None of the following methods turn of the .xml history logging (for me, stored under C:\Users\csny490\AppData\Roaming\ESRI\Desktop10.0\ArcToolbox\History):
arcpy.loghistory = False
arcpy.logHistory = False
arcpy.env.loghistory = False
arcpy.env.logHistory = False
arcpy.setLogHistory = False
arcpy.SetLogHistory = False
arcpy.env.setLogHistory = False
arcpy.env.SetLogHistory = False
Curiously, you can also seem to set any method you think up. For example:
>>> arcpy.whyDoesntThisWork = False
>>> print arcpy.whyDoesntThisWork
False
Which gives the false sense that some of these settings are "working" when in fact they are invalid methods and aren't actually serving any purpose.
Could it be that the history log setting in v10 via arcpy is just a placebo now and there is no way to tun it off? Seems that tuning it off via ArcMap (ArcMap > Geoprocessing > Geoprocessing Options) only turns off the logging when the tool is run via ArcMap. I would like to turn this setting off for all my scripts, but seemingly can't do that anymore in v10 arcpy... Yargh!
Note that:
import arcgisscripting
gp = arcgisscripting.create(9.3)
gp.loghistory = False
still works to stop history logging in v10.0.
In my experience with the old logging system (that use .tbx files), the larger the history file becomes the slower the tools execute. Seems that in v10 (9.3 too I think) the .xml files are created anew ever hour, but regardless, it is still possible to issue thousands of tool commands in an hour - each tool execution making the hourly .xml file larger, and the entire history fiolder larger as well.
Please ESRI: We need a way to turn the geoprocessing history log off via arcpy!