vectorize fails for zero-dimensioned arrays

The following used to work and return an empty 5 by 0 array.

np.vectorize(lambda x: x+1)(np.zeros([5,0]))

Now it stack traces:

/usr/lib/python2.7/dist-packages/numpy/lib/function_base.pyc in __call__(self, *args, **kwargs)
   1571             vargs.extend([kwargs[_n] for _n in names])
   1572 
-> 1573         return self._vectorize_call(func=func, args=vargs)
   1574 
   1575     def _get_ufunc_and_otypes(self, func, args):

/usr/lib/python2.7/dist-packages/numpy/lib/function_base.pyc in _vectorize_call(self, func, args)
   1631             _res = func()
   1632         else:
-> 1633             ufunc, otypes = self._get_ufunc_and_otypes(func=func, args=args)
   1634 
   1635             # Convert args to object arrays first

/usr/lib/python2.7/dist-packages/numpy/lib/function_base.pyc in _get_ufunc_and_otypes(self, func, args)
   1594             # Assumes that ufunc first evaluates the 0th elements in the input
   1595             # arrays (the input values are not checked to ensure this)
-> 1596             inputs = [asarray(_a).flat[0] for _a in args]
   1597             outputs = func(*inputs)
   1598 

IndexError: index 0 is out of bounds for axis 0 with size 0
> /usr/lib/python2.7/dist-packages/numpy/lib/function_base.py(1596)_get_ufunc_and_otypes()
   1595             # arrays (the input values are not checked to ensure this)
-> 1596             inputs = [asarray(_a).flat[0] for _a in args]
   1597             outputs = func(*inputs)

Seems to me that there should first be a check for empty arrays before attempting to see the return types of the function?

[seberg]

Sure, this would be better to work again if possible (even if I don’t like vectorize much 😉). The code seems only for output type detection (which may indeed be tricky with empty arguments).

So the workaround is:

np.vectorize(lambda x: x+1, otypes=[np.float64])(np.zeros([5,0]))

[shoyer]

I added handling for size 0 inputs (basically, just a better error message) in https://github.com/numpy/numpy/pull/8054