Optimisation

Writing code which runs fast.

Consider having configurations which are read from DB frequently but written-to rarely, be set in configuration files which are written-out from the DB (like the CSS from themes)

• ​http://wiki.python.org/moin/PythonSpeed/PerformanceTips
• ​http://www.python.org/doc/essays/list2str/
• ​http://www.skymind.com/~ocrow/python_string/
• ​http://diveintopython.org/performance_tuning/index.html
• If a specific inner-loop routine canot be optimised in Python, then consider writing a C routine for this use case.

Specific Examples

NB These vary on cases, so use the Profiler to see how they work in your cases...

for i in range(0, len(rows)):
     row = rows[i]

runs much faster than:

 for row in rows:

(0.05 vs. 0.001 seconds in one test case, 2x improvement in another & a slight negative improvement in a 3rd).

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value = db(table.id==id).select(table.field, limitby=(0, 1))[0]

runs 1.5x faster than:

value = table[id].field

(0.012 vs. 0.007 seconds vs in a test case)

Profiling

• Web2Py can ​use cProfile:
  • web2py.py -F profiler.log
  • or if running as service, edit options.py: profiler_filename = 'profiler.log'
• ​http://docs.python.org/library/profile.html
• ​http://www.cherrypy.org/wiki/Testing#Profiling
• ​http://mg.pov.lt/profilehooks/
• YSlow plugin for Firebug: ​http://developer.yahoo.com/yslow/

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DeveloperGuidelines