Loop with arcpy.ListFiles

Question

I'm super new on here and have also not much experience with Python but I really like to learn to work with this language. I'm tying to write a script for this:

enter image description here

I think I need a for loop instead the 'Iterate Datasets' from the ModelBuilder but how can I program it with using arcpy.ASCIIToRaster_conversion, arcpy.DefineProjection_management, arcpy.AddField_management, arcpy.CalculateField_management. This is what I could export from the ModelBulider to a Python script:

# Import arcpy module
import arcpy
# Load required toolboxes
arcpy.ImportToolbox("Modellfunktionen")
arcpy.ImportToolbox("D:/Julia_T/projekt/erste_schritte/zweiter_tag_a1/a1_prozent.tbx")
# Local variables:
testdatenB = "D:\\Julia_T\\projekt\\MODIS\\karadarya\2000円_neu\\testdatenB"
File_asc = "D:\\Julia_T\\projekt\\MODIS\\karadarya\2000円_neu\\testdatenB\2000112円_cloud_fr=e.asc"
v_Name__output_img = "D:\\Julia_T\\projekt\\erste_schritte\\zweiter_tag_a1\\ergebnisse\\test_c\\ergebnisse\\%Name%_output.img"
v_Name__output_img__2_ = "D:\\Julia_T\\projekt\\erste_schritte\\zweiter_tag_a1\\ergebnisse\\test_c\\ergebnisse\\%Name%_output.img"
v_Name__output_img__3_ = "D:\\Julia_T\\projekt\\erste_schritte\\zweiter_tag_a1\\ergebnisse\\test_c\\ergebnisse\\%Name%_output.img"
# Process: Dateien iterieren
arcpy.IterateFiles_mb(testdatenB, "*", "asc", "NOT_RECURSIVE")
# Process: ASCII in Raster
arcpy.gp.toolbox = "D:/Julia_T/projekt/erste_schritte/zweiter_tag_a1/a1_prozent.tbx";
# Warning: the toolbox D:/Julia_T/projekt/erste_schritte/zweiter_tag_a1/a1_prozent.tbx DOES NOT have an alias. 
# Please assign this toolbox an alias to avoid tool name collisions
# And replace arcpy.gp.ASCIIToRaster(...) with arcpy.ASCIIToRaster_ALIAS(...)
arcpy.gp.ASCIIToRaster(File_asc, v_Name__output_img, "INTEGER")
# Process: Projektion definieren
arcpy.gp.toolbox = "D:/Julia_T/projekt/erste_schritte/zweiter_tag_a1/a1_prozent.tbx";
# Warning: the toolbox D:/Julia_T/projekt/erste_schritte/zweiter_tag_a1/a1_prozent.tbx DOES NOT have an alias. 
# Please assign this toolbox an alias to avoid tool name collisions
# And replace arcpy.gp.DefineProjection(...) with arcpy.DefineProjection_ALIAS(...)
arcpy.gp.DefineProjection(v_Name__output_img, "GEOGCS['GCS_WGS_1984',DATUM['D_WGS_1984',SPHEROID['WGS_1984',6378137.0,298.257223563]],PRI MEM['Greenwich',0.0],UNIT['Degree',0.0174532925199433]]")
# Process: Feld hinzufügen
arcpy.gp.toolbox = "D:/Julia_T/projekt/erste_schritte/zweiter_tag_a1/a1_prozent.tbx";
# Warning: the toolbox D:/Julia_T/projekt/erste_schritte/zweiter_tag_a1/a1_prozent.tbx DOES NOT have an alias. 
# Please assign this toolbox an alias to avoid tool name collisions
# And replace arcpy.gp.AddField(...) with arcpy.AddField_ALIAS(...)
arcpy.gp.AddField(v_Name__output_img__2_, "Prozent", "DOUBLE", "", "", "", "", "NULLABLE", "NON_REQUIRED", "")
# Process: Feld berechnen
arcpy.gp.toolbox = "D:/Julia_T/projekt/erste_schritte/zweiter_tag_a1/a1_prozent.tbx";
# Warning: the toolbox D:/Julia_T/projekt/erste_schritte/zweiter_tag_a1/a1_prozent.tbx DOES NOT have an alias. 
# Please assign this toolbox an alias to avoid tool name collisions
# And replace arcpy.gp.CalculateField(...) with arcpy.CalculateField_ALIAS(...)
arcpy.gp.CalculateField(v_Name__output_img__3_, "Prozent", "([Count]/53959)*100", "VB", "")

I thing my main problem is how to program the loop by using the last created raster in the next tool. I have folders (15) with around 350 asc files which should turn through this loop. The result should be written in a new folder with the same name plus the new type (img). Is there something I need to do with the workspace or is it like this?

import arcpy
from arcpy import env
env.workspace = r"D:\Julia_T\projekt\MODIS\karadarya2000円_neu\testdatenB"

• PolyGeo: Welcome to GIS SE! Would you be able to edit your question to include the version of ArcGIS for Desktop that you are using, please? My quick advice on this one is NOT to try and debug your script from ModelBuilder but instead to step through one iteration by manually running each tool in sequence and then using Copy As Python Snippet in the Geoprocessing | Results window to write a Python script to repeat what you just did. Once that works showing you how to include iteration in the Python script becomes trivial.
• Nora: I'm working with ArcMap 10.2.1, thanks for asking. You mean I should first write a skript with the geoprocessingtools for just one asc file and add the loop afterwards?
• PolyGeo: Yes - I think writing the script using the Geoprocessing tools (and Copy As Python Snippet to get the syntax) for just one *.asc file , and then adding the loop afterwards is a much easier way to do it.
• Nora: Thanks a lot, I'm sill trying. (Perhaps it will take some time, but I like to find my way. For sure I will pose my result.)

Answer 1

The ModelBuilder functions (like arcpy.IterateFiles_mb) only work within ModelBuilder, and don't do as desired within a Python script. But, for loops do just as well (if not better).

In this case, you want to loop through all the .asc files in a workspace.

Define the workspace (you got that far):

import arcpy
from arcpy import env
env.workspace = r"D:\Julia_T\projekt\MODIS\karadarya2000円_neu\testdatenB"

Use the List Files function to create a list of all the .asc files in the workspace

ascFileList = arcpy.ListFiles("*.asc")
for ascFile in ascFileList:
 # geoprocessing steps

Or, a simpler version that does the same thing:

for ascFile in arcpy.ListFiles("*.asc"):
 # geoprocessing steps

Run arcpy tools on each file by putting them under the for loop. (Note: pay attention to indentation. It is one of the few things Python is picky about.)

for ascFile in arcpy.ListFiles("*.asc"):
 # get the file name without extension (replaces the %Name% variable from ModelBuidler)
 ascFileName = os.path.splitext(ascFile)[0]
 # define the output file
 rastFile = ascFileName + "_output.img"
 # run the tool
 arcpy.ASCIIToRaster_conversion(ascFile, rastFile, "INTEGER")

A couple of notes about exported python scripts -- not only do iterators not work, but the tool syntax is old (for example, arcpy.gp.ASCIIToRaster should now be arcpy.ASCIIToRaster_conversion. I always recommend quickly looking up the ArcGIS Help pages for any given geoprocessing function to see what the current syntax and input variables should be. It is often faster to make the script from scratch instead of exporting a ModelBuilder tool and cleaning up the code.

• Nora: Thanks so much for you answer, you saved my day. I'm excited to try it. But first I should do a research about the part with the name because I tried it before without and for sure it hadn't worked.
• Erica: I like to use a lot of print statements to check the value of variables before I add in the actual geoprocessing steps. Or, if you're running this as an ArcMap tool instead of in IDLE, using arcpy.AddMessage(variable)
• Nora: Sorry for asking again, but I don't know what I'm doing wrong. I always get the errow 000865 0. Do I have to use the CatalogPath?
• Erica: It's not a problem to keep asking, but you should to ask a new Question specific to that error (and show what updated code you're using) -- it's easier to work with than in Comments :)
• Nora: the error 000865 is fixed, see (gis.stackexchange.com/questions/108131/…). Thanks so much

Answer 2

Another non-proprietary python option to list files is os.walk:

import os
for root, dirs, files in os.walk('C:/Temp'):
 for f in files:
 if f.endswith('.asc'):
 print os.path.join(root, f)

The benefit of this method opposed to

arcpy.ListFiles

is that it can recursively search through sub-directories.

• Paul: I wonder speed wise how this matches up against the various arcpy.List*() functions. I usually use a mixture of both, sometimes together.

Answer 3

Ok, it is done know – my first script. Thanks for your support!

import arcpy
import os
from arcpy import env
env.overwriteOutput = True
env.workspace = r"D:\Julia_T\projekt\erste_schritte\test_projection"
#folder to list
ascFileList = arcpy.ListFiles("*.asc")
print ascFileList
#works
for ascFile in ascFileList:
 # geoprocessing steps
 ascFileName = os.path.splitext (ascFile)[0]
 print ascFileName
 #works
 rastFile = ascFileName + "_output.img"
 print rastFile
#works
#run the tool
arcpy.ASCIIToRaster_conversion (env.workspace + "\\" + ascFile, env.workspace + "\\" + rastFile, "INTEGER")
# Process: Projektion definieren
arcpy.DefineProjection_management (env.workspace + "\\" + rastFile, "GEOGCS['GCS_WGS_1984',DATUM['D_WGS_1984',SPHEROID['WGS_1984',6378137.0,298.257223563]],PRIMEM['Greenwich',0.0],UNIT['Degree',0.0174532925199433]]")
# Process: Feld hinzufügen
arcpy.AddField_management (env.workspace + "\\" + rastFile,"Prozent","DOUBLE")
# Process: Feld berechnen
arcpy.CalculateField_management(env.workspace + "\\" + rastFile,"Prozent","( [Count] /53959) *100", "VB")