Correct argparse behavior

- disallow zero args
- print help message if no commands given

client/cli/bam

@@ -108,7 +108,7 @@ class bam_utils:
                 stream=True,
                 )
 
-        if r.status_code not in {200,}:
+        if r.status_code not in {200, }:
             # TODO(cam), make into reusable function?
             print("Error %d:\n%s" % (r.status_code, next(r.iter_content(chunk_size=1024)).decode('utf-8')))
             return
@@ -186,7 +186,7 @@ def subcommand_status_cb(args):
 def create_argparse_checkout(subparsers):
     subparse = subparsers.add_parser("checkout", aliases=("co",))
     subparse.add_argument(
-            "paths", nargs="*", help="Path(s) to operate on",
+            "paths", nargs="+", help="Path(s) to operate on",
             )
     subparse.set_defaults(func=subcommand_checkout_cb)
 
@@ -199,7 +199,7 @@ def create_argparse_commit(subparsers):
             help="Commit message",
             )
     subparse.add_argument(
-            "paths", nargs="*", help="paths to commit",
+            "paths", nargs="+", help="paths to commit",
             )
 
     subparse.set_defaults(func=subcommand_commit_cb)
@@ -208,7 +208,7 @@ def create_argparse_commit(subparsers):
 def create_argparse_update(subparsers):
     subparse = subparsers.add_parser("update", aliases=("up",))
     subparse.add_argument(
-            "paths", nargs="*", help="Path(s) to operate on",
+            "paths", nargs="+", help="Path(s) to operate on",
             )
     subparse.set_defaults(func=subcommand_update_cb)
 
@@ -216,7 +216,7 @@ def create_argparse_update(subparsers):
 def create_argparse_revert(subparsers):
     subparse = subparsers.add_parser("update", aliases=("up",))
     subparse.add_argument(
-            "paths", nargs="*", help="Path(s) to operate on",
+            "paths", nargs="+", help="Path(s) to operate on",
             )
     subparse.set_defaults(func=subcommand_revert_cb)
 
@@ -225,7 +225,7 @@ def create_argparse_revert(subparsers):
 def create_argparse_status(subparsers):
     subparse = subparsers.add_parser("status", aliases=("st",))
     subparse.add_argument(
-            "paths", nargs="*", help="Path(s) to operate on",
+            "paths", nargs="+", help="Path(s) to operate on",
             )
     subparse.set_defaults(func=subcommand_status_cb)
 
@@ -233,7 +233,7 @@ def create_argparse_status(subparsers):
 def create_argparse_list(subparsers):
     subparse = subparsers.add_parser("list", aliases=("ls",))
     subparse.add_argument(
-            "paths", nargs="*", help="Path(s) to operate on",
+            "paths", nargs="+", help="Path(s) to operate on",
             )
     subparse.set_defaults(func=subcommand_list_cb)
 
@@ -273,6 +273,10 @@ def main():
     args = parser.parse_args(sys.argv[1:])
 
     # call subparser callback
+    if not hasattr(args, "func"):
+        parser.print_help()
+        return
+
     args.func(args)