Make partial use the __doc__ of its function, fixes #1621

jedi/inference/gradual/conversion.py

@@ -18,6 +18,7 @@ def _stub_to_python_value_set(stub_value, ignore_compiled=False):
 
     was_instance = stub_value.is_instance()
     if was_instance:
+        arguments = getattr(stub_value, '_arguments', None)
         stub_value = stub_value.py__class__()
 
     qualified_names = stub_value.get_qualified_names()
@@ -30,11 +31,12 @@ def _stub_to_python_value_set(stub_value, ignore_compiled=False):
         method_name = qualified_names[-1]
         qualified_names = qualified_names[:-1]
         was_instance = True
+        arguments = None
 
     values = _infer_from_stub(stub_module_context, qualified_names, ignore_compiled)
     if was_instance:
         values = ValueSet.from_sets(
-            c.execute_with_values()
+            c.execute_with_values() if arguments is None else c.execute(arguments)
             for c in values
             if c.is_class()
         )

jedi/plugins/stdlib.py

@@ -474,11 +474,10 @@ def collections_namedtuple(value, arguments, callback):
 class PartialObject(ValueWrapper):
     def __init__(self, actual_value, arguments, instance=None):
         super(PartialObject, self).__init__(actual_value)
-        self._actual_value = actual_value
         self._arguments = arguments
         self._instance = instance
 
-    def _get_function(self, unpacked_arguments):
+    def _get_functions(self, unpacked_arguments):
         key, lazy_value = next(unpacked_arguments, (None, None))
         if key is not None or lazy_value is None:
             debug.warning("Partial should have a proper function %s", self._arguments)
@@ -487,8 +486,8 @@ class PartialObject(ValueWrapper):
 
     def get_signatures(self):
         unpacked_arguments = self._arguments.unpack()
-        func = self._get_function(unpacked_arguments)
-        if func is None:
+        funcs = self._get_functions(unpacked_arguments)
+        if funcs is None:
             return []
 
         arg_count = 0
@@ -500,17 +499,30 @@ class PartialObject(ValueWrapper):
                 arg_count += 1
             else:
                 keys.add(key)
-        return [PartialSignature(s, arg_count, keys) for s in func.get_signatures()]
+        return [PartialSignature(s, arg_count, keys) for s in funcs.get_signatures()]
 
     def py__call__(self, arguments):
-        func = self._get_function(self._arguments.unpack())
-        if func is None:
+        funcs = self._get_functions(self._arguments.unpack())
+        if funcs is None:
             return NO_VALUES
 
-        return func.execute(
+        return funcs.execute(
             MergedPartialArguments(self._arguments, arguments, self._instance)
         )
 
+    def py__doc__(self):
+        """
+        In CPython partial does not replace the docstring. However we are still
+        imitating it here, because we want this docstring to be worth something
+        for the user.
+        """
+        callables = self._get_functions(self._arguments.unpack())
+        if callables is None:
+            return ''
+        for callable_ in callables:
+            return callable_.py__doc__()
+        return ''
+
     def py__get__(self, instance, class_value):
         return ValueSet([self])
 
@@ -519,7 +531,7 @@ class PartialMethodObject(PartialObject):
     def py__get__(self, instance, class_value):
         if instance is None:
             return ValueSet([self])
-        return ValueSet([PartialObject(self._actual_value, self._arguments, instance)])
+        return ValueSet([PartialObject(self._wrapped_value, self._arguments, instance)])
 
 
 class PartialSignature(SignatureWrapper):

test/test_inference/test_docstring.py

@@ -422,6 +422,19 @@ def test_decorator(Script):
     assert d.docstring(raw=True) == 'Nice docstring'
 
 
+def test_partial(Script):
+    code = dedent('''
+        def foo():
+            'x y z'
+        from functools import partial
+        x = partial(foo)
+        x''')
+
+    p1, p2 = Script(code).infer()
+    assert p1.docstring(raw=True) == 'x y z'
+    assert p2.docstring(raw=True) == 'x y z'
+
+
 def test_basic_str_init_signature(Script, disable_typeshed):
     # See GH #1414 and GH #1426
     code = dedent('''