Clarified error in read_sas method when buffer object provided withou…

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.
 
 
 .. _whatsnew_0200.bug_fixes:

pandas/io/sas/sasreader.py

@@ -1,10 +1,12 @@
 """
 Read SAS sas7bdat or xport files.
 """
+from pandas import compat
 
 
 def read_sas(filepath_or_buffer, format=None, index=None, encoding=None,
              chunksize=None, iterator=False):
+
     """
     Read SAS files stored as either XPORT or SAS7BDAT format files.
 
@@ -29,8 +31,12 @@ def read_sas(filepath_or_buffer, format=None, index=None, encoding=None,
     DataFrame if iterator=False and chunksize=None, else SAS7BDATReader
     or XportReader
     """
-
     if format is None:
+        buffer_error_msg = ("If this is a buffer object rather"
+                            "than a string name, you must specify"
+                            " a format string")
+        if not isinstance(filepath_or_buffer, compat.string_types):
+            raise TypeError(buffer_error_msg)
         try:
             fname = filepath_or_buffer.lower()
             if fname.endswith(".xpt"):

pandas/io/tests/sas/test_sas.py

@@ -0,0 +1,11 @@
+import pandas.util.testing as tm
+from pandas.compat import StringIO
+from pandas import read_sas
+
+
+class TestSas(tm.TestCase):
+
+    def test_sas_buffer_format(self):
+        b = StringIO("")
+        with self.assertRaises(TypeError):
+            read_sas(b)