If you try to set a longdouble scalar with a string, it appears to go through Python's normal string-parsing and therefore gets converted to a C double rather than a long double:

In [19]: numpy.longdouble("1.12345678901234567890")
Out[19]: 1.1234567890123456912

Note the loss of those last couple digits.

In [20]: numpy.float("1.12345678901234567890")
Out[20]: 1.1234567890123457

In [21]: numpy.longdouble("1.12345678901234567890") - numpy.float("1.12345678901234567890")
Out[21]: 0.0

And so internally they are identical.

One solution to this is a special case for longdoubles and to use strtold() to do the conversion.

Cheers,

Scott