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    <p>The relevant Python bug is <a href="http://bugs.python.org/issue15112" rel="noreferrer">Issue 15112</a>.</p> <blockquote> <p><code>argparse: nargs='*'</code> positional argument doesn't accept any items if preceded by an option and another positional</p> </blockquote> <p>When argparse parses <code>['1', '2', '--spam', '8', '8', '9']</code> it first tries to match <code>['1','2']</code> with as many of the positional arguments as possible. With your arguments the pattern matching string is <code>AAA*</code>: 1 argument each for <code>pos</code> and <code>foo</code>, and zero arguments for <code>vars</code> (remember <code>*</code> means ZERO_OR_MORE). </p> <p><code>['--spam','8']</code> are handled by your <code>--spam</code> argument. Since <code>vars</code> has already been set to <code>[]</code>, there is nothing left to handle <code>['8','9']</code>.</p> <p>The programming change to <code>argparse</code> checks for the case where <code>0</code> argument strings is satisfying the pattern, but there are still <code>optionals</code> to be parsed. It then defers the handling of that <code>*</code> argument.</p> <p>You might be able to get around this by first parsing the input with <a href="https://docs.python.org/3.6/library/argparse.html#argparse.ArgumentParser.parse_known_args" rel="noreferrer"><code>parse_known_args</code></a>, and then handling the <code>remainder</code> with another call to <a href="https://docs.python.org/3.6/library/argparse.html#argparse.ArgumentParser.parse_args" rel="noreferrer"><code>parse_args</code></a>.</p> <p>To have complete freedom in interspersing optionals among positionals, in <a href="http://bugs.python.org/issue14191" rel="noreferrer">issue 14191</a>, I propose using <code>parse_known_args</code> with just the <code>optionals</code>, followed by a <code>parse_args</code> that only knows about the positionals. The <code>parse_intermixed_args</code> function that I posted there could be implemented in an <code>ArgumentParser</code> subclass, without modifying the <code>argparse.py</code> code itself.</p> <hr> <p>Here's a way of handling subparsers. I've taken the <a href="http://bugs.python.org/file30422/intermixed.patch" rel="noreferrer"><code>parse_known_intermixed_args</code></a> function, simplified it for presentation sake, and then made it the <code>parse_known_args</code> function of a Parser subclass. I had to take an extra step to avoid recursion. </p> <p>Finally I changed the <code>_parser_class</code> of the subparsers Action, so each subparser uses this alternative <code>parse_known_args</code>. An alternative would be to subclass <code>_SubParsersAction</code>, possibly modifying its <code>__call__</code>.</p> <pre><code>from argparse import ArgumentParser def parse_known_intermixed_args(self, args=None, namespace=None): # self - argparse parser # simplified from http://bugs.python.org/file30204/test_intermixed.py parsefn = super(SubParser, self).parse_known_args # avoid recursion positionals = self._get_positional_actions() for action in positionals: # deactivate positionals action.save_nargs = action.nargs action.nargs = 0 namespace, remaining_args = parsefn(args, namespace) for action in positionals: # remove the empty positional values from namespace if hasattr(namespace, action.dest): delattr(namespace, action.dest) for action in positionals: action.nargs = action.save_nargs # parse positionals namespace, extras = parsefn(remaining_args, namespace) return namespace, extras class SubParser(ArgumentParser): parse_known_args = parse_known_intermixed_args parser = ArgumentParser() parser.add_argument('foo') sp = parser.add_subparsers(dest='cmd') sp._parser_class = SubParser # use different parser class for subparsers spp1 = sp.add_parser('cmd1') spp1.add_argument('-x') spp1.add_argument('bar') spp1.add_argument('vars',nargs='*') print parser.parse_args('foo cmd1 bar -x one 8 9'.split()) # Namespace(bar='bar', cmd='cmd1', foo='foo', vars=['8', '9'], x='one') </code></pre>
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    1. COOh this is good news. So are you saying that if I take the two functions you added in http://bugs.python.org/file30422/intermixed.patch and I implement in my own subclass I'll be able to get around the problem? What about the `_get_values()` function, is the two-lines change to it strictly necessary? I find it difficult to understand how `SUPPRESS` is used.
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    2. COOh no, bad news just arrived. I read that this is incompatible with subparsers, a feature I absolutely need. Is that temporary or just impossible to realize? Instinctively I'd say that it should be possible to do, because the subparser is specified as second argument, then the parsing happens normally. Am I wrong?
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    3. COI tried 2 different ways of temporarily disabling the `positional` arguments. The first was `nargs=0`. The second was `nargs=SUPPRESS`. I would use the first if implementing my own subclass. `SUPPRESS` has some advantages but requires deeper changes to `argparse.
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