Convert a folder with raster files to slope files

rasterToSlope.py

import arcpy  
arcpy.CheckOutExtension("Spatial")  
from arcpy import env
from arcpy.sa import *  
import os

maindir = r'G:\RasterFolder'
files = [x for x in os.listdir(maindir) if x.endswith(".tiff")]
outFolder = os.path.join(maindir, 'slope')

if not os.path.exists(outFolder):
    os.makedirs(outFolder)

for file in files:
	filepath = os.path.join(maindir, file)
	#elevMINResult = arcpy.GetRasterProperties_management(filepath, "MINIMUM")  
	#elevMin = float(elevMINResult.getOutput(0))  
	#print(elevMin)
	#outMinus = Minus(filepath, elevMin) 

	# note the specification of a dataset name in the gdb below
	filename = str(file)[:-4] + 'tif'
	outSlope = Slope(filepath)

	outname = os.path.join(outFolder, filename)	
	print(outname)
	#logRaster = Log10(outMinus)
	outSlope.save(outname)