PythonTemplate

I write a lot of Python code, both for stand-alone scripts and script tools. Over the years, I’ve developed a template that I use for all my Python code. It keeps my code organized and consistent — the first step towards making reusable code.

My template is shown below. Some of the features of this template are:

• Most-used modules (os, sys, arcpy) are imported
• Both system and arcpy exceptions are handled
• Any number of input parameters (arguments) are allowed
• The statement if __name__ == ‘__main__’:
  evaluates to true whenever the file is run as a stand-alone script or as a geoprocessing script tool. The statement evaluates to false if the file is imported as a module in another Python script — this allows you to use all the functions you defined in the file as a Python module. Essentially, the if __name__ block short circuits the execution of the code in that block unless the Python script it lives in is the one being run.

Here’s my template:

# Copyright:   (c) company name
# ArcGIS Version:   10
# Python Version:   2.6
#--------------------------------
import os
import sys
import arcpy
def do_analysis(*argv):
    """TODO: Add documentation about this function here"""
    try:
        #TODO: Add analysis here
        pass
    except arcpy.ExecuteError:
        print arcpy.GetMessages(2)
    except Exception as e:
        print e.args[0]
# End do_analysis function

# This test allows the script to be used from the operating
# system command prompt (stand-alone), in a Python IDE, 
# as a geoprocessing script tool, or as a module imported in
# another script
if __name__ == '__main__':
    # Arguments are optional
    argv = tuple(arcpy.GetParameterAsText(i)
        for i in range(arcpy.GetArgumentCount()))
    do_analysis(*argv)

Starting from the sample template above, here is a script that merges multiple feature classes from an input workspace using geoprocessing tools.  The “do_analysis” routine is renamed to “merge”:

#-------------------------------------------------------------
# Name:       merge.py
# Purpose:    Merge multiple feature classes from a workspace.
# Author:     esri
# Created:    23/06/2011
# Copyright:   (c) esri
# ArcGIS Version:   10
# Python Version:   2.6
#-------------------------------------------------------------
import os
import sys
import arcpy

def merge(input_workspace, output_feature_class):
    """Merge multiple feature classes from a workspace into a
       new output feature class."""
    try:
        arcpy.env.overwriteOutput = True
        arcpy.env.workspace = input_workspace
        fcs = arcpy.ListFeatureClasses('*')

        # Run merge with the list of feature classes as input
        arcpy.Merge_management(fcs, output_feature_class)

    except arcpy.ExecuteError:
        print arcpy.GetMessages(2)
        arcpy.AddError(arcpy.GetMessages(2))
    except Exception as e:
        print e.args[0]
        arcpy.AddError(e.args[0])

# End main function

if __name__ == '__main__':
    argv = tuple(arcpy.GetParameterAsText(i)
                 for i in range(arcpy.GetArgumentCount())
    merge(*argv)

Several Python IDEs give you an option to specify a template to use anytime you create a new .py file. Here is two examples of Python IDE’s that make creating and using templates easy:

PyScripter

1. Go to Tools > Options > File templates…
2. Enter a name
3. Provide a default extension (i.e. .py)
4. Enter “Python” for the Category
5. Enter your Python code in the Template box
6. Click the Add button

Wingware’s Python IDE

1. Go to Tools > Templates — a new Template window opens.
2. In the Template window, right-click and Add new template…
3. Add the template code in the editor and save.

For a complete list of Python Integrated Development Environments, visit http://wiki.python.org/moin/IntegratedDevelopmentEnvironments

It’s understood no single template can be used to start every project. You may require a library of templates. A template library becomes a go to place for you and your colleagues.

Additional Resources

• PEP 8 – Style Guide for Python Code – A recommended resource to use when writing Python scripts is the PEP 8 – Style Guide for Python Code. This style guide gives you standard coding conventions to use when writing Python code.
• PYCH – Online Python Code Checker – This online Python code checker, checks your Python code for errors and pep8 deviations.

This post contributed by Jason Pardy, a product engineer on the Analysis and Geoprocessing team