Initialize list of lists

[davidr...@gmail.com]

Hi guys,

I'm trying initialize a list of a lists in python but when I try initialize the sublist, pycapn emits this error:

AttributeError: 'capnp.lib.capnp._DynamicListBuilder' object has no attribute 'init'

My code (problematic line in blue):

myListProto = proto.init("myList", len(self._myList))
for i in xrange(len(self._myList)):
  subListProto = myListProto.init(i, len(self._myList[i]))
  for j in xrange(len(self._myList[i])):
    subListProto[i][j] = self._myList[i][j]


My proto class:

struct MyClassProto
{
  myList @0 :List(List(UInt32));
}

In sumary, how I initialize a sublist of variable length?

Thanks in advance,

David

[Jason Paryani]

Sorry, this was an oversight that is now fixed (https://github.com/jparyani/pycapnp/commit/a5bf532d53db37414d5e6b25f139ef237a854cc1). Thanks for reporting it!

However, you may not even need to use `init` in your case. A much simpler way to write this code is to set the field directly with the list, like so:

proto.myList = [[1], [2,3], [4,5,6]]

As long as the `self._myList` type in your examples is a Python built-in list() object, then you could do the following:

proto.myList = self._myList

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[Kamal Marhubi]

Jason—would you accept a patch to make that assignment work with any instance of `collections.Sequence`? It would increase pythonicity to not require it be a `__builtin__.list`.

[Jason Paryani]

I'd be open to it, but add them to the bottom of the if/else type checking chain since isinstance takes close to 100x as long as the current type checking. Take a look at https://github.com/jparyani/pycapnp/blob/a5bf532d53db37414d5e6b25f139ef237a854cc1/capnp/lib/capnp.pyx#L686 to see the logic for this. While you're at it, we should add the same for dict->collections.Mapping.

[Kamal Marhubi]

Sounds good. I'd found that part of the code from your patch. :-)

So are you suggesting that the special case for `list` and `dict` be left in place for performance reasons? Makes sense to me; just checking.

[Jason Paryani]

Yep, leave them in as fast paths.

[David Ragazzi]

Thanks for the quick response.

This direct approach didn't worked for me at first time:

proto.myList = [[1], [2,3], [4,5,6]]

But the problem is that I was converting a deque to list only using list(), now I'm converting manually and then settinh the proto with the generated list.

Thanks!

--

David Ragazzi
MSc in Sofware Engineer (University of Liverpool)
OS Community Commiter at Numenta.org
--
"I think James Connolly, the Irish revolutionary, is right when he says that the only prophets are those who make their future. So we're not anticipating, we're working for it."