python----with

python的with ---as 的用法 

with EXPRESSION [ as VARIABLE] :

      WITH-BLOCK

这个语法是用例代替传统的try .... finally语法的

file = open("/tmp/foo.txt")

try:

         data = file.read()

finally:

           file.close()

使用with...as...的方式替换

with open("/tmp/foo.txt") as file:

data = file.read()