cannot create a Pattern with selectors containing different numbers of levels

[lebedov]

With c5b56bd, attempting to run the following results in an exception:

import nk.pattern
pat = nk.pattern.Pattern('/a/b','/x/y/z')

Error trace:

/home/lev/Work/projects/bionet/python/nk1/neurokernel/pattern.pyc in __init__(self, *selectors, **kwargs)
   1078         # consecutively:
   1079         for i, s in enumerate(selectors):
-> 1080             self.interface[s, 'interface'] = i
   1081 
   1082         # Create a MultiIndex that can store mappings between identifiers in the

/home/lev/Work/projects/bionet/python/nk1/neurokernel/pattern.pyc in __setitem__(self, key, value)
    181                                       len(self.index.shape))
    182         for k, v in data.iteritems():
--> 183             self.data[k].ix[s] = v
    184 
    185     @property

/home/lev/Work/miniconda/envs/NK1/lib/python2.7/site-packages/pandas/core/indexing.pyc in __setitem__(self, key, value)
    112 
    113     def __setitem__(self, key, value):
--> 114         indexer = self._get_setitem_indexer(key)
    115         self._setitem_with_indexer(indexer, value)
    116 

/home/lev/Work/miniconda/envs/NK1/lib/python2.7/site-packages/pandas/core/indexing.pyc in _get_setitem_indexer(self, key)
    107 
    108         try:
--> 109             return self._convert_to_indexer(key, is_setter=True)
    110         except TypeError:
    111             raise IndexingError(key)

/home/lev/Work/miniconda/envs/NK1/lib/python2.7/site-packages/pandas/core/indexing.pyc in _convert_to_indexer(self, obj, axis, is_setter)
   1110                 mask = check == -1
   1111                 if mask.any():
-> 1112                     raise KeyError('%s not in index' % objarr[mask])
   1113 
   1114                 return _values_from_object(indexer)

KeyError: "[('a', 'b')] not in index"