Collections could benefit from key'd lookup

[nikhilk]

Example:

datasets = bq.DataSets(project_id = 'cloud-datalab')
for ds in datasets:
  print ds.name

The result is a listing. Next step is to work against one of the items.

Try, datasets['sampledata']

--> error: TypeError: 'DataSets' object has no attribute 'getitem'

Try: datasets[3]

--> error: TypeError: 'DataSets' object does not support indexing

Ideally both positional and key'd indexing into collections should work.