Applying Map Algebra to List of Rasters and Saving New File in New Directory?

Question

I am trying to multiply each raster by coefficient using Map Algebra in Python. I receive the following error for the code below:

calcRaster.save(calcRasterName) AttributeError: 'unicode' object has no attribute 'save'

import arcpy
from arcpy import env
from arcpy.sa import *

env.workspace = r"C:\SomeFolder"
outFolder = r"C:\SomeFolder"

arcpy.CheckOutExtension("Spatial")

rasters = arcpy.ListRasters()
for inRaster in rasters:
    calcRaster = inRaster * 720
    calcRasterName = outFolder + "/" + calcRaster
    calcRaster.save(calcRasterName)

Based on some searching, I redefined the calcRaster variable to:

  calcRaster = (Raster(inRaster) * 720)

However, I receive some comments and a new error:

File "C:\Users\rrotz\Desktop\Pycharm\RasterCalculator.py", line 13, in calcRasterName = outFolder + "/" + calcRaster

File "C:\Program Files (x86)\ArcGIS\Desktop10.5\ArcPy\arcpy\sa\Functions.py", line 4329, in Plus in_raster_or_constant2)

File "C:\Program Files (x86)\ArcGIS\Desktop10.5\ArcPy\arcpy\sa\Utils.py", line 53, in swapper result = wrapper(*args, **kwargs)

File "C:\Program Files (x86)\ArcGIS\Desktop10.5\ArcPy\arcpy\sa\Functions.py", line 4326, in Wrapper ["Plus", in_raster_or_constant1, in_raster_or_constant2])

RuntimeError: ERROR 000732: Input Raster: Dataset S:\Group Projects\HDF5\2 Tiff Data\8 Monthly Scaled/ does not exist or is not supported

The last RunTimeError is regarding the outfolder path that I designated for the final calculated rasters.

Answer 1

calcRaster is a temporary raster, not a text string. You will need to find another way of naming your result, like outRasterName = '{}720'.format(inRaster).

Python has tools for creating complete path names from path fragments (folder & file names) use os.path.join like this: CalcRasterName = os.path.join(outFolder, outRasterName).

Answer 2

I was able to get the code working using the following approach.

import arcpy,os,sys,string
from arcpy import env
from arcpy.sa import *

arcpy.CheckOutExtension("Spatial")

input_folder = r'SomeFolder'
arcpy.env.workspace = input_folder
output_folder = r'SomeFolder'

#Set reflectance constant
const = 672

# Get raster list, loop through and multiply be constant
raster_list = arcpy.ListRasters()
for inRaster in raster_list:
      print inRaster
      rast_mult = Raster(inRaster) * const 
      raster_mult_out = output_folder + os.sep + inRaster + ".tif"
      rast_mult.save(raster_mult_out)

I'll post another version as advised above shortly. Thanks all!