begin implementing inspection system for #2208

1 files changed, 44 insertions, 0 deletions

diff --git a/lib/sqlalchemy/inspection.py b/lib/sqlalchemy/inspection.py
new file mode 100644
index 000000000..9ce52beab
--- /dev/null
+++ b/lib/sqlalchemy/inspection.py
@@ -0,0 +1,44 @@
+# sqlalchemy/inspect.py
+# Copyright (C) 2005-2012 the SQLAlchemy authors and contributors <see AUTHORS file>
+#
+# This module is part of SQLAlchemy and is released under
+# the MIT License: http://www.opensource.org/licenses/mit-license.php
+
+"""Base inspect API.
+
+:func:`.inspect` provides access to a contextual object
+regarding a subject.   
+
+Various subsections of SQLAlchemy,
+such as the :class:`.Inspector`, :class:`.Mapper`, and
+others register themselves with the "inspection registry" here
+so that they may return a context object given a certain kind
+of argument.
+"""
+
+from sqlalchemy import util
+_registrars = util.defaultdict(list)
+
+def inspect(subject):
+    type_ = type(subject)
+    for cls in type_.__mro__:
+        if cls in _registrars:
+            reg = _registrars[cls]
+            break
+    else:
+        raise exc.InvalidRequestError(
+                "No inspection system is "
+                "available for object of type %s" % 
+                type_)
+    return reg(subject)
+
+def _inspects(*types):
+    def decorate(fn_or_cls):
+        for type_ in types:
+            if type_ in _registrars:
+                raise AssertionError(
+                            "Type %s is already "
+                            "registered" % type_)
+            _registrars[type_] = fn_or_cls
+        return fn_or_cls
+    return decorate