Basic state machine implementation in Python using namedtuples as states and functions as transitions

state_machine.py

from collections import namedtuple
import re
import sys


SIGNALFX_API = 'https://app.signalfx.com/#/'
RES_TYPE_RE= re.compile(r"^(?P<type>\S+?)\..*:$")


# STATES
NoResource = namedtuple('NoResource', 'output')
EmptyResource = namedtuple('EmptyResource', '')
NewResource = namedtuple('NewResource', ('type',))
NamedResource = namedtuple('NamedResource', ('type', 'name'))
IdResource = namedtuple('IdResouce', ('type', 'id'))
CompleteResource = namedtuple('CompleteResource', ('type', 'name', 'id'))
End = namedtuple('End', '')


# ACTIONS
def show_no_state(state):
    print(state.output)


def show(state):
    print(state.type)
    print(state.name)
    print(SIGNALFX_API + state.type + '/' + state.id + '/edit\n')


# TRANSITIONS
def itself(state, input):
    return state


def end(state, input):
    return End()


def empty(state, input):
    return EmptyResource()


def no_state(state, input):
    if 'No state' in input:
        return NoResource(input)


def new_resource(state, input):
    match = RES_TYPE_RE.match(input)
    if match:
        return NewResource(match.group('type'))


def name_resource(state, input):
    input = input.strip()
    if input.startswith('name ='):
        name = input.split('name = ', 1)[1].strip()
        if isinstance(state, NewResource):
            return NamedResource(state.type, name)
        else:
            return CompleteResource(state.type, name, state.id)


def id_resource(state, input):
    input = input.strip()
    if input.startswith('id ='):
        res_id = input.split('id =', 1)[1].strip()
        if isinstance(state, NewResource):
            return IdResource(state.type, res_id)
        else:
            return CompleteResource(state.type, state.name, res_id)


# STATE MACHINE
TRANSITIONS = {
    EmptyResource: (no_state, new_resource, itself),
    NewResource: (name_resource, id_resource, itself),
    NamedResource: (id_resource, itself),
    IdResource: (name_resource, itself),
    CompleteResource: (new_resource, empty),
    NoResource: (end,),
    End: (itself,),
}


ACTIONS = {
    NoResource: show_no_state,
    CompleteResource: show,
}


def parse(state, line):
    for tr in TRANSITIONS[type(state)]:
        new_state = tr(state, line)
        if new_state is not None:
            if type(new_state) in ACTIONS:
                ACTIONS[type(new_state)](new_state)
            return new_state
    raise ValueError("Unexpected state line: {0}\nState: {1}".format(line, state))


def parse_resource_state(resource_state):
    reduce(parse, resource_state, EmptyResource())


if __name__ == "__main__":
    parse_resource_state(sys.stdin)