allow path to be an StringIO object and skip extension check for that case

pandas/io/excel.py

@@ -18,6 +18,7 @@
 import pandas.compat as compat
 import pandas.core.common as com
 from warnings import warn
+from StringIO import StringIO
 
 __all__ = ["read_excel", "ExcelWriter", "ExcelFile"]
 
@@ -431,8 +432,9 @@ def save(self):
 
     def __init__(self, path, engine=None, **engine_kwargs):
         # validate that this engine can handle the extnesion
-        ext = os.path.splitext(path)[-1]
-        self.check_extension(ext)
+        if not isinstance(path, StringIO):
+            ext = os.path.splitext(path)[-1]
+            self.check_extension(ext)
 
         self.path = path
         self.sheets = {}

pandas/io/tests/test_excel.py

@@ -17,6 +17,7 @@
 )
 from pandas.util.testing import ensure_clean
 from pandas.core.config import set_option, get_option
+from StringIO import StringIO
 import pandas.util.testing as tm
 import pandas as pd
 
@@ -410,6 +411,22 @@ def test_excelwriter_contextmanager(self):
                 tm.assert_frame_equal(found_df, self.frame)
                 tm.assert_frame_equal(found_df2, self.frame2)
 
+    def test_stringio_writer(self):
+        _skip_if_no_xlsxwriter()
+        _skip_if_no_xlrd()
+
+        path = StringIO()
+        with ExcelWriter(path, engine='xlsxwriter', **{'options': {'in-memory': True}}) as ew:
+            self.frame.to_excel(ew, 'test1', engine='xlsxwriter')
+            ew.save()
+            path.seek(0)
+            ef = ExcelFile(path)
+            found_df = ef.parse('test1')
+            tm.assert_frame_equal(self.frame, found_df)
+        path.close()
+
+
+
     def test_roundtrip(self):
         _skip_if_no_xlrd()