The argparse module offers a way to do this without implementing your own requiredness checks. The example below uses “subparsers” or “sub commands”. I’ve implemented a subparser for “dump” and one for “format”. import argparse parser = argparse.ArgumentParser() parser.add_argument(‘file’, help=’The file you want to act on.’) subparsers = parser.add_subparsers(dest=”subcommand”) subparsers.required = True # required since … Read more
I do not think it is possible to pass a dictionary as an argument in the command line because there doesn’t exist a conversion function from string to dict (EDIT: A hack is possible which gives similar behaviour, see below). What you are essentially telling python to do is: dict(“{‘key1’: ‘value1’}”) Which if you try … Read more
You can set the default= of the argument to a .get() of os.environ with the environment variable you want to grab. You can also pass a 2nd argument in the .get() call, which is the default value if .get() doesn’t find an environment variable by that name (by default .get() returns None in that case). … Read more
There is a bug report on this: http://bugs.python.org/issue9338 argparse optionals with nargs=”?”, ‘*’ or ‘+’ can’t be followed by positionals A simple (user) fix is to use — to separate postionals from optionals: ./test.py -o 0.21 0.11 0.33 0.13 — 100 I wrote a patch that reserves some of the arguments for use by the … Read more
As of python 2.7, optparse is deprecated, and will hopefully go away in the future. argparse is better for all the reasons listed on its original page (https://code.google.com/archive/p/argparse/): handling positional arguments supporting sub-commands allowing alternative option prefixes like + and / handling zero-or-more and one-or-more style arguments producing more informative usage messages providing a much … Read more
Per the documentation: The type keyword argument of add_argument() allows any necessary type-checking and type conversions to be performed … The argument to type can be any callable that accepts a single string. You could do something like: def valid_date(s): try: return datetime.strptime(s, “%Y-%m-%d”) except ValueError: msg = “not a valid date: {0!r}”.format(s) raise argparse.ArgumentTypeError(msg) … Read more
Take a look at the documentation: https://docs.python.org/3/library/argparse.html#type import argparse parser = argparse.ArgumentParser() parser.add_argument(‘file’, type=argparse.FileType(‘r’)) args = parser.parse_args() print(args.file.readlines())
This answer comes from Steven Bethard on Google groups. I’m reposting it here to make it easier for people without a Google account to access. You can override the default behavior of the error method: import argparse import sys class MyParser(argparse.ArgumentParser): def error(self, message): sys.stderr.write(‘error: %s\n’ % message) self.print_help() sys.exit(2) parser = MyParser() parser.add_argument(‘foo’, nargs=”+”) … Read more
This is a bit tricky, as argparse does not expose a list of defined sub-parsers directly. But it can be done: import argparse # create the top-level parser parser = argparse.ArgumentParser(prog=’PROG’) parser.add_argument(‘–foo’, action=’store_true’, help=’foo help’) subparsers = parser.add_subparsers(help=’sub-command help’) # create the parser for the “a” command parser_a = subparsers.add_parser(‘a’, help=’a help’) parser_a.add_argument(‘bar’, type=int, help=’bar … Read more
I came up with the same qustion, and it seems i have got a better answer. The solution is we shall not simply nest subparser with another subparser, but we can add subparser following with a parser following another subparser. Code tell you how: parent_parser = argparse.ArgumentParser(add_help=False) parent_parser.add_argument(‘–user’, ‘-u’, default=getpass.getuser(), help=’username’) parent_parser.add_argument(‘–debug’, default=False, required=False, action=’store_true’, … Read more