使用argparse或docopt来替换pdftk

Question

我正在编写一个接受如下形式参数的程序。

SYNOPSIS
pdf_form.py <input PDF file | - | PROMPT> [ <operation> <operation arguments> ]
    [ output <output filename | - | PROMPT> ] [ flatten ]
Where:
    <operation> may be empty, or: [generate_fdf | fill_form |dump_data | dump_data_fields ]
OPTIONS
--help, -h
    show summary of options.
<input PDF files | - | PROMPT>
    An input PDF file. Use - to pass a single PDF into pdftk via stdin.
[<operation> <operation arguments>]
    Available operations are:
    generate_fdf,fill_form, dump_data,dump_data_fields
    Some operations takes additional arguments, described below.
    generate_fdf
        Reads a single, input PDF file and generates an FDF file suitable for fill_form out of it
        to the given output filename or (if no output is given) to stdout. Does not create a new PDF.
    fill_form <FDF data filename | - | PROMPT>
        Fills the input PDF's form fields with the data from an FDF file, or stdin.
        Enter the data filename after fill_form, or use - to pass the data via stdin, like so:
        ./pdf_form.py form.pdf fill_form data.fdf output form.filled.pdf
        After filling a form, the form fields remain interactive unless flatten is used.
        flatten merges the form fields with the PDF pages. You can also use flatten alone, as shown:
        ./pdf_form.py form.pdf fill_form data.fdf output out.pdf flatten
        or:
        ./pdf_form.py form.filled.pdf output out.pdf flatten
    dump_data
        Reads a single, input PDF file and reports various statistics,  to the given output filename or (if no output is given).
    dump_data_fields
         Reads a single, input PDF file and reports form field statistics to the given output filename
[flatten]
    Use this option to merge an input PDF's interactive form fields and their data with the PDF's pages.

我目前正在使用以下(混乱)代码解析这些选项

def parse(arg):
    """ Parses commandline arguments. """
    #checking that request is valid
    if len(arg) == 1:
        raise ValueError(info())
    if arg[1] in ('-h', '--help'):
        print(info(verbose=True))
        return
    if len(arg) == 2:
        raise ValueError(info())
    path = arg[1]
    if path == 'PROMPT':
        path = input('Please enter a filename for an input document:')
    func = arg[2]
    if func == 'fill_form':
        fdf = arg[3]
        if len(arg) > 5 and arg[4] == 'output':
            out = arg[5]
        else:
            out = '-'
    else:
        fdf = None
        if len(arg) > 4 and arg[3] == 'output':
            out = arg[4]
        else:
            out = '-'
    if out == 'PROMPT':
        out = input('Output file: ')
    flatten = 'flatten' in arg
    return path, func, fdf, out, flatten

是否有更好的方法使用argparse或docopt来做到这一点?

Answer 1

一个参数可以是

parser.add_argument('-o','--output', default='-')

和

if args.output in ['PROMPT']:
    ... input...

:

parser.add_argument('--flatten', action='store_true')
parser.add_argument('--fill_form', dest='ftd')
parser.add_argument('--path')
if args.path in ['PROMPT']:
     args.path = input...