[Python-ideas] Efficient debug logging

[Victor Stinner]

Yeah, I had a similar issue in a previous company. A colleague wrote a
script using a regex to remove these debug logs in the .py code.

IHMO the clean design for that would be to support officially preprocessors
in Python. My PEP opens the gate for that:
https://www.python.org/dev/peps/pep-0511/

It would allow to write easily your own light preprocessor just to remove
debug logs.

Victor

Le 14 févr. 2017 5:24 PM, "Barry Scott" <barry at barrys-emacs.org> a écrit :

> A common pattern I use is to have logging calls for debug and information
> with my applications.
> The logging calls can be separately enabled and disabled.
>
> For example:
>
> debug_log_enabled = False
> def debugLog( msg ):
>       If debug_log_enabled:
>             print( ‘Debug: %s’ % (msg,) )
>
> Then the caller can simple write:
>
> def main():
>       debugLog( ‘Start of main’ )
>
> This is fine until the evaluation of the msg becomes expensive.
>
>         debugLog( ‘info is %r’ % (expensiveFunction(),) )
>
> What would be nice is to be able to avoid evaluation the tuple of
> arguments if debug is
> disabled as this can be expensive. I can write this:
>
>         if debug_log_enabled:  debugLog( ‘info is %r’ %
> (expensiveFunction(),) )
>
> But that is a more code then I would like to write. And if the debug code
> is a performance problem cannot
> be left in the production code.
>
> I could combine the boolean and the log function by using a class to tidy
> up the implementation.
>
> class DebugLog:
>         def __init__( self, enabled = False ):
>                 self.enabled = enabled
>
>         def __bool__( self ):
>                 return self.enabled
>
>         def __call__( self, msg ):
>                 if self.enabled: print( ‘Debug: %s’ % (msg,) )
>
> And call like this:
>
>         dbg_log = DebugLog()
>
>        If dbg_log: dbg_log( ‘a debug message’ )
>
> But I’d like to only write:
>
>         dbg_log( ‘a debug message’ )
>
> And have the evaluation of the argument skipped unless its dbg_log is
> enabled.
>
> I cannot see how to do this with python as it stands.
>
> Something would have to be added to allow python to short circuit the
> argument tuple evaluation.
>
> Maybe python can check for a special dunder on the class that know how to
> do this idiom, __if_true_call__?
>
> Thoughts?
>
> Barry
>
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