[yt-dev] Issue #825: Creating an all_data object does not generate the field_info object. (yt_analysis/yt)

[Sam Skillman]

I personally find the behavior of field_info to be one of the biggest
friction points in my day-to-day use and development in yt.  Specifically,
I really think that if I ask to access field_info, it should be filled
out/constructed automatically.  At the very least I think we should move
_get_field_info to get_field_info, and then people might think to use that
rather than access the field_info container directly.  In fact, if that's
the route we go, we should even consider moving field_info to _field_info
since it is a less stable interface to the information.

My $0.02


On Tue, Apr 1, 2014 at 5:14 PM, Nathan Goldbaum <nathan12343 at gmail.com>wrote:

> I've opened a PR here that fixes it:
> https://bitbucket.org/yt_analysis/yt/pull-request/784/generate-the-index-for-the-total_mass/diff
>
> I think this is a special case - it's the only derived quantity that uses
> the `field_info` like this.
>
>
> On Tue, Apr 1, 2014 at 5:08 PM, Matthew Turk <matthewturk at gmail.com>wrote:
>
>> I think so, yes.  That manually instantiates the index.
>>
>> Now, I guess the bigger question is, *should* this be the fix, or
>> should we somehow transparently catch this, and pass all the
>> _get_field_info logic into __getitem__ in the field info container?  I
>> am torn on that front.
>>
>> On Tue, Apr 1, 2014 at 8:06 PM, Nathan Goldbaum <nathan12343 at gmail.com>
>> wrote:
>> > Hi Matt,
>> >
>> > So the fix would be to get the field_info via _get_field_info in
>> __call__
>> > for the derived quantity?
>> >
>> > -Natan
>> >
>> >
>> > On Tue, Apr 1, 2014 at 5:04 PM, Matthew Turk <matthewturk at gmail.com>
>> wrote:
>> >>
>> >> Hi Nathan,
>> >>
>> >> This was by design -- whether that was right or not -- because I
>> >> wanted to allow all of the objects to be created without requiring an
>> >> index, until data was accessed.  Specifically this fails because
>> >> TotalMass accesses field_info directly instead of via _get_field_info.
>> >>
>> >> -Matt
>> >>
>> >> On Tue, Apr 1, 2014 at 8:02 PM, Nathan Goldbaum
>> >> <issues-reply at bitbucket.org> wrote:
>> >> > New issue 825: Creating an all_data object does not generate the
>> >> > field_info object.
>> >> >
>> >> >
>> https://bitbucket.org/yt_analysis/yt/issue/825/creating-an-all_data-object-does-not
>> >> >
>> >> > Nathan Goldbaum:
>> >> >
>> >> > The following script and traceback illustrates the issue:
>> >> >
>> >> >
>> >> > ```
>> >> > #!python
>> >> >
>> >> > import yt
>> >> >
>> >> > ds = yt.load('IsolatedGalaxy/galaxy0030/galaxy0030')
>> >> >
>> >> > ad = ds.all_data()
>> >> >
>> >> > print ad.quantities.total_mass()
>> >> > ```
>> >> >
>> >> >
>> >> > ```
>> >> >   File "test.py", line 7, in <module>
>> >> >     print ad.quantities.total_mass()
>> >> >   File
>> >> >
>> "/Users/goldbaum/Documents/yt-hg/yt/data_objects/derived_quantities.py",
>> >> > line 188, in __call__
>> >> >     fi = self.data_source.pf.field_info
>> >> > AttributeError: 'EnzoDataset' object has no attribute 'field_info'
>> >> >
>> >> > ```
>> >> >
>> >> > Adding a call to ds.index before the call to the `total_mass` derived
>> >> > quantity eliminates the error.
>> >> >
>> >> >
>> >> >
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