refactor issubclass check into helper function

Author: TH3CHARLie

mypy/checker.py

@@ -3726,35 +3726,7 @@ def find_isinstance_check(self, node: Expression
             elif refers_to_fullname(node.callee, 'builtins.issubclass'):
                 if len(node.args) != 2:  # the error will be reported elsewhere
                     return {}, {}
-                expr = node.args[0]
-                if literal(expr) == LITERAL_TYPE:
-                    vartype = get_proper_type(type_map[expr])
-                    type = get_isinstance_type(node.args[1], type_map)
-                    if (isinstance(vartype, TypeVarType)):
-                        vartype = vartype.upper_bound
-                    vartype = get_proper_type(vartype)
-                    if isinstance(vartype, UnionType):
-                        union_list = []
-                        for t in get_proper_types(vartype.items):
-                            if isinstance(t, TypeType):
-                                union_list.append(t.item)
-                            else:
-                                # This is an error that should be reported earlier
-                                # if we reach here, we refuse to do any type inference.
-                                return {}, {}
-                        vartype = UnionType(union_list)
-                    elif isinstance(vartype, TypeType):
-                        vartype = vartype.item
-                    elif (isinstance(vartype, Instance) and
-                            vartype.type.fullname() == 'builtins.type'):
-                        vartype = self.named_type('builtins.object')
-                    else:
-                        # Any other object whose type we don't know precisely
-                        # for example, Any or a custom metaclass.
-                        return {}, {}  # unknown type
-                    yes_map, no_map = conditional_type_map(expr, vartype, type)
-                    yes_map, no_map = map(convert_to_typetype, (yes_map, no_map))
-                    return yes_map, no_map
+                return self.infer_issubclass_maps(node, type_map)
             elif refers_to_fullname(node.callee, 'builtins.callable'):
                 if len(node.args) != 1:  # the error will be reported elsewhere
                     return {}, {}
@@ -4197,6 +4169,40 @@ def push_type_map(self, type_map: 'TypeMap') -> None:
             for expr, type in type_map.items():
                 self.binder.put(expr, type)
 
+    def infer_issubclass_maps(self, node: CallExpr,
+                              type_map: Dict[Expression, Type]
+                              ) -> Tuple[TypeMap, TypeMap]:
+        expr = node.args[0]
+        if literal(expr) == LITERAL_TYPE:
+            vartype = type_map[expr]
+            type = get_isinstance_type(node.args[1], type_map)
+            if (isinstance(vartype, TypeVarType)):
+                vartype = vartype.upper_bound
+            vartype = get_proper_type(vartype)
+            if isinstance(vartype, UnionType):
+                union_list = []
+                for t in get_proper_types(vartype.items):
+                    if isinstance(t, TypeType):
+                        union_list.append(t.item)
+                    else:
+                        # This is an error that should be reported earlier
+                        # if we reach here, we refuse to do any type inference.
+                        return {}, {}
+                vartype = UnionType(union_list)
+            elif isinstance(vartype, TypeType):
+                vartype = vartype.item
+            elif (isinstance(vartype, Instance) and
+                    vartype.type.fullname() == 'builtins.type'):
+                vartype = self.named_type('builtins.object')
+            else:
+                # Any other object whose type we don't know precisely
+                # for example, Any or a custom metaclass.
+                return {}, {}  # unknown type
+            yes_map, no_map = conditional_type_map(expr, vartype, type)
+            yes_map, no_map = map(convert_to_typetype, (yes_map, no_map))
+            return yes_map, no_map
+        return {}, {}
+
 
 def conditional_type_map(expr: Expression,
                          current_type: Optional[Type],