Clarified error in read_sas method when buffer object provided without format

Author: tomrod

doc/source/whatsnew/v0.20.0.txt

@@ -271,6 +271,7 @@ Performance Improvements
 - Improved performance of ``pd.wide_to_long()`` (:issue:`14779`)
 - Increased performance of ``pd.factorize()`` by releasing the GIL with ``object`` dtype when inferred as strings (:issue:`14859`)
 
+- When reading buffer object in ``read_sas()`` method without specified format, filepath string is inferred rather than buffer object. Error is now thrown if buffer object is provided without format {sas7bdat|xport} specification.
 
 
 .. _whatsnew_0200.bug_fixes:

pandas/io/sas/sasreader.py

@@ -31,6 +31,9 @@ def read_sas(filepath_or_buffer, format=None, index=None, encoding=None,
     """
 
     if format is None:
+        bufferr = "Format unrecognized. If buffer object, specify format")
+        if type(filesize_or_buffer) != str:
+            raise TypeError(bufferr)
         try:
             fname = filepath_or_buffer.lower()
             if fname.endswith(".xpt"):