basic role based delegation of env object in python's Fabric - (untested but should work)

gistfile1.py

import os

import fabric
from fabric.api import *
from fabric.api import run, roles, execute
from fabric.operations import sudo

if env.ssh_config_path and os.path.isfile(os.path.expanduser(env.ssh_config_path)):
    env.use_ssh_config = True

"""
every key in  'localbox' dict (appearing in roledefs) is set as a key/val pair 
on the 'env' object when @roles('localbox') decorates a function - context manager

""" 

roledefs = {
    'localbox':{
        'hosts':['nona@127.0.0.1'],
        'keyfiles':{'nona@127.0.0.1':'~/.ssh/id_rsa.pub'},
        'os':'osx'
    },
    'ottowa':{
        'hosts':['otto@127.0.0.1'],
        'passwords':{
            'otto@127.0.0.1':uid
        },
        'os':'osx'
    },
    'shanghai':{
        'hosts':['ubuntu@jws'],
        'key_filename':'~/.ssh/_gis.pem',
        'os':'ubuntu'
    }
}

"""
where we register multiple environments onto env which are selected by @roles decorator
"""
env.roledefs = {
    'localbox':roledefs.get('localbox'),
    'ottowa':roledefs.get('ottowa'),
    'shanghai':roledefs.get('shanghai')
}

def update_ubuntu():
    run('sudo apt-get update')

def update_osx():
    run('sudo softwareupdate -i -a')

def update_by_os():
    if env.os == 'osx':
        update_osx()
    if env.os == 'ubuntu':
        update_ubuntu()

@roles('localbox', 'ottowa', 'shanghai')
def update_servers():
    execute(update_by_os)