Python变量作用域范围

关键词： python;作用域; Variable Scope;

1、Python中能够改变变量作用域的代码段是def、class、lamda三类。
代码块：if/elif/else、try/except/finally、for/while 等不更改变量的作用域，在其作用范围之外，仍然能够访问到变量。
2、Python变量搜索顺序是局部变量---上层变量---全局变量。

变量作用域

代码示例：

def scopetest():
    localvar=6;
    print(localvar)  
scopetest()
#print(localvar) #去除注释这里会报错，因为localvar是本地变量
while True:  
    newvar=8  
    print(newvar)  
    break;    
print(newvar)    
try:  
    newlocal=7  
    raise Exception  
except:  
    print(newlocal) #代码块外可以访问

Out:
6
8
8
7

number = 5
def func0():
    #It's OK to reference.
    print number

def func1():
    #new local variable.
    number = 10
    print number

def func2():
    #global declaration.
    global number
    print number
    number = 10
    print number

print "Before calling any function, number is {}".format(number)
print "Calling func0()----------"
func0()
print "Calling func1()----------"
func1()
print "After calling func1(), number is {}".format(number)
print "Calling func2()----------"
func2()
print "After calling func2(), number is {}".format(number)

Out:
Before calling any function, number is 5
Calling func0()----------
5
Calling func1()----------
10
After calling func1(), number is 5
Calling func2()----------
5
10
After calling func2(), number is 10

变量搜索顺序：

def scopetest():  
    var=6;  
    print(var)
    def innerFunc():  
        print(var)  #look here  
    innerFunc()        
var=5   
print(var)  
scopetest()  
print(var)  

Out: 
5
6
6
5

根据调用顺序反向搜索，先本地变量再全局变量，例如搜先在innerFunc中搜索本地变量，没有，向上一级scopetest，发现本地变量var=6，输出。

参考：
Python Variable Scope
Python 变量作用域