Add helpers.is_supertype and helpers.is_subtype, two functions for checking if an object is a super/sub type of another.

1 files changed, 77 insertions, 16 deletions

diff --git a/astroid/helpers.py b/astroid/helpers.py
index 5996c7c7..fa941d94 100644
--- a/astroid/helpers.py
+++ b/astroid/helpers.py
@@ -1,19 +1,19 @@
-# copyright 2003-2015 LOGILAB S.A. (Paris, FRANCE), all rights reserved.
-# contact http://www.logilab.fr/ -- mailto:contact@logilab.fr
-#
-# This file is part of astroid.
-#
-# astroid is free software: you can redistribute it and/or modify it
-# under the terms of the GNU Lesser General Public License as published by the
-# Free Software Foundation, either version 2.1 of the License, or (at your
-# option) any later version.
-#
-# astroid is distributed in the hope that it will be useful, but
-# WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
-# FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public License
-# for more details.
-#
-# You should have received a copy of the GNU Lesser General Public License along
+# copyright 2003-2015 LOGILAB S.A. (Paris, FRANCE), all rights reserved.

+# contact http://www.logilab.fr/ -- mailto:contact@logilab.fr

+#

+# This file is part of astroid.

+#

+# astroid is free software: you can redistribute it and/or modify it

+# under the terms of the GNU Lesser General Public License as published by the

+# Free Software Foundation, either version 2.1 of the License, or (at your

+# option) any later version.

+#

+# astroid is distributed in the hope that it will be useful, but

+# WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

+# FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public License

+# for more details.

+#

+# You should have received a copy of the GNU Lesser General Public License along

 # with astroid. If not, see <http://www.gnu.org/licenses/>.

 

 """

@@ -93,3 +93,64 @@ def object_type(node, context=None):
     if len(types) > 1:

         return bases.YES

     return list(types)[0]

+

+

+def safe_infer(node, context=None):

+    """Return the inferred value for the given node.

+

+    Return None if inference failed or if there is some ambiguity (more than

+    one node has been inferred).

+    """

+    try:

+        inferit = node.infer(context=context)

+        value = next(inferit)

+    except exceptions.InferenceError:

+        return

+    try:

+        next(inferit)

+        return # None if there is ambiguity on the inferred node

+    except exceptions.InferenceError:

+        return # there is some kind of ambiguity

+    except StopIteration:

+        return value

+

+

+def has_known_bases(klass, context=None):

+    """Return true if all base classes of a class could be inferred."""

+    try:

+        return klass._all_bases_known

+    except AttributeError:

+        pass

+    for base in klass.bases:

+        result = safe_infer(base, context=context)

+        # TODO: check for A->B->A->B pattern in class structure too?

+        if (not isinstance(result, scoped_nodes.Class) or

+                result is klass or

+                not has_known_bases(result, context=context)):

+            klass._all_bases_known = False

+            return False

+    klass._all_bases_known = True

+    return True

+

+

+def _type_check(type1, type2):

+    if not all(map(has_known_bases, (type1, type2))):

+        return bases.YES

+

+    if not all([type1.newstyle, type2.newstyle]):

+        return False

+    try:

+        return type1 in type2.mro()[:-1]

+    except exceptions.MroError:

+        # The MRO is invalid.

+        return bases.YES

+

+

+def is_subtype(type1, type2):

+    """Check if *type1* is a subtype of *typ2*."""

+    return _type_check(type2, type1)

+

+

+def is_supertype(type1, type2):

+    """Check if *type2* is a supertype of *type1*."""

+    return _type_check(type1, type2)