Using ArcPy ListRaster in Walk?

Question

I am trying to select all rasters using arcpy.ListRasters within all folders of a directory using arcpy.da.Walk. I'm using arcMap 10.2.

An example portion of the code I have:

workspace = ("...")
output = ("...")

walk = arcpy.da.Walk(workspace, topdown=True, datatype= "RasterDataset", type = "TIF")

for dirpath, dirnames, filenames in walk:
    for filename in filenames:
        rasters = arcpy.ListRasters("*", "TIF")
        print rasters

Doesn't work. It results in :

None
None
None
None
None
None
None
None
None

This works and lists all raster names, but what I need is a list of the raster that I'm able to use for further processing:

workspace = ("...")
output = ("...")

walk = arcpy.da.Walk(workspace, topdown=True, datatype= "RasterDataset", type = "TIF")

for dirpath, dirnames, filenames in walk:
    for filename in filenames:
        print filename

I'm trying to use ListRasters so that I can batch process those rasters. In most cases I could do something like:

import arcpy arcpy.env.workspace = (...)
rasters = arcpy.ListRasters("*", "TIF") 
for raster in rasters: arcpy.BatchBuildPyramids_management(raster) 

But in this case I have a lot of folders with rasters in each folder. I need to grab all those rasters into a raster list I can then batch process

Answer 1

You can use os.path.join() to combine dirpath and filename into a full file path. As @MichaelStimson points out, using ListRasters() in Walk is redundant. The Walk documentation provides more details. For example:

import arcpy, os

inws = r'X:\temp'
rasters = []

walk = arcpy.da.Walk(inws, topdown=True, datatype= "RasterDataset", type = "TIF")

for dirpath, dirnames, filenames in walk:
    for filename in filenames:
        rasters.append(os.path.join(dirpath, filename))

---

The output is a list of rasters including their directory path.

>>> rasters
[u'X:\\temp\\dir1\\file1.tif',
 u'X:\\temp\\dir1\\dir1a\\file1a.tif',
 u'X:\\temp\\dir2\\file2.tif',
 u'X:\\temp\\dir3\\file3.tif']
>>> 

---

As a side note, if you are using Python >=3.5, you can recursively walk directories using glob.iglob(), which is very easy to implement. For example, the following produces the same list of rasters as in the previous example:

import glob
rasters = [x for x in glob.iglob(r'X:\temp\**\*.tif', recursive=True)]