Nicolas Rougier wrote:
I would like to create numpy array with my own (python) datatype, so I tried the obvious solution:
from numpy import * class Unit(object): def __init__(self,value=0.0): self.value = value def __float__(self): return self.value def __repr__(self): return str(self.value)
a = array (array([[1,2],[3,4]]), dtype=Unit)
the dtype argument is designed to take a numpy type object, not an arbitrary class -- what you want in this case is dtype=numpy.object, which is what you did before. I'm a surprised this didn't raise an error, but it looks like you got an object array, but you objects you gave it are python integers. All python classes are "objects" as far an numpy is concerned. The numpy dtypes are a description of a given number of bytes in memory -- python classes are stored as a pointer to the python object. (and you really don't want to use "import *")
Also, the commented line (a[0,0] = 0) makes the item to become an int while I need to set the value of the item instead, is that possible ?
a[0,0] = Unit(0) You're setting the [0,0]th element to an object, you need to give it the object you want, the literal "0" is a python integer with the value zero. numpy arrays of python objects act a whole lot like other python containers. What would you expect from : a = [1,2,3,4] a list of integers, no? or a = [Unit(1), Unit(2)] # a list of Units.. then # a[0] = 3 now a list with the integer3 in the zeroth position, and a Unit in the 1st. You did it right the first time: a = array([[Unit(1), Unit(2)], [Unit(3), Unit(4)]]) though you need to be careful building object arrays of nested lists -- numpy won't unnecessarily figure out how do d-nest it. You might want to do:
import numpy as np a = np.empty((2,2), np.object) a array([[None, None], [None, None]], dtype=object) a[:,:] = [[Unit(1), Unit(2)], [Unit(3), Unit(4)]] a array([[1, 2], [3, 4]], dtype=object)
One more note: class Unit(object): def __init__(self,value=0.0): self.value = value def __float__(self): return self.value def __repr__(self): return str(self.value) __repr__ really should be something like: def __repr__(self): return "Unit(%g)%self.value" eval(repr(Object)) == Object, ideally, plus it'll be easier to debug if you can see what it is. -Chris -- Christopher Barker, Ph.D. Oceanographer Emergency Response Division NOAA/NOS/OR&R (206) 526-6959 voice 7600 Sand Point Way NE (206) 526-6329 fax Seattle, WA 98115 (206) 526-6317 main reception Chris.Barker@noaa.gov