BUG: long str unconvert fix

pandas/io/pytables.py

@@ -40,13 +40,15 @@
 import pandas.tslib as tslib
 
 from contextlib import contextmanager
+from distutils.version import LooseVersion
 
 # versioning attribute
 _version = '0.10.1'
 
 # PY3 encoding if we don't specify
 _default_encoding = 'UTF-8'
 
+_np_version_under_172 = LooseVersion(np.__version__) < '1.7.2'
 
 def _ensure_decoded(s):
     """ if we have bytes, decode them to unicde """
@@ -4165,7 +4167,6 @@ def _convert_string_array(data, encoding, itemsize=None):
     data = np.array(data, dtype="S%d" % itemsize)
     return data
 
-
 def _unconvert_string_array(data, nan_rep=None, encoding=None):
     """ deserialize a string array, possibly decoding """
     shape = data.shape
@@ -4175,8 +4176,14 @@ def _unconvert_string_array(data, nan_rep=None, encoding=None):
     # where the passed encoding is actually None)
     encoding = _ensure_encoding(encoding)
     if encoding is not None and len(data):
+        if _np_version_under_172:
+            itemsize = lib.max_len_string_array(data)
+            dtype = (str, itemsize)
+        else:
+            dtype = str
+
         try:
-            data = data.astype(string_types).astype(object)
+            data = data.astype(dtype).astype(object)
         except:
             f = np.vectorize(lambda x: x.decode(encoding), otypes=[np.object])
             data = f(data)

pandas/io/tests/test_pytables.py

@@ -176,6 +176,17 @@ def roundtrip(key, obj,**kwargs):
         finally:
             safe_remove(self.path)
 
+    def test_long_strings(self):
+        df = DataFrame({'a': [tm.rands(100) for _ in range(10)]}, 
+                index=[tm.rands(100) for _ in range(10)])
+
+        with ensure_clean_store(self.path) as store:
+            store.append('df', df, data_columns=['a'])
+
+            result = store.select('df')
+            assert_frame_equal(df, result)
+
+
     def test_api(self):
 
         # GH4584