only infer Optional for func

Author: tharvik

mypy/stubgen.py

@@ -254,7 +254,7 @@ def visit_func_def(self, o: FuncDef) -> None:
             if init_stmt:
                 if kind == ARG_NAMED and '*' not in args:
                     args.append('*')
-                typename = self.get_str_type_of_node(init_stmt.rvalue)
+                typename = self.get_str_type_of_node(init_stmt.rvalue, True)
                 arg = '{}: {} = ...'.format(name, typename)
             elif kind == ARG_STAR:
                 arg = '*%s' % name
@@ -500,7 +500,8 @@ def is_private_name(self, name: str) -> bool:
                                                      '__setstate__',
                                                      '__slots__'))
 
-    def get_str_type_of_node(self, rvalue: Node) -> str:
+    def get_str_type_of_node(self, rvalue: Node,
+                             can_infer_optional: bool = False) -> str:
         if isinstance(rvalue, IntExpr):
             return 'int'
         if isinstance(rvalue, StrExpr):
@@ -513,7 +514,8 @@ def get_str_type_of_node(self, rvalue: Node) -> str:
             return 'int'
         if isinstance(rvalue, NameExpr) and rvalue.name in ('True', 'False'):
             return 'bool'
-        if isinstance(rvalue, NameExpr) and rvalue.name == 'None':
+        if can_infer_optional and \
+           isinstance(rvalue, NameExpr) and rvalue.name == 'None':
             self.add_typing_import('Optional')
             self.add_typing_import('Any')
             return 'Optional[Any]'

test-data/unit/stubgen.test

@@ -543,5 +543,17 @@ def syslog(a): pass
 [out]
 def syslog(a): ...
 
+[case testInferOptionalOnlyFunc]
+class A:
+    x = None
+    def __init__(self, a=None) -> None:
+        self.x = []
+[out]
+from typing import Any, Optional
+
+class A:
+    x = ...  # type: Any
+    def __init__(self, a: Optional[Any] = ...) -> None: ...
+
 -- More features/fixes:
 --   do not export deleted names