sorry, I see your reply today.
in sagecloud:
sage: K.<z> = QuadraticField(-23);K
Number Field in z with defining polynomial x^2 + 23
sage: p = K.primes_above(3)[0];p
Fractional ideal (3, 1/2*z - 1/2)
sage: p.ray_class_number()
---------------------------------------------------------------------------
AttributeError Traceback (most recent call last)
<ipython-input-12-8ba0cf693043> in <module>()
----> 1 p.ray_class_number()
/usr/local/sage/sage-5.12/local/lib/python2.7/site-packages/sage/structure/element.so in sage.structure.element.Element.__getattr__ (sage/structure/element.c:3871)()
/usr/local/sage/sage-5.12/local/lib/python2.7/site-packages/sage/structure/misc.so in sage.structure.misc.getattr_from_other_class (sage/structure/misc.c:1696)()
AttributeError: 'NumberFieldFractionalIdeal' object has no attribute 'ray_class_number'
in http://sagenb.skku.edu/
K.<z> = QuadraticField(-23);
p = K.primes_above(3)[0];
p.ray_class_number()
Traceback (click to the left of this block for traceback)
...
AttributeError: 'NumberFieldFractionalIdeal' object has no attribute 'ray_class_number'
It works for me, i got: sage: I.ray_class_number() 5184 Could you please send us the error message ?