Implementing HappyBase Table atomic counter helpers.

[dhermes]

No description provided.

[dhermes]

@jgeewax HappyBase also has a counter_set but as of now, I have made it NotImplemented because Bigtable doesn't have a way to make it atomic. WDYT is the right move here? I did make a note in the docstring of counter_get that

.. note::
Application code should **never** store a counter value directly;
use the atomic :meth:`counter_inc` and :meth:`counter_dec` methods
for that.

[tseaver]

@dhermes, @jgeewax: I'm pretty much offline until Thursday, 2016-02-25 (in Palo Alto teaching a course). Likewise for #1515, #1516, #1502, #1512, and #1513.

[theacodes]

This LGTM, although from a readability nit standpoint counter_inc is a little hard to follow at first glance. I'm unsure why.

[dhermes]

RE: "Hard to follow." That's the kind of feedback I was hoping to surface (by breaking into small PRs). Do you think the low-level row should handle more of the responsibilities? Do you think the method should use a helper? etc.

[theacodes]

Perhaps just some comments in-line. Poor example, but what is bytes_value = column_cells[0][0] doing exactly? Why [0][0]?

[theacodes]

(this also just may be my unfamiliarity with bigtable showing)

[dhermes]

I don't think it's your unfamiliarity, but that also is good in that you don't have a bias towards how things should be. I had to look up what [0][0] is for: Row.commit_modifications returns a dictionary keyed by column families. Each column family contains a dictionary keys by column names (within the family). Each column has a list of tuples. Each tuple is a pair of the bytes in the cell and the associated timestamp. It's enough to need a breather after the explanation.

[theacodes]

Wow, that is a lot to explain.

[dhermes]

Luckily the docstring proves that a picture is worth a thousand words:

{
u'col-fam-id': {
b'col-name1': [
(b'cell-val', datetime.datetime(...)),
(b'cell-val-newer', datetime.datetime(...)),
],
b'col-name2': [
(b'altcol-cell-val', datetime.datetime(...)),
],
},
u'col-fam-id2': {
b'col-name3-but-other-fam': [
(b'foo', datetime.datetime(...)),
],
},
}

[theacodes]

Ah, very helpful. Can you include a comment that notes the expected format of the column_cells object?

[dhermes]

@jonparrott PTAL

[theacodes]

LGTM, please squash commits.