ENH: return an OrderedDict from read_excel with sheetname=None (pandas-dev#14571)

Author: scls19fr

doc/source/whatsnew/v0.20.0.txt

@@ -30,7 +30,7 @@ New features
 Other enhancements
 ^^^^^^^^^^^^^^^^^^
 
-
+- ``pd.read_excel`` now preserves sheet order when using ``sheetname=None`` (:issue:`9930`)
 
 
 .. _whatsnew_0200.api_breaking:

pandas/io/excel.py

@@ -21,7 +21,7 @@
 from pandas.tseries.period import Period
 from pandas import json
 from pandas.compat import (map, zip, reduce, range, lrange, u, add_metaclass,
-                           string_types)
+                           string_types, OrderedDict)
 from pandas.core import config
 from pandas.formats.printing import pprint_thing
 import pandas.compat as compat
@@ -418,9 +418,9 @@ def _parse_cell(cell_contents, cell_typ):
             sheets = [sheetname]
 
         # handle same-type duplicates.
-        sheets = list(set(sheets))
+        sheets = list(OrderedDict.fromkeys(sheets).keys())
 
-        output = {}
+        output = OrderedDict()
 
         for asheetname in sheets:
             if verbose:

pandas/io/tests/data/test_multisheet.xls

@@ -379,8 +379,12 @@ def test_reading_all_sheets(self):
         # See PR #9450
         basename = 'test_multisheet'
         dfs = self.get_exceldf(basename, sheetname=None)
-        expected_keys = ['Alpha', 'Beta', 'Charlie']
+        # ensure this is not alphabetical to test order preservation
+        expected_keys = ['Charlie', 'Alpha', 'Beta']
         tm.assert_contains_all(expected_keys, dfs.keys())
+        # Issue 9930
+        # Ensure sheet order is preserved
+        tm.assert_equal(expected_keys, list(dfs.keys()))
 
     def test_reading_multiple_specific_sheets(self):
         # Test reading specific sheetnames by specifying a mixed list