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I've been trying to teach myself Python scripting for ArcGIS and have gotten frustrated on multiple occasions when I try to debug my script endlessly, only to later find out that it actually works properly when it is loaded into the Python shell in ArcGIS. In the past I have received a variety of errors when running the script in PythonWin, only to have the code work just fine when loaded into ArcGIS.

Why is there a discrepancy between the results of a script run in PythonWin and the Python shell in ArcGIS?

I am using:

  • Windows 8.1
  • Python 2.7.2
  • PythonWin (pywin 32 build 214)
  • ArcGIS 10.1 Advanced

The script is as follows:

#    Import arcpy, env
import arcpy
from arcpy import env

##   Enable file overwrite
env.overwriteOuput = True

#   Set workspace
env.workspace = "c:/documents/arcgis/arcgis tutorials/psu tutorials/lesson3practiceexercisea/washington.gdb"

#   Create new layer feature classes: Cities, ParkAndRide
try:
    arcpy.MakeFeatureLayer_management("CityBoundaries", "CityBoundariesLayer")
    arcpy.MakeFeatureLayer_management("ParkAndRide", "ParkAndRideLayer")
except:
    print "Could not make new layer."

I initially did not post the code because I've had this issue before with code of various types and I was thinking this was not a code error. This code works when loaded the the Python console in ArcGIS, but now when run from PythonWin.

PolyGeo
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Jyler
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    Can you post the script in question? Without that it's going to be hard to see what's wrong. – blah238 Nov 19 '13 at 22:14
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    Do you have the 64-bit Geoprocessing Background Processing option installed? When you install 64-bit Python along with 32-bit, it can do odd things. – MLowry Nov 19 '13 at 22:20
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    You're being too vague in your question. Please edit it with specific examples. – Jason Scheirer Nov 19 '13 at 22:31
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    Much better. Could you also include your error message? And see if changing env.overwriteOuput to env.overwriteOutput (typo) fixes it. – Jason Scheirer Nov 20 '13 at 01:44
  • Remove the try/except so that errors bubble up to the interpreter instead of being concealed. – blah238 Nov 20 '13 at 01:48
  • I fixed the overwrite typo, removed the try-except, and disabled background geoprocessing. The code still runs in ArcGIS, but not from PythonWin. Returns Exit Code 0. I made sure there were file locks before running the updated code, so that's not the issue, either. – Jyler Nov 20 '13 at 02:26
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    Exit code 0 means there was no error. Assuming you get that after removing the try/except, then everything is working fine. The "problem" is that you aren't doing anything that has any visible effect (Make Feature Layer creates a temporary layer that only exists within the current Python session). The comment "Create new layer feature classes" suggests a common misunderstanding of the purpose of feature layers and feature classes. See this question for clarification: What's the difference between feature class and feature layer? – blah238 Nov 20 '13 at 02:36
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    Thanks @blah238. I kept checking for a file in the gdb and wasn't seeing it show up and thought there was an issue. Rookie mistake I suppose, but I can't say I didn't learn something. – Jyler Nov 20 '13 at 03:18

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