Make params work with access

jedi/evaluate/compiled/access.py

@@ -1,8 +1,9 @@
 import inspect
 import types
 import operator as op
+from collections import namedtuple
 
-from jedi._compatibility import unicode, is_py3, is_py34, builtins
+from jedi._compatibility import unicode, is_py3, is_py34, builtins, py_version
 from jedi.evaluate.compiled.getattr_static import getattr_static
 
 
@@ -72,6 +73,7 @@ _OPERATORS = {
 _OPERATORS.update(COMPARISON_OPERATORS)
 
 
+SignatureParam = namedtuple('SignatureParam', 'name default empty annotation')
 
 
 class DirectObjectAccess(object):
@@ -142,6 +144,9 @@ class DirectObjectAccess(object):
     def is_class(self):
         return inspect.isclass(self._obj)
 
+    def ismethoddescriptor(self):
+        return inspect.ismethoddescriptor(self._obj)
+
     def dir(self):
         return dir(self._obj)
 
@@ -242,6 +247,36 @@ class DirectObjectAccess(object):
     def needs_type_completions(self):
         return inspect.isclass(self._obj) and self._obj != type
 
+    def get_signature_params(self):
+        obj = self._obj
+        if py_version < 33:
+            raise ValueError("inspect.signature was introduced in 3.3")
+        if py_version == 34:
+            # In 3.4 inspect.signature are wrong for str and int. This has
+            # been fixed in 3.5. The signature of object is returned,
+            # because no signature was found for str. Here we imitate 3.5
+            # logic and just ignore the signature if the magic methods
+            # don't match object.
+            # 3.3 doesn't even have the logic and returns nothing for str
+            # and classes that inherit from object.
+            user_def = inspect._signature_get_user_defined_method
+            if (inspect.isclass(obj)
+                    and not user_def(type(obj), '__init__')
+                    and not user_def(type(obj), '__new__')
+                    and (obj.__init__ != object.__init__
+                         or obj.__new__ != object.__new__)):
+                raise ValueError
+
+        signature = inspect.signature(obj)
+        return [
+            SignatureParam(
+                name=p.name,
+                default=p.default,
+                empty=p.empty,
+                annotation=p.annotation,
+            ) for p in signature.parameters
+        ]
+
 
 def is_class_instance(obj):
     """Like inspect.* methods."""