By adding a py__class__ method to CompiledObject and Class, we Jedi is able to understand isinstance checks, now.

This also includes a CheckAttribute class in evaluatue.compiled, because it's way easier to generalize the AttributeErrors there.

jedi/evaluate/compiled/__init__.py

@@ -5,6 +5,7 @@ import inspect
 import re
 import sys
 import os
+from functools import partial
 
 from jedi._compatibility import builtins as _builtins, unicode
 from jedi import debug
@@ -22,6 +23,19 @@ _path_re = re.compile('(?:\.[^{0}]+|[{0}]__init__\.py)$'.format(re.escape(_sep))
 del _sep
 
 
+class CheckAttribute(object):
+    """Raises an AttributeError if the attribute X isn't available."""
+    def __init__(self, func):
+        self.func = func
+        # Remove the py in front of e.g. py__call__.
+        self.check_name = func.__name__[2:]
+
+    def __get__(self, instance, owner):
+        # This might raise an AttributeError. That's wanted.
+        getattr(instance.obj, self.check_name)
+        return partial(self.func, instance)
+
+
 class CompiledObject(Base):
     # comply with the parser
     start_pos = 0, 0
@@ -45,9 +59,15 @@ class CompiledObject(Base):
         self.obj.__call__
         return actual
 
+    @CheckAttribute
+    def py__class__(self, evaluator):
+        return CompiledObject(self.obj.__class__, parent=self.parent)
+
+    @CheckAttribute
     def py__mro__(self, evaluator):
         return tuple(create(evaluator, cls) for cls in self.obj.__mro__)
 
+    @CheckAttribute
     def py__bases__(self, evaluator):
         return tuple(create(evaluator, cls) for cls in self.obj.__bases__)
 
@@ -55,7 +75,7 @@ class CompiledObject(Base):
         return bool(self.obj)
 
     def is_class(self):
-        return isinstance(self.obj, type)
+        return inspect.isclass(self.obj)
 
     @property
     def doc(self):

jedi/evaluate/representation.py

@@ -110,6 +110,9 @@ class Instance(use_metaclass(CachedMetaClass, Executed)):
 
         return actual
 
+    def py__class__(self, evaluator):
+        return self.base
+
     def py__bool__(self):
         # Signalize that we don't know about the bool type.
         return None

jedi/evaluate/stdlib.py

@@ -140,7 +140,7 @@ def builtins_isinstance(evaluator, obj, params):
     for o in obj:
         for cls in classes:
             try:
-                mro_func = o.base.py__mro__
+                mro_func = o.py__class__(evaluator).py__mro__
             except AttributeError:
                 return any_bool
             else: