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copied!<p>A solution consists in subclassing <code>argparse.ArgumentParser</code> and redefining its <code>error()</code> method. In fact, upon error, <code>ArgumentParser</code> calls its <code>error()</code> method. The custom argument parsing can then be performed through the subclass instead of <code>argparse.ArgumentParser</code>. A model <code>error()</code> function is found in the source for <code>argparse</code>:</p> <pre><code>def error(self, message): """error(message: string) Prints a usage message incorporating the message to stderr and exits. If you override this in a subclass, it should not return -- it should either exit or raise an exception. """ self.print_usage(sys.stderr) self.exit(2, '%s: error: %s\n' % (self.prog, message)) </code></pre> <p>It is for instance possible to raise an exception in <code>error()</code>, instead of printing a message, so that the code calling <code>parse_args()</code> takes charge of problems with the user parameters.</p> <p><strong>Original answer</strong>: according to the clarification in the comments, the following does not work. However, it provides a mechanism for accessing help messages from the sub-command functions:</p> <p>You almost have it: in each of your <code>*_command(args)</code> functions, you can test the size of <code>args</code> and print an error message if there are not enough arguments.</p> <p>If you want to use the automatically generated help, in your command functions, you can get it by passing the subparsers to each command, like so:</p> <pre><code>args.command(subparsers, args) # Instead of args.command(args) </code></pre> <p>Each <code>*_command()</code> function should then simply take two arguments instead of one. The automatically generated help is accessible through:</p> <pre><code>subparsers.choices['beaker'].print_help() # or print_usage() </code></pre> <p>for instance.</p> <p>You could alternatively choose to directly pass the particular subparser to each sub-command routine <code>*_command()</code>:</p> <pre><code>args.command(subparsers.choices[sys.argv[1]], args) </code></pre> <p>and then, in each <code>*_command(subparser, args)</code>, print the help with <code>subparser.print_help()</code>.</p>

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