ENH: Add HashableIndexes to core/index.py

Author: jtratner

pandas/core/common.py

@@ -9,6 +9,7 @@
 
 import itertools
 from datetime import datetime
+import types
 
 from numpy.lib.format import read_array, write_array
 import numpy as np
@@ -42,6 +43,30 @@ class AmbiguousIndexError(PandasError, KeyError):
     pass
 
 
+def bind_method(cls, name, func):
+    """Bind a method to class, python 2 and python 3 compatible.
+
+    Parameters
+    ----------
+
+    cls : type
+        class to receive bound method
+    name : basestring
+        name of method on class instance
+    func : function
+        function to be bound as method
+
+
+    Returns
+    -------
+    None
+    """
+    # only python 2 has bound/unbound method issue
+    if not py3compat.PY3:
+        setattr(cls, name, types.MethodType(func, None, cls))
+    else:
+        setattr(cls, name, func)
+
 _POSSIBLY_CAST_DTYPES = set([ np.dtype(t) for t in ['M8[ns]','m8[ns]','O','int8','uint8','int16','uint16','int32','uint32','int64','uint64'] ])
 _NS_DTYPE = np.dtype('M8[ns]')
 _TD_DTYPE = np.dtype('m8[ns]')

pandas/core/index.py

@@ -11,7 +11,7 @@
 from pandas.lib import Timestamp
 
 from pandas.util.decorators import cache_readonly
-from pandas.core.common import isnull
+from pandas.core.common import isnull, bind_method
 import pandas.core.common as com
 from pandas.util import py3compat
 from pandas.core.config import get_option
@@ -2688,6 +2688,53 @@ def _wrap_joined_index(self, joined, other):
         return MultiIndex.from_tuples(joined, names=names)
 
 
+def hashable_class_factory(klass, hash_func=None):
+    """Creates Hashable Class for given Index type
+    and adds `ashashable` method to the Index"""
+
+    class HashableIndexMixin(object):
+        """
+        Implements hashing methods...note that this is
+        very crude, and *only* works if it's mixed into a parent
+        class that is a subclass of (or just is) an index
+        """
+
+        def __init__(self, index):
+            self._index = index
+
+        def __eq__(self, other):
+            if issubclass(other, klass):
+                return (self.values == other.values).all()
+            else:
+                return False
+
+        if hash_func:
+            __hash__ = hash_func
+        else:
+            def __hash__(self):
+                return hash(str(self))
+
+        # should this be a property??
+        def asindex(self):
+            return self._index
+
+    HashableClass = type("Hashable{klass}".format(klass=klass.__name__), (HashableIndexMixin, klass))
+
+    def ashashable(self):
+        """convert {klass} to a hashable type that
+         can be used for key/value lookup
+        """
+        return HashableClass(self)
+
+    ashashable.__doc__ = ashashable.__doc__.format(klass=klass.__name__)
+    bind_method(klass, "ashashable", ashashable)
+
+    return HashableClass
+
+HashableIndex = hashable_class_factory(Index)
+HashableInt64Index = hashable_class_factory(Int64Index)
+HashableMultiIndex = hashable_class_factory(MultiIndex)
+
 # For utility purposes
 
 def _sparsify(label_list, start=0,sentinal=''):