[GIS] Append to text file using ArcGIS and Python

arcgis-9.3arcpypython-script-tool

I have wrote a small routine using Python for ArcGIS (9.3) that will get the count of 2 data layers, calc a percentage, and then write the text back to a text file (CSV) to create a sort of "report" that can be opened in excel and formatted. I want to be able to run this routine on many different dataset pairs and append the data to the end of my CSV report.

The problem is that I am having is that when I attach this Python script to an ArcGIS Script Tool, it automatically erases the file. I am testing that with

if os.path.exists(file):

right off the bat and this response is always "file does not exist". I have tried setting

gp.OverwriteOutput = 0

with no success, and am appending to the file using

fwrite = open(file, 'a')

Does anyone have a workaround that will allow me to choose an output file but NOT overwrite the output?

Best Answer

After some discussion with an Esri rep, I know have a solution and answer to WHY this issue is not really a bug (which I agree with). The reason this isn't really a bug is because Input is meant for files that already exist, Output is meant for new files, and I was trying to use the file selector as both either one. Ultimately this is just semantics but makes sense when you think about it.

Now the solution... In my dialog I created 3 input boxes: 1) A Required string type with Direction = Input and Value List = "New", "Append", 2) an Optional file type with Display name = "New", Direction = Output, and 3) an Optional file type with Display Name = "Existing", Direction = Input.

enter image description here

Now, in order to control which input box opens, thereby allowing my to choose either an output (new) or input (existing) file, I needed to put some code into the ToolValidator (Properties->Validation tab). Under the def initializeParameters(self) category I added the following code to disable the New & Existing file input boxes at startup:

self.params[1].Enabled = 0 # 0 = Disabled, 1 = Enabled on load
self.params[2].Enabled = 0 #Disable on load

and under the def updateParameters(self) category I added the following code to enable the correct file box based upon if I wanted to create a New or Append to existing file:

import sys, string, os
ftype = str(self.params[0].value)
if ftype == "New":
  self.params[1].Enabled = 1 #
elif ftype == "Append":
  self.params[2].Enabled = 1

Then from within my scripting code, I can just identify which option was selected for the 1st parameter (New or Append), and grab the text string from the appropriate optional file string from parameter 2 or 3 with a simple If/Then statement.

More details on programming the ToolValidator here: http://webhelp.esri.com/arcgiSDEsktop/9.3/index.cfm?TopicName=Programming_a_ToolValidator_class

Related Solutions

[GIS] Building Python script that exports to several output files using ArcGIS Desktop

I guess this depends on how often you want to run the script, whether or not you want to hard code in the clip grids and the output shapefiles.

Very simply, I'd have a dictionary, of clip_grid : output_shapefile, loop through that and spit out the output.

import arcgisscripting
#Create the geoprocessor
gp = arcgisscripting.create(9.3)

input_shape = "yourshapefile.shp" #<-- this single file will be clipped repeatedly

#grids and corresponding outputs go here
clip_dictionary = {"clipgrid1.shp":"output1.shp", "clipgrid2.shp":"output2.shp"}

for iter in clip_dictionary:
    #Clip_analysis (in_features, clip_features, out_feature_class, cluster_tolerance)
    gp.Clip_analysis(input_shape, iter, clip_dictionary[iter])

Hope that helps!

sys.argv is a possiblity if you wish to read in the arguments from the command line (or if you wish to add the script to the toolbox). You could also use getopt or optparse as well.

Assume that we have a script called clip_export.py, which we wish to pass a list of inputs. We could run the script like:

clip_export.py input_shape clipshape_1;clipshape_2;clipshape_3 output_folder

Note that this is similar to the input that is sent to a python script by Toolbox.

At any rate, you can read this in your script like so:

import sys

input_shape = sys.argv[1] #<-- Note that the 0th argument in sys.argv is the script name

clip_shape_list = sys.argv[2].split(';') #<-- splits the second argument on the semicolon into a python list

output_folder = sys.argv[3]

The from here run the rest of your script. As @Simon Norris shows below.

Again, hope this helps!

[GIS] Controlling Overwrite Behavior in ArcGIS Python Script Tool Validation

What direction is your "Output File" parameter set to? Because if the output file already exists, and the parameter direction is output, the geoprocessing framework will automatically overwrite the output if the option to overwrite is set in the user's geoprocessing options, or error out otherwise, and I'm not sure you can override this in the ToolValidator.

It might be easier to use two input parameters instead; a folder (directory) and a filename (string), and then handle your overwrite logic in your script, not your validation routine. Often times this is better practice anyways since you may want to be able to run your script standalone.

Best Answer

Related Solutions

[GIS] Building Python script that exports to several output files using ArcGIS Desktop

[GIS] Controlling Overwrite Behavior in ArcGIS Python Script Tool Validation

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