python的作用域

局部作用域中不应对全局变量进行赋值

   #!/usr/bin/python
   #coding:utf-8
   
   def printNum():
       print "num : %d" % num#可以读取全局变量
       
      
  num = 10
  
  if __name__ == "__main__":
      print "num is: %d" % num
      printNum()
  else:
      print "not in main..."

   #!/usr/bin/python
   #coding:utf-8
   
   def printNum():
       num += 5#给全局变量赋值错误
       print "num : %d" % num
       
      
  num = 10
  
  if __name__ == "__main__":
      print "num is: %d" % num
      printNum()
  else:
      print "not in main..."

局部作用域中使用 global实现对全局变量进行赋值

#!/usr/bin/python
#coding:utf-8
   
   def printNum():
       global num#如果需要给全局变量赋值，加上global
       num += 5
       print "num : %d" % num
       
      
  num = 10
  
  if __name__ == "__main__":
      print "num is: %d" % num
      printNum()
  else:
      print "not in main..."

局部作用域中全局变量应是只读是不准确的

 #!/usr/bin/python
 #coding:utf-8
 
 def printNum():
     global num
     num += 5
     print "num : %d" % num
     
 def printArray():
     ary.append("hello")#可以改变全局变量
     
     global ary#如果直接赋值的话会出错，所以需要加上global
     ary = ["new array"]
     print ary
     
 num = 10
 ary = ["one"]
 
 if __name__ == "__main__":
     print "num is: %d" % num
     print "array is :",ary
     printNum()
     printArray()
 else:
     print "not in main..."

全局作用域指的是本模块而不是程序 

python的作用域,布布扣,bubuko.com

python的作用域

原文：http://blog.csdn.net/iitvip/article/details/19974439