A simple Paxos implementation for study.

paxos.py

"""
A simple Paxos implementation for study.
"""

from collections import Counter

class Proposer:

    def __init__(self, acceptors):
        self.acceptors = acceptors
        self.number = 0
        self.value = 'proposal value'
        self.preparing_acceptors = []

    def send_prepare_requests(self):
        print('Start sending prepare requests.')

        self.preparing_acceptors = []
        highest_res_num = -1

        for acceptor in acceptors:
            print('  Send a prepare request to ' + str(acceptor) +
            ' with no = ' + str(self.number) + '.')

            try:
                responce = acceptor.prepare(self.number)
            except IOError:
                print('  Failed to send a prepare request to ' + str(acceptor) + '.')
                continue

            self.preparing_acceptors.append(acceptor)

            res_number = responce[0]
            res_value = responce[1]

            if res_number > highest_res_num:
                highest_res_num = number
                # Remember the highest-numbered proposal among the responces.
                self.value = value

        num_acceptors = len(self.acceptors)
        num_preparing = len(self.preparing_acceptors)

        print(str(num_preparing) + ' / ' + str(num_acceptors) + ' are preparing.')

        if (num_preparing < num_acceptors // 2 + 1):
            print('Acceptors that responded to a prepare request are not majority.')
            return

        print('Finish sending prepare requests.')

    def send_accept_requests(self):
        print('Start to send accept requests.')

        for acceptor in self.preparing_acceptors:
            print('  Send a accept request to ' + str(acceptor) +
                  ' with no = ' + str(self.number) +
                  ', value = "' + str(self.value) + '".')
            try:
                acceptor.accept(self.number, self.value)
            except IOError:
                print('  Failed to send a accept request to ' + str(acceptor))

        print('Finish sending accept requests.')

class Acceptor:

    def __init__(self, name, learners):
        self.name = name
        self.learners = learners
        self.prepared_number = -1
        self.accepted_number = -1
        self.accepted_value = None

    def __str__(self):
        return self.name

    def prepare(self, proposal_number):
        if proposal_number <= self.prepared_number:
            return None

        self.prepared_number = proposal_number

        # If not accept any proposal yet, return (-1, None)
        return (self.accepted_number, self.accepted_value)

    def accept(self, proposal_number, proposal_value):
        if proposal_number < self.prepared_number:
            return

        self.accepted_number = proposal_number
        self.accepted_value = proposal_value

        for learner in self.learners:
            learner.learn_accepted_value(
                self.name, proposal_number, proposal_value)

class Learner:

    def __init__(self, num_acceptors):
        self.num_acceptors = num_acceptors
        self.accepting_acceptors = []
        self.accepted_value = []

    def learn_accepted_value(
            self, name, proposal_number, proposal_value):
        print('  ' + str(name) + ' accepted "' +
              str(proposal_value) + '".')

        self.accepting_acceptors.append(name)
        self.accepted_value.append(proposal_value)

    def get_chosen_value(self):
        most_common, num_most_common = \
            Counter(self.accepted_value).most_common(1)[0]

        if num_most_common < num_acceptors // 2 + 1:
            print('The mostly accepted value is "' + str(most_common) + '", but not majority.')
            return None

        print('The chosen value is "' + str(most_common) + '".')
        return most_common

if __name__ == '__main__':
    num_acceptors = 2

    learner = Learner(2)

    acceptors = []

    for i in range(num_acceptors):
        name = 'a' + str(i)
        learners = [learner]
        acceptor = Acceptor(name, learners)
        acceptors.append(acceptor)

    proposer = Proposer(acceptors)

    proposer.send_prepare_requests()
    proposer.send_accept_requests()

    learner.get_chosen_value()

hey Brother,
can you help me how to use this code