[Numpy-discussion] Baffling TypeError using fromfunction with explicit cast

[Thomas Coffee]

Somewhat new to NumPy, but I've been investigating this for over an hour
and found nothing helpful:

Can anyone explain why this works ...


>>> import numpy
>>> numpy.fromfunction(lambda i, j: i*j, (3,4))
array([[ 0.,  0.,  0.,  0.],
       [ 0.,  1.,  2.,  3.],
       [ 0.,  2.,  4.,  6.]])


... but neither of these do?


>>> numpy.fromfunction(lambda i, j: float(i*j), (3,4))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/pymodules/python2.7/numpy/core/numeric.py", line 1617, in
fromfunction
    return function(*args,**kwargs)
  File "<stdin>", line 1, in <lambda>
TypeError: only length-1 arrays can be converted to Python scalars


>>> numpy.fromfunction(lambda i, j: numpy.float(i*j), (3,4))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/pymodules/python2.7/numpy/core/numeric.py", line 1617, in
fromfunction
    return function(*args,**kwargs)
  File "<stdin>", line 1, in <lambda>
TypeError: only length-1 arrays can be converted to Python scalars


Given that fromfunction casts the return values to float by default, why
does it break when this cast is made explicit?

The motivation for the question is to be able to use fromfunction with a
function that can return infinity, which I only know how to create with the
explicit cast float('inf').

Thanks in advance for your help!

- Thomas
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.python.org/pipermail/numpy-discussion/attachments/20111224/7cead7fa/attachment.html>