TYP: type annotations for read_sas (#34697)

Author: simonjayhawkins

pandas/io/sas/sasreader.py

@@ -1,11 +1,16 @@
 """
 Read SAS sas7bdat or xport files.
 """
-
 from abc import ABCMeta, abstractmethod
+from typing import TYPE_CHECKING, Optional, Union, overload
+
+from pandas._typing import FilePathOrBuffer, Label
 
 from pandas.io.common import stringify_path
 
+if TYPE_CHECKING:
+    from pandas import DataFrame  # noqa: F401
+
 
 # TODO(PY38): replace with Protocol in Python 3.8
 class ReaderBase(metaclass=ABCMeta):
@@ -22,14 +27,38 @@ def close(self):
         pass
 
 
+@overload
+def read_sas(
+    filepath_or_buffer: FilePathOrBuffer,
+    format: Optional[str] = ...,
+    index: Optional[Label] = ...,
+    encoding: Optional[str] = ...,
+    chunksize: int = ...,
+    iterator: bool = ...,
+) -> ReaderBase:
+    ...
+
+
+@overload
+def read_sas(
+    filepath_or_buffer: FilePathOrBuffer,
+    format: Optional[str] = ...,
+    index: Optional[Label] = ...,
+    encoding: Optional[str] = ...,
+    chunksize: None = ...,
+    iterator: bool = ...,
+) -> Union["DataFrame", ReaderBase]:
+    ...
+
+
 def read_sas(
-    filepath_or_buffer,
-    format=None,
-    index=None,
-    encoding=None,
-    chunksize=None,
-    iterator=False,
-):
+    filepath_or_buffer: FilePathOrBuffer,
+    format: Optional[str] = None,
+    index: Optional[Label] = None,
+    encoding: Optional[str] = None,
+    chunksize: Optional[int] = None,
+    iterator: bool = False,
+) -> Union["DataFrame", ReaderBase]:
     """
     Read SAS files stored as either XPORT or SAS7BDAT format files.