Override Index.astype to prevent bad things from happening

[wesm]

For example, this should be possible: index.astype('i8')

[ralphbean]

What kind of bad things? I can't seem to see what the bug is.

For instance, with a freshly checked out copy of pandas I can do this::

>>> i = pandas.Index([1,2,3])
>>> i
Index([1, 2, 3], dtype=object)
>>> i.astype('i8')
Index([1, 2, 3])
>>> i.astype('str')
Index(['1', '2', '3'], 
      dtype='|S1')
>>> i =pandas.Index([1,2,'foo'])
>>> i
Index([1, 2, foo], dtype=object)
>>> i.astype('str')
Index(['1', '2', 'f'], 
      dtype='|S1')
>>> i.astype('i8')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: invalid literal for long() with base 10: 'foo'

[wesm]

internal Cython routines assume that dtype=object

In [1]: idx = Index([1,2,3])

In [2]: idx
Out[2]: Index([1, 2, 3], dtype=object)

In [3]: casted = idx.astype('i8')

In [4]: casted.get_loc(2)
ERROR: An unexpected error occurred while tokenizing input
The following traceback may be corrupted or invalid
The error message is: ('EOF in multi-line statement', (65, 0))
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
/Users/wesm/Dropbox/book/svn/<ipython-input-4-5218f9d38465> in <module>()
----> 1 casted.get_loc(2)

/Users/wesm/code/pandas/pandas/core/index.pyc in get_loc(self, key)
    433         loc : int
    434         """
--> 435         return self._engine.get_loc(key)
    436 
    437     def get_indexer(self, target, method=None):

/Users/wesm/code/pandas/pandas/_engines.so in pandas._engines.DictIndexEngine.get_loc (pandas/src/engines.c:1467)()

/Users/wesm/code/pandas/pandas/_engines.so in pandas._engines.DictIndexEngine.get_loc (pandas/src/engines.c:1419)()

/Users/wesm/code/pandas/pandas/_engines.so in pandas._engines.DictIndexEngine._ensure_initialized (pandas/src/engines.c:1144)()

/Users/wesm/code/pandas/pandas/_engines.so in pandas._engines.DictIndexEngine.initialize (pandas/src/engines.c:1310)()

/Users/wesm/code/pandas/pandas/_tseries.so in pandas._tseries.map_indices_object (pandas/src/tseries.c:25134)()

ValueError: Buffer dtype mismatch, expected 'Python object' but got 'long'