2017 - Albert Sweigart - Logging and Testing

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LOGGING AND TESTING AND DEBUGGING, OH MY! @AlSweigart [email protected] (last name rhymes with “why dirt”) bit.ly/ohmypy

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Why?

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LOGGING

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LIVE DEMO!

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This is terrible.

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TERRIBLE Print Debugging

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Why do logging instead of print? • Debug output vs. normal output • Easier to remove debug messages. • Easier to put debug messages back. • Fine grain control with logging levels.

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Logging import logging logging.basicConfig( level=logging.DEBUG) logging.debug('The log message.') logging.disable(logging.CRITICAL) Back to the live demo… This is looks complicated.

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Logging Levels • DEBUG • INFO • WARN • ERROR • CRITICAL • logging.basicConfig( level=logging.DEBUG) • logging.disable(logging.CRITICAL)

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DEBUG • Low-level debugging information. • Variables values, etc. • You only look at when something has gone wrong. • Probably going to ignore this.

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INFO • Report that a perfectly ordinary event happened.

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WARN

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ERROR CC BY-SA https://www.flickr.com/photos/74157931@N00/

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CRITICAL

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Logging Levels • logging.debug('message') • logging.info('message') • logging.warn('message') • logging.error('message') • logging.critical('message') • logging.basicConfig( level=logging.DEBUG) • logging.disable(logging.CRITICAL)

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Logging to Screen and File logging.basicConfig( level=logging.DEBUG) logging.basicConfig( filename='logfile.txt', level=logging.DEBUG)

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Following log files in real time tail –f (On Windows, install Cygwin.) Back to the live demo…

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DEBUGGING

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import pdb; pdb.set_trace() Back to the live demo…

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Where am I? l . (List) w (Where)

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Print Values p

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Stepping s (Step Into) n (Next / step over) r (Return / step out) c (continue running until next breakpoint)

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Breakpoints • b (list all breakpoints & their numbers) • b • b • cl (clear bp) • import pdb; pdb.set_trace()

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Quit the debugger q

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import pdb; pdb.set_trace()

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TESTING

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import doctest doctest.testmod() Back to the live demo…

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• Doctests are not a replacement for unit tests. • Doctests are unit tests for documentation. • Back to the live demo…

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if __name__ == '__main__': import doctest doctest.testmod()

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Logging import logging logging.basicConfig( level=logging.DEBUG) logging.debug('The log message.') logging.disable(logging.CRITICAL)

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Debugging import pdb; pdb.set_trace()

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Testing import doctest doctest.testmod()

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LOGGING AND TESTING AND DEBUGGING, OH MY! @AlSweigart [email protected] (last name rhymes with “why dirt”) bit.ly/ohmypy