[Numpy-discussion] Unexpected output using numpy.ndarray and __radd__
Mark Hoffmann
Mark.Hoffmann at dk.manbw.com
Fri Dec 15 09:42:24 CST 2006
Hi,
The following issue has puzzled me for a while. I want to add a
numpy.ndarray and an instance of my own class. I define this operation
by implementing the methods __add__ and __radd__. My programme
(including output) looks like:
#!/usr/local/bin/python
import numpy
class Cyclehist:
def __init__(self,vals):
self.valuearray = numpy.array(vals)
def __str__(self):
return 'Cyclehist object: valuearray = '+str(self.valuearray)
def __add__(self,other):
print "__add__ : ",self,other
return self.valuearray + other
def __radd__(self,other):
print "__radd__ : ",self,other
return other + self.valuearray
c = Cyclehist([1.0,-21.2,3.2])
a = numpy.array([-1.0,2.2,-2.2])
print c + a
print a + c
# ---------- OUTPUT ----------
#
# addprob $ addprob.py
# __add__ : Cyclehist object: valuearray = [ 1. -21.2 3.2] [-1.
2.2 -2.2]
# [ 0. -19. 1.]
# __radd__ : Cyclehist object: valuearray = [ 1. -21.2 3.2] -1.0
# __radd__ : Cyclehist object: valuearray = [ 1. -21.2 3.2] 2.2
# __radd__ : Cyclehist object: valuearray = [ 1. -21.2 3.2] -2.2
# [[ 0. -22.2 2.2] [ 3.2 -19. 5.4] [ -1.2 -23.4 1. ]]
# addprob $
#
# ----------------------------
I expected the output of "c+a" and "a+c" to be identical, however, the
output of "a+c" gets nested in an elementwise fashion. Can anybody
explain this? Is it a bug or a feature? I'm using Python 2.4.4c1 and
numpy 1.0. I tried the programme using an older version of Python and
numpy and there the result of "c+a" and "a+c" are identical.
Regards,
Mark Hoffmann
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