On Do, 2015-04-09 at 21:30 -0700, Elliot wrote:

Hi all,

Sorry if this is the wrong forum for a question like this.

I'm trying to create an object with multiple inheritance, one of which is from numpy.ndarray. The other gives it cacheable properties and defines a __getattr__ to deliver the cached properties. The initial instantiation is successful, but ufuncs and slices cause an infinite recursion where the __getattr__ function is used but the _cacheable attribute is not set (ie: from __init__ )

You have a typo in your __array_finalize__ it misses the last underscore, that is probably why it is never called. About the infinite recursion, not sure on first sight.

I am using docs.scipy.org/doc/numpy/user/basics.subclassing.html as a reference. Here is code that shows my problem (python 2.7, numpy 1.8.2)

=====================

from __future__ import print_function import numpy as np

class Cacheable(object):

def __init__(self,*args,**kwargs):
    self._cacheable = {}

def __getattr__(self,key):
   print("getting %s"%key)
   if key in self._cacheable:
     print("  found it")
     self._cacheable[key]()
     return self.__dict__[key] #if chache function does't update
     # data you're going to have a bad time
   else:
     raise AttributeError

def _clear(self):
    '''clears derived properties'''
    for key in self._cacheable:
      if key in self.__dict__:
        del self.__dict__[key]

class BaseGeometry(np.ndarray,Cacheable): '''Numpy array with extra attributes that are cacheable arrays'''

def __new__(cls,input_array,dtype=np.float64,*args,**kwargs):
    # Input array is an already formed ndarray instance
    # We first cast to be our class type
    obj = np.asarray(input_array,dtype=dtype).view(cls)
    # Finally, we must return the newly created object:
    return obj

def __init__(self,dims=None,dtype=np.float64,readonly=True):
    #TODO: sort through args and kwargs to make better 
    self.readonly=readonly
    if readonly:
       self.flags.writeable=False
    self.dims=dims
    self._dtype = dtype
    Cacheable.__init__(self)

def writeable_copy(self):
    ret = np.copy(self)
    ret.flags.writeable = True
    return ret

def __array_finalize_(self,obj):
   #New object, will be created in __new__
   print("array_finalize")
   if obj is None: return
   # created from slice or template
   print("finalizing slice")
   self._cacheable = getattr(obj, '_cacheable', None)

if __name__ == "__main__": n = 5 test = BaseGeometry(np.random.randint(-25,25,(n,2))) print("this works:",test._cacheable) broken = test[1:4] #interestingly, no problem here print(broken) #infinite recursion

===================

array_finalize is never called.

output is:

this works: {} getting _cacheable getting _cacheable getting _cacheable

[and on and on]

getting _cacheable getting _cacheable <repr(&lt;__main__.BaseGeometry at 0x7fa42e2921b8>) failed: RuntimeError: maximum recursion depth exceeded while calling a Python object>

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