I recently came across this code on the internet and I'm having a very hard time understand how it works. I was hoping someone could comment the code a bit in order to help me learn it better? I understand most of it, but get lost when any of the code deals with the "handler" parts. (ie. why does the author feed multiple "handlers" into a dictionary?) Anyway here it is:
class StateMachine:
def __init__(self):
self.handlers = {}
self.endStates = []
self.startState = None
def add_state(self, name, handler, end_state=0):
self.handlers[name] = handler
if end_state:
self.endStates.append(name)
def set_start(self, name):
self.startState = name
def run(self, content):
if self.startState in self.handlers:
handler = self.handlers[self.startState]
else:
raise "InitializationError", ".set_start() has to be called before .run()"
if not self.endStates:
raise "InitializationError", "at least one state must be an end_state"
oldState = self.startState
while 1:
(newState, content) = handler(content, oldState)
if newState in self.endStates:
print "reached ", newState, "which is an end state"
break
else:
handler = self.handlers[newState]
oldState = newState
from statemachine import StateMachine
positive_adjectives = ["great","super", "fun", "entertaining", "easy"]
negative_adjectives = ["boring", "difficult", "ugly", "bad"]
def transitions(txt, state):
splitted_txt = txt.split(None,1)
word, txt = splitted_txt if len(splitted_txt) > 1 else (txt,"")
if state == "Start":
if word == "Python":
newState = "Python_state"
else:
newState = "error_state"
return (newState, txt)
elif state == "Python_state":
if word == "is":
newState = "is_state"
else:
newState = "error_state"
return (newState, txt)
elif state == "is_state":
if word == "not":
newState = "not_state"
elif word in positive_adjectives:
newState = "pos_state"
elif word in negative_adjectives:
newState = "neg_state"
else:
newState = "error_state"
return (newState, txt)
elif state == "not_state":
if word in positive_adjectives:
newState = "neg_state"
elif word in negative_adjectives:
newState = "pos_state"
else:
newState = "error_state"
return (newState, txt)
if __name__== "__main__":
m = StateMachine()
m.add_state("Start", transitions)
m.add_state("Python_state", transitions)
m.add_state("is_state", transitions)
m.add_state("not_state", transitions)
m.add_state("neg_state", None, end_state=1)
m.add_state("pos_state", None, end_state=1)
m.add_state("error_state", None, end_state=1)
m.set_start("Start")
m.run("Python is great")
m.run("Python is difficult")
m.run("Perl is ugly")
