Package: sh2py
# sh2pysh2py is a shell to Python command line mapper. In other words, it is theeasiest way to expose Python functions to the shell. Main features:* Very small code size. A single Python module. About a hundred lines of code.* The public API consists of a Python class, `CommandLineMapper`; plus twomethods: `add` and `run`.* No external dependencies.* Support for Python 2 and 3.## Installationpip install sh2py## Basic UseExpose a single Python function. Consider the snippet below.```pythonfrom sh2py import CommandLineMapperdef myfunc(arg1, arg2, arg3='val'):print(arg1)print(arg2)print(arg3)if __name__ == '__main__':cli = CommandLineMapper()cli.add(myfunc)cli.run()```The last three instructions demonstrate the basic operation of the API.1. Instantiate the `CommandLineMapper`.2. Register the function you want to expose, using the `CommandLineMapper.add`method.3. Call `CommandLineMapper.run`. It will process the command line,``sys.argv``, and invoke the matching function.Suppose the snippet above is saved as `myscript.py`.$ python myscript.py val1 val2 arg3=val3val1val2val3The output reveals that the shell command above actually called`myfunc('val1', 'val2', arg3='val3')`. A couple of notes.1. Only one function was exposed via `CommandLineMapper.add`, so its name couldbe omitted from the command line. If exposing more than one function, it isrecommended to pass its name as the first program argument, otherwise the firstexposed function will be called. See next section.2. There is no type validation/coercion. The **run** method will only passstrings on actual function calls.## Multiple CommandsIf your script is large, you can organize it as a suite of sub-commands. Createone function for each command you expect to handle and register all of themwith `CommandLineMapper.add`. Consider the code below.```pythonfrom sh2py import CommandLineMapperdef subcommand1(*args1, **kwargs1):passdef subcommand2(*args2, **kwargs2):passif __name__ == '__main__':cli = CommandLineMapper()cli.add(subcommand1)cli.add(subcommand2)cli.run()```You can then specify which function to run via command line. For example, toinvoke `subcommand2` with arguments `val1` and `val2`, type the following.python mysuite.py subcommand2 val1 val2Notice that the `subcommand2` entry itself is extracted from the argumentline. The remainder of the line is processed as usual. In this case, `args2`is `['val1', 'val2']`.## Complete exampleHere is a complete example.```pythonfrom sys import exit, stderrfrom time import sleepfrom random import samplefrom sh2py import HALT, CommandLineMapperdef hello(case='', shuffle='no', pace='0'):'''Emits a "Hello, world!" greeting message on standard error.Usage:python hello.py helppython hello.py [case=upper/lower] [shuffle=yes/no] [pace=0]Arguments:help,              print this usage help and exit;case=upper/lower,  convert the message to uppercase, or lowercase;shuffle=yes/no,    shuffle the letters of the message;pace=0,            pace at which the letters are shown, in miliseconds.By default, there is no case conversion and no shuffling. Also, the pace iszero, so the entire message is shown immediately on standard error.'''if case in ['', 'upper', 'lower'] and shuffle in ['yes', 'no']:if pace.isdigit():greet = ['Hello', 'world']delay = int(pace)if shuffle == 'yes':greet[0] = ''.join(sample(greet[0], len(greet[0])))greet[1] = ''.join(sample(greet[1], len(greet[1])))greet = '{}, {}!'.format(*greet)if case == 'upper':greet = greet.upper()elif case == 'lower':greet = greet.lower()if delay == 0:print(greet, file=stderr)else:for x in greet:stderr.write(x)stderr.flush()sleep(delay / 1000.0)print(file=stderr)else:return HALTelse:return HALTif __name__ == '__main__':cli = CommandLineMapper()cli.add(hello)if cli.run() is HALT:print(hello.__doc__, file=stderr)exit(1)```Observe that the `hello` function does not have a `help` argument, but the**docstring** says different. The `help` argument is automatically recognizedand, when used, will print the **docstring** of the default, `hello`, function.A default help text will be printed if a function does not supply a**docstring**.The call to `CommandLineMapper.run` will return `HALT` if a command isinvoked with an invalid syntax. Your functions can also use it to signal errorconditions. This allows the program to exit with a non-zero status, or triggersome error handling function.## Q&AQ. I want POSIX arguments.A. Wrong tool. There are plenty of Python command line parsing utilitiessupporting POSIX. Try one of them.* Argparse/Optparse/Getopt. Built into Python. Complex.* [Compago](https://github.com/jmohr/compago). Very nice, butunmaintained. Also, does not run on Python 3.* [Docopt](http://docopt.org/).* [Clint](https://github.com/kennethreitz/clint).* [Click](http://click.pocoo.org/3/).Q. I need type coercion.A. Implement it yourself, or use some third party library.Q. I can use Python itself as a command line interpreter. Why all of this?A. Yes you can. In this case all of this becomes irrelevant. I prefer not to,that is one of the reasons I wrote this tool. Another is that everything elseis too complex. YMMV.Q. Why not use `sys.argv` directly.A. Good question. I do this a lot of times. Actually, if your script is smallenough and requires zero, one, or maybe two positional parameters, there is noneed for command line processing tools. Write a couple of conditionals andprint a simple help message in case of errors.