Loop raster dataset in Python

Hi,
I am very new to Python and I want to extract raster by mask for a number of images. I am attempting to write python code for this and incorporate a loop so it will process every raster image within the folder without me manually changing it. This is my code below but it does not work. From the #Loop through list of rasters sections i.e. rasters.reset() all the errors begin to occur. Can someone please help me fix this coding.


# Import system modules
import arcpy
from arcpy import env
from arcpy.sa import *

# Set environment settings
env.workspace = "J:\PhD\Vegetation\MODIS13Q1\MODIS_NDVI_z56"

# Set local variables
inRaster = "J:\MODIS"
inMaskData = "arcreproarea.shp"
outRaster = "J:\\MODIS"

# Check out the ArcGIS Spatial Analyst extension license
arcpy.CheckOutExtension("Spatial")

# Get a list of the rasters in the workspace
rasters = arcpy.ListRasters()
rasters

# Loop through the list of rasters
rasters.reset()
raster = rasters.next()

while raster:
# Set the outputname for each output to be the same as the input
output = out_workspace + raster


# Process: Extract by Mask
arcpy.gp.ExtractByMask_sa(inRaster, inMaskData, outRaster)


# Loop
raster = rasters.next()


Thanks,
Jess