[Numpy-discussion] ufunc.accumulate question
Chris Withers
chris@simplistix.co...
Tue Oct 5 07:53:22 CDT 2010
Hi All,
I can't find any docs on this behavior.
So, I have a python function. To keep it simple, lets just do addition:
def add(x,y):
print x,y
retun x+y
So, I can turn this into a ufunc as follows:
uadd = np.frompyfunc(add,2,1)
Now, I can apply it to an array:
>>> uadd.accumulate(np.arange(3,10))
3 4
7 5
12 6
18 7
25 8
33 9
array([3, 7, 12, 18, 25, 33, 42], dtype=object)
Okay, but where did the initial 3 come from?
http://docs.scipy.org/doc/numpy/reference/generated/numpy.ufunc.accumulate.html#numpy.ufunc.accumulate
suggests that:
r = np.empty(len(A))
t = op.identity # op = the ufunc being applied to A's elements
for i in xrange(len(A)):
t = op(t, A[i])
r[i] = t
return r
...but:
>>> print uadd.identity
None
...and:
>>> add(None,3)
None 3
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "<stdin>", line 3, in add
TypeError: unsupported operand type(s) for +: 'NoneType' and 'int'
So, where is the reason that the 3 ends up in the output array documented?
Also, what if I want to specify the identity of my newly created ufunc?
I have a case where I want to specify it as zero:
>>> uadd.identity = 0
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
AttributeError: attribute 'identity' of 'numpy.ufunc' objects is not
writable
Any help gratefully received!
Chris
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