This seems to be a old problem but I've recently hit with this in a very random way (I'm using numpy 1.6.1).  There seems to be a ticket (1239) but it seems the issue is unscheduled.   Can somebody tell me if this is fixed? 
In particular, it makes for a very unstable behavior when you try to reference something from a string array and pickle it across the wire.  For example:

In [1]: import numpy
In [2]: a = numpy.array(['a', '', 'b'])
In [3]: import cPickle
In [4]: s = cPickle.dumps(a[1])
In [5]: cPickle.loads(s)
TypeError                                 Traceback (most recent call last)
/auto/cnvtvws/wlee/fstrat/src/<ipython-input-5-555fae2bd4f5> in <module>()
----> 1 cPickle.loads(s)
TypeError: ('data type not understood', <type 'numpy.dtype'>, ('S0', 0, 1))
Note that if you reference a[0] and a[2], it would work, so you're in the case where sometimes it'd work but sometimes it won't.  Checking for this case in the code and work around it would really be a pain. 
On Thu, Sep 24, 2009 at 7:03 PM, David Warde-Farley <> wrote:
On 23-Sep-09, at 7:55 PM, David Warde-Farley wrote:

> It seems that either dtype(str) should do something more sensible than
> zero-length string, or it should be possible to create it with
> dtype('|
> S0').  Which should it be?

Since there wasn't any response I went ahead and fixed it by making
str and unicode dtypes allow a size of 0 when constructed with
protocol type codes. Either S0 and U0 should be constructable with
typecodes or they shouldn't be allowed at all; I opted for the latter
since a) it was simple and b) I don't know what a sensible default for
dtype(str) would be (length 1? length 10?).

Patch is at:

Review away!

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