Add command to display tags

CHANGES.rst

@@ -41,6 +41,8 @@
 - Added a diff tool to ``asdftool`` to allow for visual comparison of pairs of
   ASDF files. [#286]
 
+- Added command to ``asdftool`` to display available tags. [#303]
+
 
 1.2.1(2016-11-07)
 -----------------

asdf/commands/__init__.py

@@ -7,3 +7,4 @@
 from .to_yaml import *
 from .defragment import *
 from .diff import *
+from .tags import *

asdf/commands/tags.py

@@ -0,0 +1,52 @@
+# Licensed under a 3-clause BSD style license - see LICENSE.rst
+# -*- coding: utf-8 -*-
+
+"""
+Implementation of command for displaying available tags in asdf
+"""
+
+from __future__ import absolute_import, division, unicode_literals, print_function
+
+import sys
+
+from .main import Command
+from .. import AsdfFile
+
+
+__all__ = ['list_tags']
+
+
+class TagLister(Command): # pragma: no cover
+    """This class is the plugin implementation for the asdftool runner."""
+    @classmethod
+    def setup_arguments(cls, subparsers):
+        parser = subparsers.add_parser(
+            str("tags"), help="List currently available tags",
+            description="""Lists currently available tags.""")
+
+        parser.add_argument(
+            '-d', '--display-classes', action='store_true',
+            help="""Display associated class names in addition to tags""")
+
+        parser.set_defaults(func=cls.run)
+
+        return parser
+
+    @classmethod
+    def run(cls, args):
+        return list_tags(display_classes=args.display_classes)
+
+def _qualified_name(_class):
+    return "{}.{}".format(_class.__module__, _class.__name__)
+
+def list_tags(display_classes=False, iostream=sys.stdout):
+    """Function to list tags"""
+    af = AsdfFile()
+    type_by_tag = af._extensions._type_index._type_by_tag
+    tags = sorted(type_by_tag.keys())
+
+    for tag in tags:
+        string = str(tag)
+        if display_classes:
+            string += ":  " + _qualified_name(type_by_tag[tag])
+        iostream.write(string + '\n')

asdf/commands/tests/test_tags.py

@@ -0,0 +1,41 @@
+# Licensed under a 3-clause BSD style license - see LICENSE.rst
+# -*- coding: utf-8 -*-
+
+from __future__ import absolute_import, division, unicode_literals, print_function
+
+import io
+
+from ... import AsdfFile
+from .. import list_tags
+
+def _get_tags(display_classes):
+    iostream = io.StringIO()
+    list_tags(display_classes=display_classes, iostream=iostream)
+    iostream.seek(0)
+    return [line.strip() for line in iostream.readlines()]
+
+def _class_to_string(_class):
+    return "{}.{}".format(_class.__module__, _class.__name__)
+
+def test_list_schemas():
+    obs_tags = _get_tags(False)
+
+    af = AsdfFile()
+    exp_tags = sorted(af._extensions._type_index._type_by_tag.keys())
+
+    for exp, obs in zip(exp_tags, obs_tags):
+        assert exp == obs
+
+def test_list_schemas_and_tags():
+    tag_lines = _get_tags(True)
+
+    af = AsdfFile()
+    type_by_tag = af._extensions._type_index._type_by_tag
+    exp_tags = sorted(type_by_tag.keys())
+
+    for exp_tag, line in zip(exp_tags, tag_lines):
+        tag_name, tag_class = line.split(":  ")
+        assert tag_name == exp_tag
+
+        exp_class = _class_to_string(type_by_tag[exp_tag])
+        assert tag_class == exp_class