Iterate many raster and many shapefiles in python using the zonal statisitics as table tool

Question

I am pretty new to coding.

I have to execute zonal statistics on many shapefiles (~20) for many rasters (~300). Essentially, the first shapefile is used to process all zonal statistics for all rasters and merge it to one table. This is then repeated for the second shapefile and so on. The code also creates two new fields (year and date) and populates them from the raster name. The rasters are .tif file formats.

I keep running into error 000865: Parameters are not valid. Input value raster does not exist. Failed to execute (ZonalStatisticsAsTable).

My code so far looks like:

# Import system modules
import arcpy, sys, os, string, glob
print "imported modules"

# Check out licenses
arcpy.CheckOutExtension("spatial")
# Overwrite 
arcpy.env.overwriteOutput = True

def zonal_SWE(rasters, shapes):
    arcpy.env.workspace = rasters
    rasterlist = arcpy.ListRasters()
    arcpy.env.workspace = shapes
    shplist = arcpy.ListFeatureClasses()
    for raster in rasterlist:
        for i in shplist:
            out_tbl = tbl + "\\" + raster + "_ZStats"
            print 'Zonal Statistics based on SWE : ' + raster[9:13]
            # Preform zonal statistics on the polygon file within the variable 'znlyr'
            z = arcpy.gp.ZonalStatisticsAsTable_sa(i, InZnValFld, raster, out_tbl, "DATA", "MIN_MAX_MEAN")
            # Create a new field to add the filename information
            arcpy.AddField_management(z, fieldname1, "DOUBLE")
            # Create a new field to add the filename information
            arcpy.AddField_management(z, fieldname2, "DOUBLE")
            # Add the Year value from the filename to the new field
            arcpy.CalculateField_management(z, fieldname1,raster[9:13])
            # Add the Month value from the filename to the new field
            arcpy.CalculateField_management(z, fieldname2,raster[13:15])
            arcpy.Append_management(z, Template, "","","")

#----------------variables--------------
znshp = r"C:\Users\Documents\Projects\shapefile_folder"
grd = r"C:\Users\Documents\Projects\raster_folder"
tbl = r"C:\Users\Documents\Projects\Table_folder"
InZnValFld = "OBJECTID"
fieldname1= "Year"
fieldname2= "Month"
Template = r"C:\Users\Documents\Projects\Tables\Template.dbf"

#---------------------------------------
print "starting zonal SWE"
zonal_SWE(grd, znshp)
print "done"

Answer 1

Your code is flawed, you get the list of rasters by setting then workspace, you then get the list of shapefiles by resetting the workspace to znshp. You then reference each raster in rasterlist. This list will hold just the name and not the full path. The ZonalStatisticsAsTable tool honours workspace but as you have pointed that to where the shapefiles are it's not surprising it cannot find the rasters!

I would recommend constructing the full path to the raster by concatenating rasters with raster and that will be a correct input parameter for the tool.