python with statement 进行文件操作指南

set thing up
try：
  do something
except :
  handle exception
finally:
  tear thing down

#!/usr/bin/env python 
from __future__ import with_statement  
filename = 'for_test.txt' 
def output(content): 
  print content 
#functio solution 
def controlled_execution(func): 
  #prepare thing 
  f = None 
  try: 
    #set thing up 
    f = open(filename, 'r') 
    content = f.read() 
    if not callable(func): 
      return 
    #deal with thing  
    func(content) 
  except IOError, e: 
    print 'Error %s' % str(e) 
  finally: 
    if f:  
      #tear thing down 
      f.close() 
def test(): 
  controlled_execution(output) 
test() 

#yield solution 
def controlled_execution(): 
  f = None 
  try: 
    f = open(filename, 'r') 
    thing = f.read() 
    #for thing in f: 
    yield thing 
  except IOError,e: 
    print 'Error %s' % str(e) 
  finally: 
    if f:  
      f.close() 
def test2(): 
  for content in controlled_execution(): 
    output(content) 

#class solution 
class controlled_execution(object): 
  def __init__(self): 
    self.f = None 
  def __enter__(self): 
    try: 
      f = open(filename, 'r') 
      content = f.read() 
      return content 
    except IOError ,e: 
      print 'Error %s' % str(e) 
      #return None 
  def __exit__(self, type, value, traceback): 
    if self.f: 
      print 'type:%s, value:%s, traceback:%s' % \ 
          (str(type), str(value), str(traceback)) 
      self.f.close() 
def test3(): 
  with controlled_execution() as thing: 
    if thing: 
      output(thing) 
 

def test4(): 
  with open(filename, 'r') as f: 
    output(f.read()) 
 
  print f.read()