LegacyPythonTutorial

Creating a Python script

This tutorial will demonstrate how to use the The program interface definition framework to write a Python script where usage and command line option parsing is automatically generated.

• [Creating a Python script](#Creating a Python script)
  • [Step 1. Defining the options](#Step 1. Defining the options)
  • [Step 2. Write your code](#Step 2. Write your code)
  • [Step 3. Build](#Step 3. Build)
  • [Step 4. Run!](#Step 4. Run!)
  • [Step 5. Beyond the Python script](#Step 5. Beyond the Python script)
    • [Auto complete](#Auto complete)

Step 1. Defining the options

The first step is to describe the program options in a XML file. The XML elements have to follow the program interface XML Schema. samples/miniapp/miniapp.xml

#!xml
<?xml version="1.0" encoding="utf-8"?>
<prg:program version="2.0" xmlns:prg="http://xsd.nore.fr/program">
	<prg:name>miniapp</prg:name>
	<prg:version>1.0</prg:version>
	<prg:options>
		<prg:switch>
			<prg:databinding>
				<prg:variable>displayHelp</prg:variable>
			</prg:databinding>
			<prg:names>
				<prg:long>help</prg:long>
				<prg:short>h</prg:short>
			</prg:names>
		</prg:switch>
		<prg:argument>
			<prg:databinding>
				<prg:variable>arg</prg:variable>
			</prg:databinding>
			<prg:names>
				<prg:long>some-arg</prg:long>
				<prg:short>a</prg:short>
			</prg:names>
		</prg:argument>
	</prg:options>
</prg:program>

You can use any editor to write this file but an XML editor with auto-completion and XML Schema support will greatly increase the writing speed.

Step 2. Write your code

Let's write a little and useless Python script

#!Python
#!/usr/bin/env python
import Program
import sys

p = Program.Program()
"""Create an instance of your program description""" 

result = p.parse(sys.argv[1:len(sys.argv)])
"""Call the command line parser"""

if result.options.displayHelp:
    print p.usage(result, Program.Usage.Abstract)
    """Print the help message"""
    exit(0)

if not result.is_valid:
    for e in result.issues["errors"]:
        print e
    exit(1)
    
print "--some-arg: " + str(result.options.arg)

Step 3. Build

#!bash
${NS_XML_PATH}/ns/sh/build-python.sh -x miniapp.xml -p miniapp.py

This command line tool will generate a Python module folder where the miniapp.py resides. This module contains a copy of the ${NS_XML_PATH}/ns/python/program/${SCHEMA_VERSION} folder and an additional auto-generated Program.py

Step 4. Run!

#!bash
./miniapp.py --help --some-arg "Bleeeh Blaaah"

You should try to type invalid options or forget the --some-arg argument to see what's happen.

Step 5. Beyond the Python script

Auto complete

To get a bash auto-completion command file, use the bashcompletion.xsl style sheet to transform the option specification file

#!bash
xsltproc -o miniapp-autocomplete.inc.sh --stringparam prg.bash.completion.programFileExtension ".py" ${NS_XML_PATH}/ns/xsl/program/${SCHEMA_VERSION}/bashcompletion.xsl miniapp.xml

Then, include the generated file in your current environment

#!bash
. miniapp-autocomplete.inc.sh

And try typing

#!bash
./miniapp.py -<TAB>

The shell will propose...

#!bash
$ ./miniapp.py -
-a		   -h		   --help	   --some-arg   

See the Bash auto-complete file generation for more details.

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The program interface definition framework