Add keep_attrs to reduction methods

[jhamman]

fixes #138

This is a much cleaner version of #139.

[shoyer]

I would just use assertEqual here, which works perfectly fine for dictionaries (you don't need utils.dict_equal unless you have numpy arrays instead your dicts).

[jhamman]

Good to know. Thanks.

[shoyer]

Probably better to move it a closer to where attrs is used (at the end of the function).

If you like, you could make it a one-liner:

attrs = self.attrs if keep_attrs else {}

(The attributes dictionary is always copied, so it doesn't matter whether you provide it as an OrderedDict or a normal dict.)

[jhamman]

I like it. Done.

[shoyer]

This is another style issue (and you can see the existing test code isn't great at this), but in general I would rather not make global variables. It's more self-contained and obvious. In this case, you could simply move _attrs to inside test_reduce_keep_attrs.

[jhamman]

Yeah, no problem. I'm generally a fan of keeping fixtures as local as possible. In this case, I think I was matching the existing code style.

[shoyer]

Could you update the signature and documentation of methods like mean, sum, etc?

[shoyer]

The to update the signature of the reduce methods, you would need to update the function inside the _reduce_method class method.

[jhamman]

Ok, is this what you mean? Sorry - wasn't tracking with you there.

[shoyer]

Yes, thanks!