Create _CompletingAction and add to parser explicitly so the --_completion option shows up in help and command completion

Author: dbarnett

README

@@ -40,10 +40,12 @@ prog.py:
 
 $ chmod +x prog.py
 $ ./prog.py <TAB><TAB>
-0        2        4        6        8        -h       --sum
-1        3        5        7        9        --help
+0               4               8               --help
+1               5               9               --sum
+2               6               --_completion   
+3               7               -h              
 $ ./prog.py -<TAB><TAB>
--h       --help   --sum
+--_completion   -h              --help          --sum
 $ ./prog.py 1<TAB><TAB>
 0  1  2  3  4  5  6  7  8  9
 

selfcompletion/__init__.py

@@ -1,26 +1,37 @@
 import argparse
 import re
 
-class SelfCompletingArgumentParser(argparse.ArgumentParser):
-    def __init__(self, *args, **kw):
-        argparse.ArgumentParser.__init__(self, *args, **kw)
-        self._completion_parser = argparse.ArgumentParser()
-        self._completion_parser.add_argument('--_completion', type=str)
+class _CompletionAction(argparse.Action):
+    def __init__(self,
+                 option_strings,
+                 dest='_completion',
+                 metavar='CMD_LINE',
+                 default=argparse.SUPPRESS,
+                 help="Built-in command completion"):
+        super(_CompletionAction, self).__init__(
+            option_strings=option_strings,
+            dest=dest,
+            metavar=metavar,
+            default=default,
+            nargs=1,
+            type=str,
+            help=help)
 
-    def parse_args(self, *args, **kw):
-        comp_args = self._completion_parser.parse_args(*args, **kw)
-        if comp_args._completion is not None:
-            comp_words = re.split(r'\s+', comp_args._completion)
-            comp_word = comp_words[-1]
-            all_options = sum((a.option_strings for a in self._actions), [])
-            types = [a.type for a in self._actions if a.nargs != 0 and a.type is not None]
-            for opt in all_options:
-                if opt.startswith(comp_word):
-                    print opt+' '
-            if int in types and re.match(r'^\d*$', comp_word):
-                for i in xrange(10):
-                    print i
+    def __call__(self, parser, namespace, values, option_string=None):
+        comp_words = re.split(r'\s+', values[0])
+        comp_word = comp_words[-1]
+        all_options = sum((a.option_strings for a in parser._actions), [])
+        types = [a.type for a in parser._actions if a.nargs != 0 and a.type is not None]
+        for opt in all_options:
+            if opt.startswith(comp_word):
+                print opt+' '
+        if int in types and re.match(r'^\d*$', comp_word):
+            for i in xrange(10):
+                print i
+        parser.exit()
 
-            self.exit(0)
-        else:
-            return argparse.ArgumentParser.parse_args(self, *args, **kw)
+class SelfCompletingArgumentParser(argparse.ArgumentParser):
+    def __init__(self, *args, **kw):
+        super(SelfCompletingArgumentParser, self).__init__(*args, **kw)
+        completion_action = _CompletionAction(['--_completion'])
+        self._add_action(completion_action)