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[Python-ideas] Efficient debug logging

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Can you wrap the expensive functions in lambdas? And have your loggerevaluate it, only if required?> debugLog( ‘info is %r’ % (lambda: expensiveFunction(),) )On 2017-02-14 10:51, Barry Scott wrote:> 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>> _______________________________________________> Python-ideas mailing list>Python-ideas at python.org>https://mail.python.org/mailman/listinfo/python-ideas> Code of Conduct:http://python.org/psf/codeofconduct/

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