數的範圍，樣本如下：

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

 執行結果：

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

如果想在函數內部改變函數外的變數值，用global陳述式完成

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

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

執行結果：

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

y is 10Changed local y to 50Value 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‘, x    x.append(10)    print ‘Chanaged local x to‘,xx = range(6)func_local(x)print ‘x is‘, x

def func_local(x):    print ‘x is‘, x    x.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‘, x    x.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‘, x    x.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‘, x    x[‘x‘] = 2    print ‘Chanaged local x to‘,xx = dict([(‘x‘,1), (‘y‘, 2)])func_local(x)print ‘x is‘, x

def func_local(x):    print ‘x is‘, x    x[‘x‘] = 2    print ‘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‘, x    x = (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‘, x    x = (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

 

python-global全域變數