Fix an issue in referencing multidimensional columns by names with di…

…ct notation

datamatrix/_datamatrix/_datamatrix.py

@@ -343,6 +343,8 @@ def _slice(self, key):
         # and row. Therefore, we turn tuples into lists.
         if isinstance(key, tuple):
             key = list(key)
+            if isinstance(key[0], str):
+                return self._getcolbyname(key[0])[key[1:]]
         _rowid = self._rowid[key]
         dm = DataMatrix(len(_rowid))
         object.__setattr__(dm, u'_rowid', _rowid)

datamatrix/_datamatrix/_multidimensionalcolumn.py

@@ -23,10 +23,7 @@
 from datamatrix import cfg
 from datamatrix._datamatrix._numericcolumn import NumericColumn, FloatColumn
 from datamatrix._datamatrix._datamatrix import DataMatrix
-try:
-    from collections.abc import Sequence  # Python 3.3 and later
-except ImportError:
-    from collections import Sequence
+from collections.abc import Sequence, Collection
 from collections import OrderedDict
 try:
     import numpy as np
@@ -103,7 +100,9 @@ def __init__(self, datamatrix, shape, defaultnan=True, **kwargs):
                 normshape += (dim_size, )
                 self.index_names.append(list(range(dim_size)))
                 self.index_values.append(list(range(dim_size)))
-            else:
+            elif isinstance(dim_size, Collection):
+                if isinstance(dim_size, str):
+                    raise ValueError('A dimension cannot be a string')
                 normshape += (len(dim_size), )
                 self.index_names.append(list(dim_size))
                 self.index_values.append(list(range(len(dim_size))))
@@ -417,7 +416,7 @@ def _getintkey(self, key):
 
     def __getitem__(self, key):
         touch_history.touch(self, try_to_load=True)
-        if isinstance(key, tuple) and len(key) <= len(self._seq.shape):
+        if isinstance(key, (tuple, list)) and len(key) <= len(self._seq.shape):
             # Advanced indexing always returns a copy, rather than a view, so
             # there's no need to explicitly copy the result.
             indices = self._numindices(key, accept_ellipsis=True)