Separate subcommand parsing from subcommand main

Each subcommand implements a create_subcmd_parsers() function that
receives the parent parser and adds its own parsing subcommands and
options.

The main() function of each subcommand receives the top level parsed
'args' object and uses it as it did previously.

Old subcommand main() flow:
1. Define parser
2. Define subparsers
3. Parse args
4. Use args to call functions and pass args.

New top-level command main() flow:
1. Define top level parser
2. Define subcommand names
3. Pass subcommand parser to each subcommand
   'create_subcommand_parsers()'
  3.1 Each subcommand defines its subparser
4. Parse args
5. Use args to call subcommand and pass args to subcommand main()
  5.1 Subcommand main() uses args to call appropriate function and
    validate options.

nixio/cmd/main.py

@@ -20,13 +20,16 @@ def main():
                                     dest="cmd")
 
     # nixio explore
-    subcmds.add_parser("explore", help=explore.__doc__)
+    explore_cmd = subcmds.add_parser("explore", help=explore.__doc__)
+    explore.create_subcmd_parsers(explore_cmd)
 
     # nixio validate
-    subcmds.add_parser("validate", help=validate.__doc__)
+    validate_cmd = subcmds.add_parser("validate", help=validate.__doc__)
+    validate.create_subcmd_parser(validate_cmd)
 
     # nixio upgrade
-    subcmds.add_parser("upgrade", help=upgrade.__doc__)
+    upgrade_cmd = subcmds.add_parser("upgrade", help=upgrade.__doc__)
+    upgrade.create_subcmd_parser(upgrade_cmd)
 
     cmdmap = {
         "explore": explore.main,

nixio/cmd/nixexplore.py

@@ -652,13 +652,10 @@ def create_file_parser(parent_parser):
     file_parser.set_defaults(func=file_worker)
 
 
-def create_parser():
-    parser = argparse.ArgumentParser(prog="nixio-explore",
-                                     description=general_help)
+def create_subcmd_parsers(parser):
     subparsers = parser.add_subparsers(title="commands",
                                        help="Sub commands for working on data and metadata",
-                                       description=tool_description, dest="func")
-
+                                       description=tool_description, dest="explore_cmd")
     create_file_parser(subparsers)
     create_data_parser(subparsers)
     create_dump_parser(subparsers)
@@ -668,14 +665,5 @@ def create_parser():
     return parser
 
 
-def main():
-    parser = create_parser()
-    args = parser.parse_args()
-    if not args.func:
-        parser.print_help()
-        sys.exit(1)
+def main(args):
     args.func(args)
-
-
-if __name__ == "__main__":
-    main()

nixio/cmd/upgrade.py

@@ -249,15 +249,15 @@ def collect_tasks(fname):
     return tasks
 
 
-def main():
-    parser = argparse.ArgumentParser(
-        description="Upgrade NIX files to newest version"
-    )
+def create_subcmd_parser(parser):
     parser.add_argument("-f", "--force", action="store_true",
                         help="overwrite existing files without prompting")
     parser.add_argument("file", type=str, nargs="+",
                         help="path to file to upgrade (at least one)")
-    args = parser.parse_args()
+    return parser
+
+
+def main(args):
     filenames = args.file
 
     tasks = dict()
@@ -297,7 +297,3 @@ def main():
             for task in tasklist:
                 task()
             print("done")
-
-
-if __name__ == "__main__":
-    main()

nixio/cmd/validate.py

@@ -40,21 +40,16 @@ def validate(filename):
     print()
 
 
-def main():
-    parser = argparse.ArgumentParser(
-        description="Validate NIX files"
-    )
-    parser.add_argument("file", type=str, nargs="+",
-                        help="path to file to validate (at least one)")
-    args = parser.parse_args()
+def create_subcmd_parser(parser):
+    return parser.add_argument("file", type=str, nargs="+",
+                               help="path to file to validate (at least one)")
+
+
+def main(args):
     filenames = args.file
 
     for nixfn in filenames:
         if os.path.exists(nixfn):
             validate(nixfn)
         else:
             print("error: No such file '{}'".format(nixfn))
-
-
-if __name__ == "__main__":
-    main()