在函数内部定义变量时,他们与函数外部具有相同名称的其他变量没有任何关系,即变量名称对于函数来说是局部的,这称为变量的作用域,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
执行结果:
x is 50 Chanaged local x to 2 x is still 50
如果想在函数内部改变函数外的变量值,用global语句完成
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
执行结果:
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
函数参数若是list、set、dict可变参数,在函数内改变参数,会导致该参数发生变化,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
执行结果
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
执行结果:
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
执行结果:
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
执行结果
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)
若传入可变参数如list、set、dict,在函数内部对参数做出修改,参数本身发生变化,tuple、str不变