Exception optimization

[GoogleCodeExporter]

So upon investigating a new plugin that has to traverse a *lot* of registry 
keys.  In so doing, it calls is_valid_address often which calls 
HiveAddressSpace vtop, which calls the following:

self.hive.Storage[ci_type].Map.Directory[ci_table].Table[ci_block].BlockAddress

Every time these ctypes try an attribute lookup, they pass through two 
exception handlers that are both expected to fail.  Unfortunately when an 
exception is caught, it's a bit costly (very minor hit if it doesn't get 
caught):

$ python -m 'timeit' -s 'd=dict(zip(range(1000), range(1000)))' $'try: 
d[1999]\nexcept KeyError: pass'
1000000 loops, best of 3: 2.73 usec per loop

$ python -m 'timeit' -s 'd=dict(zip(range(1000), range(1000)))' $'1999 in d and 
d[1999]'
10000000 loops, best of 3: 0.151 usec per loop

As such we should be trying to avoid doing try/catches that we expect to catch 
an exception.  I've attached an initial patch that uses __getattr__ instead of 
__getattribute__ (and therefore will only get called after that standard 
attribute check has failed).  Unfortunately I can't figure out what some of the 
code's for (checking "_" + attr?) and whether there will be unusual side 
effects, so a review and/or discussion about the changes would be much 
appreciated...  5:)

Original issue reported on code.google.com by mike.auty@gmail.com on 27 Apr 2011 at 6:02

Attachments:

• vol-exception-optimizing.patch

[GoogleCodeExporter]

Predominantly fixed by r1297.

Original comment by mike.auty@gmail.com on 23 Jan 2012 at 2:45

• Changed state: Fixed