Re: Structured programming with optionParser

2010-08-31 Thread NickC 
On Mon, 30 Aug 2010 21:19:08 -0700, Michele Simionato wrote:

 Perhaps, I should give an example of using plac.

 
 For more (including managing options, which I have not shown here) you
 should check the full documentation of plac. I have just uploaded
 release 0.7.2, which is required for this example to work.

Many thanks, very useful.



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Structured programming with optionParser

2010-08-30 Thread NickC 

I'm writing a short (200 lines) script that has half-a-dozen parameter
options, and using optionParser to process the options.

I try to write well-written procedural programmes with functions doing one
thing well, and so on.  The problem I'm getting is that, inevitably, the
function that uses OptionParser ends up doing all the work.

So, I have a brief 6-line main() that calls other functions, a setup(), a
couple of ancillary functions, and a whopping doOptionParsing() that is
over 100 lines long.  doOptionParsing is doing all the work.

I'm struggling to see how you could refactor the option parsing function.
After all, it has to process the options, so it has to do all the setup
for those options, and then process them.

Does anyone have some sort of design pattern or standard template approach
to doing option parsing?  Or perhaps should I make optionParser variables 
global?

Thanks,

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Re: Structured programming with optionParser

2010-08-30 Thread Michele Simionato 
On Aug 31, 3:45 am, NickC reply...@works.fine.invalid wrote:
 I'm struggling to see how you could refactor the option parsing function.
 After all, it has to process the options, so it has to do all the setup
 for those options, and then process them.

Perhaps plac could simplify your life, by removing most of the
boilerplate of
option parsing:  http://pypi.python.org/pypi/plac
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Re: Structured programming with optionParser

2010-08-30 Thread Michele Simionato 
Perhaps, I should give an example of using plac.

For instance, here is how you could implement a SVN-like
tool with two commands ``checkout`` and ``commit``. The trick is to
write a class with two methods ``checkout`` and ``commit`` and an
attribute ``.commands`` listing them, and to call the class with
``plac.Interpreter.call``::

  $ cat vcs.py
  class VCS(object):
  A fictitious version control tool
  commands = ['checkout', 'commit']
  def checkout(self, url):
  return 'ok'
  def commit(self):
  return 'ok'

  if __name__ == '__main__':
  import plac; plac.Interpreter.call(VCS)

The line ``plac.Interpreter.call`` instantiates the ``VCS`` class by
passing
to it the arguments in the command line and then
calls the appropriate method.

You can use the script as follows::

 $ python vcs.py -h
 usage: vcs.py [-h] [args [args ...]]

 positional arguments:
   args

 optional arguments:
   -h, --help  show this help message and exit

 $ python vcs.py checkout url
 ok
 $ python vcs.py commit
 ok

plac_ takes care of parsing the command line, giving the correct error
message if you pass wrong arguments or not enough arguments::

 $ python vcs.py checkout
 usage:  checkout url
  checkout: error: too few arguments

You should realize that there is no real difference between a
command-line argument parser featuring subcommands and an command
interpreter, therefore the previous script also works as an
interactive interpreter::

 $ python vcs.py -i
 i .help

 special commands
 
 .help  .last_tb

 custom commands
 ===
 checkout  commit

 i checkout url
 ok
 i commit
 ok

There is full help support, i.e. you can ask for ``.help command``
for any command, including the special ones such as ``.help`` and
``.last_tb``.
There is full support for autocompletion and command history too,
provided
you have the readline library installed (on Unices) or the pyreadline
library (on Windows).

plac also support a batch mode: you can write a set of commands on
a file and have them executed by the plac runner.

::

 $ echo vcs-commands.plac
 #!vcs.py:VCS
 checkout url
 # nontrivial commands here
 commit

 $ plac_runner.py --batch vcs-commands.plac
 ok
 skip #lines with comments are skipped
 ok

For more (including managing options, which I have not shown here) you
should check the full documentation of plac.
I have just uploaded release 0.7.2, which is required for this example
to work.
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