Python Decorator: Contextlib

Context:

Start information

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Intermediate output Information

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End Message

Contextual Environment 1:

#!/usr/bin/python# -*- coding: utf-8 -*-class query (object):     Def __init__ (self, name):         self.name = name     def __enter__ (self):         print (' Begin ' )         return self    def __exit__ ( Self, exc_type, exc_value, traceback):        if  Exc_type:            print (' Error ')          else:             print (' End ')     def query (self):         print (' query info about %s ... '  % self.name)          with query(' Bob ')  as q:    q.query ()         query ( ' Bob '). Query ()

run Result:

Beginquery info about Bob ... Endquery info about Bob ...

Context 2: @contextmanager

From contextlib import contextmanagerclass query (object):    def  __init__ (Self, name):        self.name = name     def query (self):         print (' Query info  about %s '  % self.name) @contextmanagerdef  create_query (name):     print (' Begin ')     q = query (name)     yield q     print (' End ')     with create_query (' Bob ')  as q:     q.query ()

Operation Result:

Beginquery info about Bob ... End

Context 3: @contextmanager simplify again

From contextlib import contextmanager@contextmanagerdef tag (name): Print ("<%s>"% name) yield print ("</% S> "% name" with tag ("H1"): Print ("Hello") Print ("World")

The result of the above code execution is:

No context: @closing use closing () to turn the object into a context object, for example, using Urlopen () with a with statement:
from contextlib import closingfrom urllib.request import urlopenwith  Closing (Urlopen (' https://www.baidu.com '))  as page:    for line in  page:        print (line) 
B ' 

Don't know how to verify the closing
from contextlib import contextmanager@contextmanagerdef closing (thing):     try:        yield thing    finally:         thing.close () 
The result of the above code execution is:


Python Decorator: Contextlib