[Numpy-discussion] dtype for a single char

sam tygier samtygier at yahoo.co.uk
Thu Mar 4 14:07:42 EST 2010

Robert Kern wrote:
> On Thu, Mar 4, 2010 at 02:34, sam tygier <samtygier at yahoo.co.uk> wrote:
>> Robert Kern wrote:
>>> On Wed, Mar 3, 2010 at 15:14, sam tygier <samtygier at yahoo.co.uk> wrote:
>>>> Hello
>>>> today i was caught out by trying to use 'a' as a dtype for a single character. a simple example would be:
>>>>>>> array([('a',1),('b',2),('c',3)], dtype=[("letter", "a"), ("number", "i")])
>>>> array([('', 1), ('', 2), ('', 3)],
>>>>      dtype=[('letter', '|S0'), ('number', '<i4')])
>>>> the fix seems to be using 'a1' instead
>>>>>>> array([('a',1),('b',2),('c',3)], dtype=[("letter", "a1"), ("number", "i")])
>>>> array([('a', 1), ('b', 2), ('c', 3)],
>>>>      dtype=[('letter', '|S1'), ('number', '<i4')])
>>>> this seems odd to me, as other types eg 'i' and 'f' can be used on their own. is there a reason for this?
>>> Other types have a sensible default determined by the platform.
>> I don't understand. char has sensible default size on my platform (and all the others i am familiar with), 1 byte.
> 'S' is not char.


somehow i had the impression that 'a' was a char. maybe to much back and forward between the dtype, and the python struct docs.



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