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Date: Fri, 26 Jun 2015 18:44:42 +0100
From: MRAB <python@mrabarnett.plus.com>
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Subject: Re: how to replace some methods with instrumented ones
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On 2015-06-26 18:12, georgeryoung@gmail.com wrote:
> [python 2.7, linux]
> I have a python app. I cannot modify the file.  But I can import it and mess with it.  I need to perform brief tasks before and after some of the member functions.
> I'd like to do this in as clear and maintainable way as possible (no third party imports).  Here's what I have now(which works):
>
> from newvbr import *  #get all the stuff from the newvbr app.
>
> def perf_time(tag):  # I do a little more than this, but you get the idea.
>      print >>sys.stderr, datetime.datetime.now().isoformat() + tag
>
> def perf(tag):
>      def decorator(fn):
>        a  def wrapper(*args):
>              perf_time('start %s' % tag)
>              ret = fn(*args)
>              perf_time('end %s' % tag)
>              return ret
>          return wrapper
>      return decorator
>
>
> I use this on various members of various classes in the newvbr app:
>
> old_database_snapshot = VerticaSession.database_snapshot
> @perf('db_snap')
> def new_database_snapshot(self, name):
>      old_database_snapshot(self, name)
> VerticaSession.database_snapshot = new_database_snapshot
>
> old_object_snapshot = VerticaSession.object_snapshot
> @perf('obj_snap')
> def new_object_snapshot(self, name):
>      old_object_snapshot(self, name)
> VerticaSession.object_snapshot = new_object_snapshot
>
> main()  #do the usual stuff of the imported app, but with annotations.
>
>
> This is still pretty laborious.  How can I make something roughly like:
>
>     super_tagger(VerticaSession.database_snapshot)
>
> that does all the above?  I need to tag a bunch of function members like this.  I don't insist on using decorators, it just looked like that kind of problem.
>
You could do something like this:

def super_tagger(module, function_name, tag):
     original_function = getattr(module, function_name)

     @perf(tag)
     def wrapper(*args, **kwargs):
         return original_function(*args, **kwargs)

     setattr(module, function_name, wrapper)

and then:

super_tagger(VerticaSession, 'database_snapshot', 'db'snap')


It might be cleaner to merge the functionality of 'perf' into it:

def super_tagger(module, function_name, tag):
     original_function = getattr(module, function_name)

     def wrapper(*args, **kwargs):
         perf_time('start %s' % tag)
         result = original_function(*args, **kwargs)
         perf_time('end %s' % tag)
         return result

     setattr(module, function_name, wrapper)