Cython Class, create NumPy with Zeros

Question

i am trying to create a cython class which creates a NumPy with zeros. Later i want to write float values in that Numpy... My python class looks like this:

class test:
    def __init__(self, b):
       self.b = b
       self.eTest = np.zeros((100, 100))

My cython class looks like this so far:

import numpy as np
cimport numpy as np
FTYPE = np.float
ctypedef np.float_t FTYPE_t
cdef class test:
   def __init__(self, b):
      cdef np.ndarray[FTYPE_t, ndim=2, mode='c'] eTest   <<<works fine without this line
      self.eTest = np.zeros((100,100), dtype=FTYPE)

My cython code doesn't work so far. I am struggling with the question how to create a NumPy of zeros (100, 100) without any Python. Is that even possible? I am not really familiar in cython, i am sorry if i am asking some really trivial questions!

Many thanks for all your help and advices!

i get a CompileError, so i guess something is wrong with the way i write the class?! — RandomDude
– RandomDude, Commented May 4, 2015 at 12:43
It is generally quite useful if you tell us what compiler error you get. — cfh
– cfh, Commented May 4, 2015 at 12:44

Cristián Antuña · Accepted Answer · 2015-05-04 14:02:40Z

2

Redefine your class::

  cdef class test:
  cdef double[:,:] eTest
  def __init__(self, b):
      cdef np.ndarray[FTYPE_t, ndim=2, mode='c'] tmp
      tmp = np.zeros((100,100), dtype=FTYPE)
      self.eTest = tmp

Your ndarray (tmp in this case) can only be local to a function (the constructor in this case), so you should declare first eTest as a buffer-supporting type (a memoryview in my example) and then copy the ndarray to it.

As a side comment, I would directly assign the zeros ndarray to eTest:

cdef class test:
      cdef double[:,:] eTest
      def __init__(self, b):
          self.eTest =  np.zeros((100,100), dtype=FTYPE)

But I kept your structure in case you needed it.

edited May 4, 2015 at 14:02

answered May 4, 2015 at 13:42

Cristián Antuña

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