== 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).
----
{{{
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 [http://www.mail-archive.com/web2py@googlegroups.com/msg06267.html 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/

----
DeveloperGuidelines