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April 2010

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Re: decorators only when __debug__ == True
by LX April 1, 2010

April 1, 2010

On Mar 30, 2:41 pm, MRAB <pyt...(a)mrabarnett.plus.com> wrote: > LX wrote: > > On Mar 29, 6:34 pm, MRAB <pyt...(a)mrabarnett.plus.com> wrote: > >> LX wrote: > >>> Hi all, I have a question about decorators. I would like to use them > >>> for argument checking, and pre/post conditions. However, I don't want > >>> the additional overhead when I run in non-debug mode. I could do > >>> something like this, using a simple trace example. > >>> @decorator > >>> def pass_decorator(f, *args, **kw): # what about the slow-down that > >>> incurs when using pass_decorator? > >>> return f(*args, **kw) > >>> @decorator > >>> def trace_decorator(f, *args, **kw): > >>> print "calling %s with args %s, %s" % (f.func_name, args, kw) > >>> return f(*args, **kw) > >>> trace_enable_flag = False #__debug__ > >>> trace = trace_decorator if trace_enable_flag else pass_decorator > >>> Trouble is, there is still an additional encapsulating function call. > >>> Is there any way to eliminate the extra function call altogether? > >>> Thanks in advance! > >> I think you have misunderstood certain details about decorators. > > >> This code with adecorator: > > >> @decorator > >> def hello(): > >> print "hello world" > > >> basically does this: > > >> def hello(): > >> print "hello world" > >> hello =decorator(hello) > > >> so your non-decoratorjust needs to return the function it was passed: > > >> def pass_decorator(func): > >> return func > > >> and your tracedecoratorwould be something like this: > > >> def trace_decorator(func): > >> def show(*args, **kwargs): > >> print "calling %s with args %s, %s" % (func.func_name, > >> args, kwargs) > >> result = func(*args, **kwargs) > >> print "returning %s from %s" % (result, func.func_name) > >> return result > >> return show > > > Sure, but during runtime, pass_decorator will still be called, even > > though it doesn't do anything. I am wondering if I can disable this > > additional function call at non-debug runtime. In other words, I want > > the calling stack to contain nodecoratorat all, not even > > pass_decorator. > > > I should mention that, in my code, the symbol "decorator" is imported > > from Michele Simionato'sdecorator.py file. > > pass_decorator will be called when the decorated function is _defined_, > but not when the decorated function is _called_. Why is it then that during runtime, with a breakpoint in some arbitrary main() in main.py, I get something similar to the following call stack: main.py, line xxx, in <module> main() <string>, line 2, in main decorator.py, line 261, in pass_decorator return f(*args, **kw) main.py, line yyy, in main() * breakpoint line here * It looks to me the call stack still includes the additional level of the decorator... what am I missing? Thank you for your time.

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