Take this case:

class a(A):
    class Hosts:
        app = [host0, host1]
        lb = [host2, host3]

    @map_roles(host=('app', 'lb'))
    class git(Git):
         pass

Now I can do the following to git show the load balancers:

> a git :host2 show
> a git :host3 show

However, instead of doing this individually, I would like to use the already defined lb role mapping. Something like:

 > a %lb git show

So when resolving the hosts to pass to Git, we will filter out the hosts that are not part of the lb role of the parent service. The difference is that filtering by host isolation happens after you select the service, while filtering by host mapping happens before - I think that makes sense, as the mappings come from the parent service.

@don’t_isolate_yet

It should only be applied to a method of a ParallelNode. The API should make sure that
the `self`` object looks like an unisolated node array.

Right now this is not the case when such a method is called from another method of the same node. (which is isolated) In this case, we should covert self to an array of just one Host, in order to be API compatible.

We should be able to do this:

with host.open('/file') as f:
   for line in f:
     ....

Right now, people have to do something like this:

with host.open('/file') as f:
   for line in f.read().splitlines():
     ....

When multiple threads act on the same host, (That is exceptional, it doesn't happen in our own deployment, but it can happen.), and threads change the context by executing a with cd-command, this context is changed in the other threads as well.

The solution is probably to clone the hosts contexts as soon as a new thread i created, or to make it immutable, and copy it around in the Env object.

Would be nice either this library supported python3, or at least the docs+readme mentioned that.

$ python --version
Python 3.5.2

$ python
>>> from deployer.host import SSHHost
ImportError: No module named 'StringIO'