Simple Map Algebra Looped Through Rasters in a Directory

Discussion created by dcazar on Feb 17, 2013
Latest reply on Sep 12, 2013 by dcazar
I think I must be missing something pretty basic here because this isn't a complex operation. That said, I've always had difficulty with Map Algebra in scripts. I'd like to apply a constant multiplier to all of the rasters in a directory. They are in . tif format. When I run the separately in Python I get this error: 

Traceback (most recent call last):
  File "C:\Users\Derek\Desktop\multiply rasters.py", line 15, in <module>
    for raster_image in raster_list:
TypeError: 'NoneType' object is not iterable

When I run in it piecemeal in the Python window I get this error:

Runtime error
Traceback (most recent call last):
  File "<string>", line 1, in <module>
TypeError: can't multiply sequence by non-int of type 'float'

I don't think that the raster is being recognized as an input during the multiplication. I also don't know what else to try. Here is the code:

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


input_folder = r'C:\Users\Derek\Desktop\ToJordan\ToJordan\landsat'
arcpy.env.worspace = input_folder

#Set reflectance constant
const = 0.0001

# Get raster list, loop through and multiply be constant
raster_list = arcpy.ListRasters()
for raster_image in raster_list:
      print raster_image
      rast_mult = Raster(raster_image) * const
      raster_mult_out = input_folder + os.sep + raster_image + "_reflect.img"
      print raster_image + " Finished"

I hope someone can help.  Thanks!