Use Python data structures to define datashape

[mrocklin]

We currently use lots of internal data structures like Tuple, Record and DataShape to construct datashapes. Maybe we can get away with tuple, ordereddict, and list?

`10 * var * {name: string}`

DataShape([10, var, OrderedDict([['name', 'string']]))

This might make traversing these data structures much cleaner. I think that this choice should be mostly invisible to the user.

[FRidh]

I can imagine such a change would make it also easier for users to generate a datashape, since you don't have to make a string out of a mapping.

For example, I am currently using a parallel map for computations, outputting tuples. The tuples just contain data, no meta-information. I would like to write this data into a file using into, and this requires a dshape. The first couple of columns contain strings, the other datetimes. I would prefer to only having to generate a mapping with column names and types in the form of an OrderedDict and perhaps add var, than to also having to build a dshape string out of it afterwards.

[mrocklin]

I very much agree. As a temporary fix you can create a datashape from data structures if you are willing to use some of the internal API.

In [1]: import datashape as ds

In [2]: ds.var * ds.Record([['name', ds.string], ['balance', ds.int64 ]])
Out[2]: dshape("var * {name: string, balance: int64}")