title: Looping through Raster to compute Mean in Cell Statistics
body: <p>I am attempting to loop through a set of MODIS data to compute averages by period. Since 2000 is missing periods 1 - 3 I am just computing the averages of periods 1 -3 for 2001 through 2012. I am then computing the averages for periods 4 - 23 with data from 2000 through 2012. I have written a script to do this, but keep getting an error 000732 about my data not existing or not being supported. I opened one of the grids in Arc and it was fine. I am not sure why I am getting this error and have included the code below.  I have tried multiple ways to feed the rasters in, but get the same error.</p>
  
  <pre><code># Import system modules
  import arcpy
  from arcpy import env
  from arcpy.sa import *
  
  # Set environment settings
  env.workspace = "S:\\MODIS\\DATA_v05\\modis016_0250_ndvi\\us\\"
  
  # Check out any necessary licenses
  arcpy.CheckOutExtension("spatial")
  
  # Path names for input and output data
  path = "S:\\MODIS\\DATA_v05\\modis016_0250_ndvi\\us\\or"
  output_path = "B:\\MODIS_NDVI\\Avg_per_period\\avg"
  
  for period in range (1,3):
  #MODIS does not have data for the first three periods of 2000.  This will calculate an                                                                 average for the first three periods ignoring the year 2000.  It will also place a 0 in front of the single digit to match the file name.
  if period &lt;= 3:
      period = ("0"+str(period))
      grids01 = Raster('"' + path + "01" + period + "ndvius" + '"')
      grids02 = Raster('"' + path + "02" + period + "ndvius" + '"')
      grids03 = Raster('"' + path + "03" + period + "ndvius" + '"')
      grids04 = Raster('"' + path + "04" + period + "ndvius" + '"')
      grids05 = Raster('"' + path + "05" + period + "ndvius" + '"')
      grids06 = Raster('"' + path + "06" + period + "ndvius" + '"')
      grids07 = Raster('"' + path + "07" + period + "ndvius" + '"')
      grids08 = Raster('"' + path + "08" + period + "ndvius" + '"')
      grids09 = Raster('"' + path + "09" + period + "ndvius" + '"')
      grids10 = Raster('"' + path + "10" + period + "ndvius" + '"')
      grids11 = Raster('"' + path + "11" + period + "ndvius" + '"')
      grids12 = Raster('"' + path + "12" + period + "ndvius" + '"')
      #grids = grids01 + ";" + grids02 + ";" + grids03 + ";" + grids04 + ";" + grids05 + ";" + grids06 + ";" + grids07 + ";" + grids08 + ";" + grids09 + ";" + grids10 + ";" + grids11 + ";" + grids12   
      avg_temp = ('"' + output_path + period + "temp" + '"')
      avg = (output_path + period)
      outCellStatistics = CellStatistics([grids01, grids02, grids03, grids04, grids05, grids06, grids07, grids08, grids09, grids10, grids11, grids12], "MEAN", "DATA")
      outCellStatistics.save(avg_temp)
  #This is will place a 0 in front of the single digit to match the file name.
  elif period &lt; 10:
      period = ("0"+str(period))
      grids00 = ('"' + path + "00" + period + "ndvius" + '"')
      grids01 = ('"' + path + "01" + period + "ndvius" + '"')
      grids02 = ('"' + path + "02" + period + "ndvius" + '"')
      grids03 = ('"' + path + "03" + period + "ndvius" + '"')
      grids04 = ('"' + path + "04" + period + "ndvius" + '"')
      grids05 = ('"' + path + "05" + period + "ndvius" + '"')
      grids06 = ('"' + path + "06" + period + "ndvius" + '"')
      grids07 = ('"' + path + "07" + period + "ndvius" + '"')
      grids08 = ('"' + path + "08" + period + "ndvius" + '"')
      grids09 = ('"' + path + "09" + period + "ndvius" + '"')
      grids10 = ('"' + path + "10" + period + "ndvius" + '"')
      grids11 = ('"' + path + "11" + period + "ndvius" + '"')
      grids12 = ('"' + path + "12" + period + "ndvius" + '"')
      grids = "[" + grids00 + "," + grids01 + "," + grids02 + "," + grids03 + "," + grids04 + "," + grids05 + "," + grids06 + "," + grids07 + "," + grids08 + "," + grids09 + "," + grids10 + "," + grids11 + "," + grids12 + "]"    
      avg_temp = (output_path + period + "temp")
      avg = (output_path + period)
      arcpy.gp.CellStatistics_sa(grids,avg_temp,"MEAN", "DATA")
   #These are double digit periods and will match the file name without correction.
  else:
      period = (str(period))
      grids00 = ('"' + path + "00" + period + "ndvius" + '"')
      grids01 = ('"' + path + "01" + period + "ndvius" + '"')
      grids02 = ('"' + path + "02" + period + "ndvius" + '"')
      grids03 = ('"' + path + "03" + period + "ndvius" + '"')
      grids04 = ('"' + path + "04" + period + "ndvius" + '"')
      grids05 = ('"' + path + "05" + period + "ndvius" + '"')
      grids06 = ('"' + path + "06" + period + "ndvius" + '"')
      grids07 = ('"' + path + "07" + period + "ndvius" + '"')
      grids08 = ('"' + path + "08" + period + "ndvius" + '"')
      grids09 = ('"' + path + "09" + period + "ndvius" + '"')
      grids10 = ('"' + path + "10" + period + "ndvius" + '"')
      grids11 = ('"' + path + "11" + period + "ndvius" + '"')
      grids12 = ('"' + path + "12" + period + "ndvius" + '"')
      grids = "[" + grids00 + "," + grids01 + "," + grids02 + "," + grids03 + "," + grids04 + "," + grids05 + "," + grids06 + "," + grids07 + "," + grids08 + "," + grids09 + "," + grids10 + "," + grids11 + "," + grids12 + "]" 
      avg_temp = (output_path + period + "temp")
      avg = (output_path + period)
      arcpy.gp.CellStatistics_sa(grids,avg_temp,"MEAN", "DATA")
  </code></pre>