Use string_types for string check (elastic#795)

Fixes elastic#792

Author: recursiveMake

elasticsearch_dsl/search.py

@@ -147,7 +147,7 @@ def index(self, *index):
  else:
  indexes = []
  for i in index:
- if isinstance(i, str):
+ if isinstance(i, string_types):
  indexes.append(i)
  elif isinstance(i, list):
  indexes += i

test_elasticsearch_dsl/test_search.py

@@ -162,6 +162,8 @@ def test_search_index():
  assert s._index == ['i']
  s = s.index('i2')
  assert s._index == ['i', 'i2']
+ s = s.index(u'i3')
+ assert s._index == ['i', 'i2', 'i3']
  s = s.index()
  assert s._index is None
  s = search.Search(index=('i', 'i2'))