How to determine whether Raster statistics have been calculated

Question

Hi

I have a script which fails when I use the GetRasterProperties_management function on a dataset where statistics have not yet been calculated.

How can I in a simple way check whether the statistics have been calculated ?

There is strangely enough not a Raster set attribute named "hasStatistics" or similar to get from Describe fuunction 
neither does the GetRasterProperties simply rerturn a Null object 
so I could use something like :

if arcpy.GetRasterProperties_management (outRaster, "MINIMUM") == None:
               CalculateStatistics_management (outRaster)

All help is most welcome

Michael

JakeSkinner · Answer

I just wanted to note that an aux.xml can exist when statistics do not.  For example, the aux.xml will also be used as a pointer to the pyramid file.  This is explained here:

http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//009t00000027000000.htm

You may want to go along the lines Niklas mentioned.  Ex:try:
    arcpy.GetRasterProperties_management(input, "STD")
    print "Statistics exist"
except arcpy.ExecuteError:
    arcpy.CalculateStatistics_management(input)
    print "Statistics were calculated"

NiklasNorrthon · Answer

Another way to solve the problem is to just assume that statistics is there and deal with the problem when it isn't.
# Pseudocode:
while True:
    try: 
        arcpy.FunctionThatNeedsRasterStatistics(raster)
        break
    except arcpy.ExecuteError:
        arcpy.CalculateStatistics(raster)

This pattern also has the advantage that it isn't subject to race conditions (not that those are likely for raster statistics, but in other contexts that can be a real issue.

MichaelStjernholm · Answer

Thanks Hongmei for reminding me of using the test of whether the aux.xml file exists - I use similar approach in other calculations.

regards michael