Add support for namespaces

[jgeewax]

These exist to an extent but aren't universal and certainly not well documented.

There are two options:

1. Create an object to manage namespaces

from gcloud import datastore
dataset = datastore.get_dataset(...)
namespace = dataset.namespace('my-namespace')
person = namespace.entity('Person')
person['name'] = 'JJ'
person.save()

query = namespace.query('Person')
print query.fetch()

2. Allow users to pass a namespace argument to various constructors (and set namespaces with a method, akin to setting a kind or id on a Key).

from gcloud import datastore
dataset = datastore.get_dataset(...)
person = dataset.entity('Person')
person.namespace('my-namespace')
person['name'] = 'JJ'
person.save()

query = dataset.query('Person').namespace('my-namespace')
print query.fetch()

or

person = namespace.entity('Person')
person['name'] = 'JJ'
person.save(namespace='my-namespace')

I currently prefer option 2, where a namespace isn't a separate level in the hierarchy, but simply a flag passed around on queries or entities.

[proppy]

I think in 2) examples you meant person = dataset.entity('Person') not person = namespace.entity('Person')

[jgeewax]

Updated.

[tseaver]

I believe we address all the cases in the protobuf spec:

• Keys carry a '_namespace' attribute.
• 'Connection.run_query' accepts a 'namespace' argument.
• PR Fix #170: handle namespaces in queries #255 adds namespace support to queries.

Please re-open if we've missed a case.