topic Re: arcpy.Exists & arcpy.ListFeatureClasses and wildcards in Python Questions

arcpy.Exists & arcpy.ListFeatureClasses and wildcards

BradJones — Sat, 11 Dec 2021 06:10:26 GMT

I have a gdb with around 200 feature classes (waterlines). I working on a tool that will add the featureclass desired base on an ID number. the featureclasses are named "WATERLINE_<ID NUMBER>_<NAME>". Example: WATERLINE_123_SPRINGFIELD. Since the only parameter is entered as a 3 digit ID number (string) I use a wildcard query with arcpy.ListFeatureClasses then use arcpy.Exists to add it to the map. Some systems don't have waterline data. This approach isn't working. If I hardcode the featureclass name into arcpy.Exists it works. Any ideas are appreciated.

# Import modules
import arcpy

# Set overwrite option
from arcpy import env
env.overwriteOutput = True

# Variables
pws = arcpy.GetParameterAsText(0)

waterlines = "WATERLINE_" + pws + "_*"
wl_layer = "Waterlines " + pws
wl_symb = r"G:\Source Water Protection\PWS_ID_Tool\WATERLINES.lyr"


# Add waterlines
env.workspace = r"G:\WATER_FACILITY\WATERLINES.gdb"
wlFclass = arcpy.ListFeatureClasses(waterlines)
arcpy.AddMessage(wlFclass)  # Print/message statement for results dialog box. Confirms wlFclass is there.
if arcpy.Exists(wlFclass):  # This where it fails.
    arcpy.AddMessage("Waterline data exist for this PWS.")
    arcpy.MakeFeatureLayer_management(waterlines, wl_layer)
    arcpy.ApplySymbologyFromLayer_management(wl_layer, wl_symb)
    newLayer = arcpy.mapping.Layer(wl_layer)
    arcpy.mapping.AddLayer(df, newLayer, "TOP")
else:
    arcpy.AddWarning("No waterline data exist for this PWS.")

Tool results dialog box:

Executing: waterlinestest 465

Start Time: Wed Sep 09 10:36:53 2015

Running script waterlinestest...

[u'WATERLINE_123_SPRINGFIELD']

No waterline data exist for this PWS.

Completed script waterlinestest...

Succeeded at Wed Sep 09 10:37:27 2015 (Elapsed Time: 33.95 seconds)

5 (Elapsed Time: 33.95 seconds)

Re: arcpy.Exists & arcpy.ListFeatureClasses and wildcards

WesMiller — Sat, 11 Dec 2021 06:10:28 GMT

You are passing a list where you need a path to "Exists"

import arcpy, os 
workspace =  r"G:\WATER_FACILITY\WATERLINES.gdb"  
wlFclass = arcpy.ListFeatureClasses(waterlines)
if arcpy.Exists(os.path.join(workspace,wlFclass[0])):
  print 'yes'

Re: arcpy.Exists & arcpy.ListFeatureClasses and wildcards

FreddieGibson — Wed, 09 Sep 2015 16:54:05 GMT

If you're getting the names of the feature classes via arcpy.ListFeatureClasses is there a reason why you'd need to check if they exist? The ListFeatureClasses method would only list the feature classes if they existed.

Re: arcpy.Exists & arcpy.ListFeatureClasses and wildcards

BradJones — Wed, 09 Sep 2015 19:09:31 GMT

I need ListFeaturecClasses because i'm working from a wildcard querry. I can't use a wildcard with Exists.

Re: arcpy.Exists & arcpy.ListFeatureClasses and wildcards

BradJones — Sat, 11 Dec 2021 06:10:31 GMT

this is the code block that works. I needed the for loop to convert the unicode list of one featureclass to a 'regular' string. thanks for pointing out my stupid mistake.

# Import modules
import arcpy
import os


# Set overwrite option
from arcpy import env
env.overwriteOutput = True


pws = arcpy.GetParameterAsText(0)


waterlines = "WATERLINE_" + pws + "_*"
wl_layer = "Waterlines " + pws
wl_symb = r"G:\Source Water Protection\PWS_ID_Tool\WATERLINES.lyr"


# Set current mxd and dataframe.
mxd = arcpy.mapping.MapDocument("CURRENT")
df = arcpy.mapping.ListDataFrames(mxd, "")[0]


# Add waterlines
env.workspace = r"G:\WATER_FACILITY\WATERLINES.gdb"
wlFclass = arcpy.ListFeatureClasses(waterlines)
arcpy.AddMessage(wlFclass)
for wl in wlFclass:
  wlPath = os.path.join(env.workspace,wl)
  if arcpy.Exists(wlPath):
    arcpy.AddMessage("Waterline data exist for this PWS.")
    arcpy.MakeFeatureLayer_management(wlPath, wl_layer)
    arcpy.ApplySymbologyFromLayer_management(wl_layer, wl_symb)
    newLayer = arcpy.mapping.Layer(wl_layer)
    arcpy.mapping.AddLayer(df, newLayer, "TOP")
  else:
    arcpy.AddWarning("No waterline data exist for this PWS.")

Re: arcpy.Exists & arcpy.ListFeatureClasses and wildcards

WesMiller — Wed, 09 Sep 2015 19:19:34 GMT

Glad to hear you got it working

Re: arcpy.Exists & arcpy.ListFeatureClasses and wildcards

MichaelSouffront — Wed, 09 Sep 2015 22:28:56 GMT

What about replacing the exists function in line 20 with an "if statement". The listfeatures function returns a list and then you could do something like "if len(list) == 1:" or similar

Re: arcpy.Exists & arcpy.ListFeatureClasses and wildcards

DarrenWiens2 — Wed, 09 Sep 2015 23:02:49 GMT

I agree you don't need Exists. You could check the length of the returned list of feature classes to see if any match.

len(wlFclass)

Re: arcpy.Exists & arcpy.ListFeatureClasses and wildcards

BradJones — Thu, 10 Sep 2015 16:00:36 GMT

Yes, you all are correct. I didn't think about that!