Python clg (command line generator) shelll extensions

clgshell.py

# clgshell
#
# clgshell is an extension to python-clg (command line generator) for writing shell commands
#
# Usage:
#
# 1. create a commands.py file
# 2. import clgshell from there
# 3. use @cmd decorator for defining shell commands
# 4. reference those commands from YAML python-clg spec:
#       execute:
#          file: commands.py
#          function: <name of the defined command>
#
# Syntax:
# 
# Use @cmd decorator wrapping a command function. The command function should return a string to be executed in a shell (via os.system function). Normal console arguments are replaced via python's format function. That means, arguments appear between braces like: {argname}. Also, conditional arguments syntax is supported. Conditional arguments have the following form: ?arg[str]. That means, if arg is passed and not false, then str appears in the shell command.
#
# Example:
#
# @clgshell.cmd
# def docker_run (args):
#    return 'docker run --name simplecal -p {port}:9090 -p ?detached[-d] simplecal'
#
# In the above example, `port` is extracted from command line arguments. Also, if `detached` argument is present and True, then `-d` is added to the command.
#
# from the YAML file:
# run:
#    help: Run an instance of Docker image
#    options:
#      detached:
#        short: d
#        help: Run Docker image detached
#        action: store_true
#      port:
#        short: p
#        default: 9090
#      swank-port:
#        default: 4050
#    execute:
#      file: commands.py
#      function: docker_run

import re
import os

def format_cond(str, **args):
    "Format a string conditionally. Conditions syntax is ?condition[output]"

    regex = r'\?(\w+)\[(.*)\]'

    def replacer(match):
        cond = match.group(1)
        rep = match.group(2)
        if args[cond]:
            # The condition holds. Replace condition body formatting args
            return match.group(2).format(**args)
        else:
            '' # The condition doesn't hold. Replace with empty string
    
    return re.sub(regex, replacer, str)

def cmd (func):
    def cmd_func(args):
        vargs = vars(args)
        cmdstr = func(vargs)
        cmdstr = format_cond(cmdstr, **vargs)
        cmdstr = cmdstr.format(**vargs)
        print cmdstr
        os.system(cmdstr)

    return cmd_func