alexafsm
- Finite-state machine library for building complex Alexa conversations.
- Free software: Apache Software License 2.0.
Dialog agents need to keep track of the various pieces of information to make decisions how to respond to a given user input. This is referred to as context, session, or state tracking. As the dialog complexity increases, this state-tracking logic becomes harder to write, debug, and maintain. This library takes the finite-state machine design approach to address this complexity. Developers using this library can model dialog agents with first-class concepts such as states, attributes, transition, and actions. Visualization and other tools are also provided to help understand and debug complex FSM conversations.
Also check out our blog post.
Features
- FSM-based library for building Alexa skills with complex dialog state tracking.
- Tools to validate, visualize, and print the FSM graph.
- Support analytics with VoiceLabs.
- Can be paired with any Python server library (Flask, CherryPy, etc.)
- Written in Python 3.6 (primarily for type annotation and string interpolation).
Getting Started
Install from PyPi:
pip install alexafsm
Consult the Alexa skill search skill in the tests
directory for details of how to
write an alexafsm
skill. An Alexa skill is composed of the following three classes:
SessionAttributes
, States
, and Policy
.
SessionAttributes
SessionAttributes
is a class that holds session attributes (alexa_request['session']['attributes']
)
and any information we need to keep track of dialog state.
- The core attributes are
intent
,slots
, andstate
. intent
andslots
map directly to Alexa's concepts.slots
should be of typeSlots
, which in turn is defined as a named tuple, one field for each slot type. In the skill search example,Slots = namedtuple('Slots', ['query', 'nth']
). This named tuple class should be specified in the class definition asslots_cls = Slots
.state
holds the name of the current state in the state machine.- Each Alexa skill can contain arbitrary number of additional attributes. If an attribute is
not meant to be sent back to Alexa server (e.g. so as to reduce the payload size), it should
be added to
not_sent_fields
. In the skill search example,searched
andfirst_time
are not sent to Alexa server.
See the implementation of skill search skill's SessionAttributes
States
States
is a class that specifies most of the FSM and its behavior. It holds a reference to
a SessionAttributes
object, the type of which is specified by overriding the
session_attributes_cls
class attribute. The FSM is specified by a list of
parameter-less methods. Consider the following method:
@with_transitions(
{
'trigger': NEW_SEARCH,
'source': '*',
'prepare': 'm_search',
'conditions': 'm_has_result_and_query'
},
{
'trigger': NTH_SKILL,
'source': '*',
'conditions': 'm_has_nth',
'after': 'm_set_nth'
},
{
'trigger': PREVIOUS_SKILL,
'source': '*',
'conditions': 'm_has_previous',
'after': 'm_set_previous'
},
{
'trigger': NEXT_SKILL,
'source': '*',
'conditions': 'm_has_next',
'after': 'm_set_next'
},
{
'trigger': amazon_intent.NO,
'source': 'has_result',
'conditions': 'm_has_next',
'after': 'm_set_next'
}
)
def has_result(self) -> response.Response:
"""Offer a preview of a skill"""
attributes = self.attributes
query = attributes.query
skill = attributes.skill
asked_for_speech = ''
if attributes.first_time_presenting_results:
asked_for_speech = _you_asked_for(query)
if attributes.number_of_hits == 1:
skill_position_speech = 'The only skill I found is'
else:
skill_position_speech = f'The {ENGLISH_NUMBERS[attributes.skill_cursor]} skill is'
if attributes.first_time_presenting_results:
if attributes.number_of_hits > 6:
num_hits = f'Here are the top {MAX_SKILLS} results.'
else:
num_hits = f'I found {len(attributes.skills)} skills.'
skill_position_speech = f'{num_hits} {skill_position_speech}'
return response.Response(
speech=f"{asked_for_speech} "
f" {skill_position_speech} {_get_verbal_skill(skill)}."
f" {HEAR_MORE}",
card=f"Search for {query}",
card_content=f"""
Top result: {skill.name}
{_get_highlights(skill)}
""",
reprompt=DEFAULT_PROMPT
)
Each method encodes the following:
- The name of the method is also the name of a state (
describing
) in the FSM. - The method may be decorated with one or several transitions, using
with_transitions
decorators. Transitions can be inbound (source
needs to be specified) or outbound (dest
needs to be specified). - Each method returns a
Response
object which is sent to Alexa. - Transitions can be specified with
prepare
andconditions
attributes. See https://github.com/tyarkoni/transitions for detailed documentations. The values of these attributes are parameter-less methods of thePolicy
class. - The
prepare
methods are responsible for "actions" of the FSM such as querying a database. Theafter
methods are responsible for updating the state after the transition completes. They are the only methods responsible for side-effects, e.g. modifying the attributes of the states. This design facilitates ease of debugging.
Policy
Policy
is the class that holds everything together. It contains a reference to a States
object, the type of which is specified by overriding the states_cls
class attribute. A Policy
object initializes itself by constructing a FSM based on the States
type. Policy
class
contains the following key methods:
handle
takes an Alexa request, parses it, and hands over all intent requests toexecute
method.execute
updates the policy's internal state with the request's details (intent, slots, session attributes), then callstrigger
to make the state transition. It then looks up the corresponding response generating methods of theStates
class to generate a response for Alexa.initialize
will initialize a policy without any request.validate
performs validation of a policy object based onPolicy
class definition and a intent schema json file. It looks for intents that are not handled, invalid source/dest/prepare specifications, and unreachable states. The test intest_skillsearch.py
performs such validation as a test ofalexafsm
.
The Alexa skill search skill in the tests
directory also contains a Flask-based server that shows
how to use Policy
in five lines of code:
@app.route('/', methods=['POST'])
def main():
req = flask_request.json
policy = Policy.initialize()
return json.dumps(policy.handle(req, settings.vi)).encode('utf-8')
Other Tools
alexafsm
supports validation, graph visualization, and printing of the FSM.
Validation
Simply initialize a Policy
before calling validate
. This function takes as
input the path to the skill's Alexa intent schema json file and performs the
following checks:
- All Alexa intents have corresponding events/triggers in the FSM.
- All states have either inbound or outbound transitions.
- All transitions are specified with valid source and destination states.
- All conditions and prepare actions are handled with methods in the
Policy
class.
Change Detection with Record and Playback
When making code changes that are not supposed to impact a skill's dialog logic, we may want a tool
to check that the skill's logic indeed stay the same. This is done by first recording
(SkillSettings().record = True
) one or several sessions, making the code change, then checking
if the changed code still produces the same set of dialogs (SkillSettings().playback = True
).
During playback, calls to databases such as ElasticSearch can be fulfilled from data read from files
generated during the recording. This is done by decorating the database call with recordable
function. See the ElasticSearch call
in Skill Search for an example usage.
Graph Visualization
alexafsm
uses the transitions
library's API to draw the FSM graph. For example,
the skill search skill's FSM can be visualized using the graph.py.
invoked from graph.sh.
The resulting graph is displayed follow:
Graph Printout
For complex graphs, it may be easier to inspect the FSM in text format. Use the
print_machine
method to accomplish this. The output for the skill search skill is
below:
Machine states:
bad_navigate, describe_ratings, describing, exiting, has_result, helping, initial, is_that_all, no_query_search, no_result, search_prompt
Events and transitions:
Event: NthSkill
Source: bad_navigate
bad_navigate -> bad_navigate, conditions: ['m_has_nth']
bad_navigate -> has_result, conditions: ['m_has_nth']
Source: describe_ratings
describe_ratings -> bad_navigate, conditions: ['m_has_nth']
describe_ratings -> has_result, conditions: ['m_has_nth']
Source: describing
describing -> bad_navigate, conditions: ['m_has_nth']
describing -> has_result, conditions: ['m_has_nth']
Source: exiting
exiting -> bad_navigate, conditions: ['m_has_nth']
exiting -> has_result, conditions: ['m_has_nth']
Source: has_result
has_result -> bad_navigate, conditions: ['m_has_nth']
has_result -> has_result, conditions: ['m_has_nth']
Source: helping
helping -> bad_navigate, conditions: ['m_has_nth']
helping -> has_result, conditions: ['m_has_nth']
Source: initial
initial -> bad_navigate, conditions: ['m_has_nth']
initial -> has_result, conditions: ['m_has_nth']
Source: is_that_all
is_that_all -> bad_navigate, conditions: ['m_has_nth']
is_that_all -> has_result, conditions: ['m_has_nth']
Source: no_query_search
no_query_search -> bad_navigate, conditions: ['m_has_nth']
no_query_search -> has_result, conditions: ['m_has_nth']
Source: no_result
no_result -> bad_navigate, conditions: ['m_has_nth']
no_result -> has_result, conditions: ['m_has_nth']
Source: search_prompt
search_prompt -> bad_navigate, conditions: ['m_has_nth']
search_prompt -> has_result, conditions: ['m_has_nth']
Event: PreviousSkill
Source: bad_navigate
bad_navigate -> bad_navigate, conditions: ['m_has_previous']
bad_navigate -> has_result, conditions: ['m_has_previous']
Source: describe_ratings
describe_ratings -> bad_navigate, conditions: ['m_has_previous']
describe_ratings -> has_result, conditions: ['m_has_previous']
Source: describing
describing -> bad_navigate, conditions: ['m_has_previous']
describing -> has_result, conditions: ['m_has_previous']
Source: exiting
exiting -> bad_navigate, conditions: ['m_has_previous']
exiting -> has_result, conditions: ['m_has_previous']
Source: has_result
has_result -> bad_navigate, conditions: ['m_has_previous']
has_result -> has_result, conditions: ['m_has_previous']
Source: helping
helping -> bad_navigate, conditions: ['m_has_previous']
helping -> has_result, conditions: ['m_has_previous']
Source: initial
initial -> bad_navigate, conditions: ['m_has_previous']
initial -> has_result, conditions: ['m_has_previous']
Source: is_that_all
is_that_all -> bad_navigate, conditions: ['m_has_previous']
is_that_all -> has_result, conditions: ['m_has_previous']
Source: no_query_search
no_query_search -> bad_navigate, conditions: ['m_has_previous']
no_query_search -> has_result, conditions: ['m_has_previous']
Source: no_result
no_result -> bad_navigate, conditions: ['m_has_previous']
no_result -> has_result, conditions: ['m_has_previous']
Source: search_prompt
search_prompt -> bad_navigate, conditions: ['m_has_previous']
search_prompt -> has_result, conditions: ['m_has_previous']
Event: NextSkill
Source: bad_navigate
bad_navigate -> bad_navigate, conditions: ['m_has_next']
bad_navigate -> has_result, conditions: ['m_has_next']
Source: describe_ratings
describe_ratings -> bad_navigate, conditions: ['m_has_next']
describe_ratings -> has_result, conditions: ['m_has_next']
Source: describing
describing -> bad_navigate, conditions: ['m_has_next']
describing -> has_result, conditions: ['m_has_next']
Source: exiting
exiting -> bad_navigate, conditions: ['m_has_next']
exiting -> has_result, conditions: ['m_has_next']
Source: has_result
has_result -> bad_navigate, conditions: ['m_has_next']
has_result -> has_result, conditions: ['m_has_next']
Source: helping
helping -> bad_navigate, conditions: ['m_has_next']
helping -> has_result, conditions: ['m_has_next']
Source: initial
initial -> bad_navigate, conditions: ['m_has_next']
initial -> has_result, conditions: ['m_has_next']
Source: is_that_all
is_that_all -> bad_navigate, conditions: ['m_has_next']
is_that_all -> has_result, conditions: ['m_has_next']
Source: no_query_search
no_query_search -> bad_navigate, conditions: ['m_has_next']
no_query_search -> has_result, conditions: ['m_has_next']
Source: no_result
no_result -> bad_navigate, conditions: ['m_has_next']
no_result -> has_result, conditions: ['m_has_next']
Source: search_prompt
search_prompt -> bad_navigate, conditions: ['m_has_next']
search_prompt -> has_result, conditions: ['m_has_next']
Event: AMAZON.NoIntent
Source: has_result
has_result -> bad_navigate, conditions: ['m_has_next']
has_result -> has_result, conditions: ['m_has_next']
Source: describe_ratings
describe_ratings -> is_that_all
Source: describing
describing -> search_prompt
Source: is_that_all
is_that_all -> search_prompt
Event: DescribeRatings
Source: bad_navigate
bad_navigate -> describe_ratings, conditions: ['m_has_result']
Source: describe_ratings
describe_ratings -> describe_ratings, conditions: ['m_has_result']
Source: describing
describing -> describe_ratings, conditions: ['m_has_result']
Source: exiting
exiting -> describe_ratings, conditions: ['m_has_result']
Source: has_result
has_result -> describe_ratings, conditions: ['m_has_result']
Source: helping
helping -> describe_ratings, conditions: ['m_has_result']
Source: initial
initial -> describe_ratings, conditions: ['m_has_result']
Source: is_that_all
is_that_all -> describe_ratings, conditions: ['m_has_result']
Source: no_query_search
no_query_search -> describe_ratings, conditions: ['m_has_result']
Source: no_result
no_result -> describe_ratings, conditions: ['m_has_result']
Source: search_prompt
search_prompt -> describe_ratings, conditions: ['m_has_result']
Event: AMAZON.YesIntent
Source: has_result
has_result -> describing
Source: describe_ratings
describe_ratings -> describing
Source: describing
describing -> exiting
Source: is_that_all
is_that_all -> exiting
Event: AMAZON.CancelIntent
Source: no_result
no_result -> exiting
Source: search_prompt
search_prompt -> exiting
Source: is_that_all
is_that_all -> exiting
Source: bad_navigate
bad_navigate -> exiting
Source: no_query_search
no_query_search -> exiting
Source: describing
describing -> is_that_all
Source: has_result
has_result -> is_that_all
Source: describe_ratings
describe_ratings -> is_that_all
Source: initial
initial -> search_prompt
Source: helping
helping -> search_prompt
Event: AMAZON.StopIntent
Source: no_result
no_result -> exiting
Source: search_prompt
search_prompt -> exiting
Source: is_that_all
is_that_all -> exiting
Source: bad_navigate
bad_navigate -> exiting
Source: no_query_search
no_query_search -> exiting
Source: describing
describing -> is_that_all
Source: has_result
has_result -> is_that_all
Source: describe_ratings
describe_ratings -> is_that_all
Source: initial
initial -> search_prompt
Source: helping
helping -> search_prompt
Event: NewSearch
Source: bad_navigate
bad_navigate -> exiting, conditions: ['m_searching_for_exit']
bad_navigate -> has_result, prepare: ['m_search'], conditions: ['m_has_result_and_query']
bad_navigate -> no_query_search, conditions: ['m_no_query_search']
bad_navigate -> no_result, prepare: ['m_search'], conditions: ['m_no_result']
Source: describe_ratings
describe_ratings -> exiting, conditions: ['m_searching_for_exit']
describe_ratings -> has_result, prepare: ['m_search'], conditions: ['m_has_result_and_query']
describe_ratings -> no_query_search, conditions: ['m_no_query_search']
describe_ratings -> no_result, prepare: ['m_search'], conditions: ['m_no_result']
Source: describing
describing -> exiting, conditions: ['m_searching_for_exit']
describing -> has_result, prepare: ['m_search'], conditions: ['m_has_result_and_query']
describing -> no_query_search, conditions: ['m_no_query_search']
describing -> no_result, prepare: ['m_search'], conditions: ['m_no_result']
Source: exiting
exiting -> exiting, conditions: ['m_searching_for_exit']
exiting -> has_result, prepare: ['m_search'], conditions: ['m_has_result_and_query']
exiting -> no_query_search, conditions: ['m_no_query_search']
exiting -> no_result, prepare: ['m_search'], conditions: ['m_no_result']
Source: has_result
has_result -> exiting, conditions: ['m_searching_for_exit']
has_result -> has_result, prepare: ['m_search'], conditions: ['m_has_result_and_query']
has_result -> no_query_search, conditions: ['m_no_query_search']
has_result -> no_result, prepare: ['m_search'], conditions: ['m_no_result']
Source: helping
helping -> exiting, conditions: ['m_searching_for_exit']
helping -> has_result, prepare: ['m_search'], conditions: ['m_has_result_and_query']
helping -> no_query_search, conditions: ['m_no_query_search']
helping -> no_result, prepare: ['m_search'], conditions: ['m_no_result']
Source: initial
initial -> exiting, conditions: ['m_searching_for_exit']
initial -> has_result, prepare: ['m_search'], conditions: ['m_has_result_and_query']
initial -> no_query_search, conditions: ['m_no_query_search']
initial -> no_result, prepare: ['m_search'], conditions: ['m_no_result']
Source: is_that_all
is_that_all -> exiting, conditions: ['m_searching_for_exit']
is_that_all -> has_result, prepare: ['m_search'], conditions: ['m_has_result_and_query']
is_that_all -> no_query_search, conditions: ['m_no_query_search']
is_that_all -> no_result, prepare: ['m_search'], conditions: ['m_no_result']
Source: no_query_search
no_query_search -> exiting, conditions: ['m_searching_for_exit']
no_query_search -> has_result, prepare: ['m_search'], conditions: ['m_has_result_and_query']
no_query_search -> no_query_search, conditions: ['m_no_query_search']
no_query_search -> no_result, prepare: ['m_search'], conditions: ['m_no_result']
Source: no_result
no_result -> exiting, conditions: ['m_searching_for_exit']
no_result -> has_result, prepare: ['m_search'], conditions: ['m_has_result_and_query']
no_result -> no_query_search, conditions: ['m_no_query_search']
no_result -> no_result, prepare: ['m_search'], conditions: ['m_no_result']
Source: search_prompt
search_prompt -> exiting, conditions: ['m_searching_for_exit']
search_prompt -> has_result, prepare: ['m_search'], conditions: ['m_has_result_and_query']
search_prompt -> no_query_search, conditions: ['m_no_query_search']
search_prompt -> no_result, prepare: ['m_search'], conditions: ['m_no_result']
Event: AMAZON.HelpIntent
Source: bad_navigate
bad_navigate -> helping
Source: describe_ratings
describe_ratings -> helping
Source: describing
describing -> helping
Source: exiting
exiting -> helping
Source: has_result
has_result -> helping
Source: helping
helping -> helping
Source: initial
initial -> helping
Source: is_that_all
is_that_all -> helping
Source: no_query_search
no_query_search -> helping
Source: no_result
no_result -> helping
Source: search_prompt
search_prompt -> helping