There must be a more idiomatic way

sample.py

        for container in containers:
            p1 = re.compile('.*?kinto_read-only_(\d)$')
            p2 = re.compile('.*?kinto_master_(\d)$')
            print container['Names']
            if container['Names']:
                for name in container['Names']:
                    if p1.match(name):
                        ports = container['Ports']
                        for port in ports:
                            self.read_only['ip'] = port['IP']
                            self.read_only['port'] = port['PrivatePort']
                    if p2.match(name):
                        ports = container['Ports']
                        for port in ports:
                            self.master['ip'] = port['IP']
                            self.master['port'] = port['PrivatePort']

container_names = [c['Names'] for c in containers if c['Names']]

# global variables so we compile just once (o/wise it's not useful to compile)
_RE_READ_ONLY= re.compile('.*?kinto_read-only_(\d)$')
_RE_MASTER = re.compile('.*?kinto_master_(\d)$')

for container in containers:
    for name in container.get('Names', []):
        if _RE_READ_ONLY.match(name):
            _dict = self.read_only
        elif _RE_MASTER.match(name):
            _dict = self.master
        else:
            continue

        for port in container.get('Ports', []):
             # what happens if we have several ports here ? we'd overwrite the previous values
             # something looks wrong (list vs dict)
            _dict['ip'] = port['IP']
            _dict['port'] = port['PrivatePort']

something like this... ?

p1 = re.compile('.*?kinto_read-only_(\d)$')
p2 = re.compile('.*?kinto_master_(\d)$')

container_names = [c['Names'] for c in containers if c['Names']]
ports_by_name = {c['Names']: c['Ports'][-1] for c in containers if c['Names']}

for container_name in container_names:
    if p1.match(container_name):
        self.read_only['ip'] = ports_by_name[container_name]['IP'][-1]
        self.read_only['port'] = ports_by_name[container_name]['PrivatePort'][-1]
    elif p2.match(container_name):
        self.master['ip'] = ports_by_name[container_name]['IP'][-1]
        self.master['port'] = ports_by_name[container_name]['PrivatePort'][-1]

_RE_READ_ONLY = re.compile('.*?kinto_read-only_(\d)$')
_RE_MASTER = re.compile('.*?kinto_master_(\d)$')

def get_ports(self, containers):
    # use a list comprehension to filter out containers with names
    containers = [container for container in containers if 'Names' in container]
    for container in containers:
        if has_match(_RE_READ_ONLY, container['Names']):
            # seems like you are overriding, do you only want the last one?
            for port in container.get('Ports', {}):
                self.read_only['ip'] = port['IP']
                self.read_only['port'] = port['PrivatePort']

        if has_match(_RE_MASTER, container['Names']):
            for port in container.get('Ports', {}):
                self.master['ip'] = port['IP']
                self.master['port'] = port['PrivatePort']


def has_match(r, names):
    # check using a list comprehension
    return true in [true for name in names if r.match(name)]

nitpick: I would not use list comprehensions to filter out things, because it means you are looping over the whole list at most twice -- which is suboptimal