[SciPy-Dev] issue pickling an interp1d object

[Johann Cohen-Tanugi]

Dear Scipy-ers,
I sent the email below to the user list yesterday, but perhaps this one 
is a better medium. I forgot to mention that the problem is likely 
related to the fact that I am using the interpolators within parallel 
snippet of codes, using the multiprocessing module. It seems that 
interp1d is not safe in the context of such usage, contrary (seemingly) 
to InterpolatedUnivariateSpline. I do not know whether this is a bug or 
a feature, and I have an obvious workaround, saving the arrays rather 
than the interpolator
  objects themselves.

best,
Johann

-------------------
Dear Scipy-ers,
I am using scipy (0.15.1) to interpolate a fairly complicate double 
integral for several parameters, for later use in yet a third integral. 
The pickling is thus of a dict of interpolators. When I am using 
InterpolatedUnivariateSpline my code runs smoothly and dump a pickled 
file. But when I use interp1d (with default protocol 0), I crash :
Traceback (most recent call last):
     pickle.dump( interpolators, f )
   File "/usr/lib/python2.7/pickle.py", line 1370, in dump
     Pickler(file, protocol).dump(obj)
   File "/usr/lib/python2.7/pickle.py", line 224, in dump
     self.save(obj)
   File "/usr/lib/python2.7/pickle.py", line 286, in save
     f(self, obj) # Call unbound method with explicit self
   File "/usr/lib/python2.7/pickle.py", line 649, in save_dict
     self._batch_setitems(obj.iteritems())
   File "/usr/lib/python2.7/pickle.py", line 663, in _batch_setitems
     save(v)
   File "/usr/lib/python2.7/pickle.py", line 306, in save
     rv = reduce(self.proto)
   File "/usr/lib/python2.7/copy_reg.py", line 77, in _reduce_ex
     raise TypeError("a class that defines __slots__ without "
TypeError: a class that defines __slots__ without defining __getstate__ 
cannot be pickled

When I set the protocol to -1, I get a different crash :
     pickle.dump( interpolators, f, protocol=-1 )
   File "/usr/lib/python2.7/pickle.py", line 1370, in dump
     Pickler(file, protocol).dump(obj)
   File "/usr/lib/python2.7/pickle.py", line 224, in dump
     self.save(obj)
   File "/usr/lib/python2.7/pickle.py", line 286, in save
     f(self, obj) # Call unbound method with explicit self
   File "/usr/lib/python2.7/pickle.py", line 649, in save_dict
     self._batch_setitems(obj.iteritems())
   File "/usr/lib/python2.7/pickle.py", line 681, in _batch_setitems
     save(v)
   File "/usr/lib/python2.7/pickle.py", line 331, in save
     self.save_reduce(obj=obj, *rv)
   File "/usr/lib/python2.7/pickle.py", line 419, in save_reduce
     save(state)
   File "/usr/lib/python2.7/pickle.py", line 286, in save
     f(self, obj) # Call unbound method with explicit self
   File "/usr/lib/python2.7/pickle.py", line 548, in save_tuple
     save(element)
   File "/usr/lib/python2.7/pickle.py", line 286, in save
     f(self, obj) # Call unbound method with explicit self
   File "/usr/lib/python2.7/pickle.py", line 649, in save_dict
     self._batch_setitems(obj.iteritems())
   File "/usr/lib/python2.7/pickle.py", line 681, in _batch_setitems
     save(v)
   File "/usr/lib/python2.7/pickle.py", line 331, in save
     self.save_reduce(obj=obj, *rv)
   File "/usr/lib/python2.7/pickle.py", line 396, in save_reduce
     save(cls)
   File "/usr/lib/python2.7/pickle.py", line 286, in save
     f(self, obj) # Call unbound method with explicit self
   File "/usr/lib/python2.7/pickle.py", line 748, in save_global
     (obj, module, name))
pickle.PicklingError: Can't pickle <type 'instancemethod'>: it's not 
found as __builtin__.instancemethod

Does that ring a bell to anyone, before I start simplifying my code to 
provide this list with a test case?
Thanks a lot in advance,
Johann