Move the isinstance checks out of finder

jedi/inference/context.py

@@ -7,6 +7,7 @@ from parso.python.tree import Name
 from jedi.inference.filters import ParserTreeFilter, MergedFilter, \
     GlobalNameFilter
 from jedi.inference.base_value import NO_VALUES
+from jedi.parser_utils import get_parent_scope
 from jedi import debug
 from jedi import parser_utils
 
@@ -80,7 +81,29 @@ class AbstractContext(object):
                 from jedi.inference import analysis
                 message = ("NameError: name '%s' is not defined." % string_name)
                 analysis.add(name_context, 'name-error', name_or_str, message)
-        return values
+        if values:
+            return values
+        return self._check_for_additional_knowledge(name_or_str, name_context, position)
+
+    def _check_for_additional_knowledge(self, name_or_str, name_context, position):
+        name_context = name_context or self
+        # Add isinstance and other if/assert knowledge.
+        if isinstance(name_or_str, Name) and not name_context.is_instance():
+            flow_scope = name_or_str
+            base_nodes = [name_context.tree_node]
+
+            if any(b.type in ('comp_for', 'sync_comp_for') for b in base_nodes):
+                return NO_VALUES
+            from jedi.inference.finder import check_flow_information
+            while True:
+                flow_scope = get_parent_scope(flow_scope, include_flows=True)
+                n = check_flow_information(name_context, flow_scope,
+                                           name_or_str, position)
+                if n is not None:
+                    return n
+                if flow_scope in base_nodes:
+                    break
+        return NO_VALUES
 
     def get_root_context(self):
         parent_context = self.parent_context