python-global全局變量
阿新 • • 發佈：2017-12-06
spa tps pen 函數 image src b- lis 完成
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，即變量名稱對於函數來說是局部的，這稱為變量的作用域，示例如下：
def func_local(x):
print ‘x is‘, x
x = 2
print ‘Chanaged local x to‘,x
x = 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 y
print ‘y is‘, y
y = 50
print ‘Changed local y to‘, y
y = 10
func_global()
print ‘Value of y is‘, y
def func_global():
global y
print ‘y is‘, y
y = 50
print ‘Changed local y to‘, y
y = 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‘, x
x.append(10)
print ‘Chanaged local x to‘,x
x = 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‘,x
x = 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‘,x
x = 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‘,x
x = 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‘,x
x = 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‘,x
x = 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‘,x
x = (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‘,x
x = (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全局變量