Subversion Repositories programming

#!/usr/bin/env python

# Copyright: Ira W. Snyder

# Start Date: 2005-10-08

# End Date:

# License: Public Domain

#

# Changelog Follows:

# - 2005-10-16

# - Implemented the nfa class. It's mostly complete at this point.

# - E() function works for circular loops now.

# - Made the nfa.__next_states() function always return a valid reference

#   to a list in the dictionary. This means you should NEVER use

#   self.trans_func[(state, letter)] in code anywhere now :)

# - Final states are now checked for validity.

#

################################################################################

# IMPORTANT NOTES

################################################################################

################################################################################

import sys, string

class nfa:

    """Implements a Non-Deterministic Finite Automaton"""

    def __init__(self):

        self.trans_func = {}

        self.num_states = 0

        self.final_states = []

        self.initial_state = 0

        self.possible_letters = []

        self.dfa_table = []

    def __state_in_range(self, state):

        """Check if a given state is in the acceptable range"""

        try:

            temp = int(state)

        except (TypeError, ValueError):

            return False

        if temp >= 0 and temp < self.num_states:

            return True

        return False

    def __input_num_states(self):

        """Get the number of states this automaton will have"""

        done = False

        while not done:

            num_states = raw_input('How many states in this automaton: ')

            try:

                self.num_states = int(num_states)

                done = True

            except (TypeError, ValueError):

                print 'Bad input, not an integer, try again'

                print

    def __input_final_states(self):

        """Get final states for this automaton"""

        print 'Enter final states on one line, seperated by spaces'

        done = False

        while not done:

            final_states = raw_input('Final states: ')

            bad_data = False

            for i in final_states.split():

                if not self.__state_in_range(i):

                    print 'State %s out of range. All input discarded.' % (i, )

                    print 'Try again please'

                    print

                    bad_data = True

                    break

            # if we left the for loop with bad data

            if bad_data:

                continue

            # all data is good

            for i in final_states.split():

                if self.__state_in_range(i):

                    self.final_states.append(int(i))

            done = True

    def __input_all_edges(self):

        """Read all of the edges for this automaton"""

        print 'Edges take the form "from HERE, by LETTER, to THERE"'

        print 'Enter something like: "1 a 1" to represent the following'

        print 'from q1, by a, go to q1'

        print

        print 'Conditions:'

        print '1. Blank line to end'

        print '2. ^ is the empty string'

        done = False

        while not done:

            edge = raw_input('Edge: ')

            if len(edge) == 0:

                done = True

                continue

            if len(edge.split()) != 3:

                print 'Bad edge entered'

                print

                continue

            (cur_st, letter, next_st) = edge.split()

            # Make sure the states entered are in range

            if self.__state_in_range(cur_st) and self.__state_in_range(next_st):

                new_state = False

                cur_st = int(cur_st)

                next_st = int(next_st)

                # Add the state to the list if it's not there already

                if next_st not in self.__next_states(cur_st, letter):

                    self.__next_states(cur_st, letter).append(next_st)

            else:

                print 'Invalid current or next state entered'

                print

                continue

    def __input_automaton(self):

        """Read this entire automaton's input"""

        self.__input_num_states()

        self.__input_final_states()

        self.__input_all_edges()

        # Make sure to visit all '^' states (to make printing easier, later)

        for i in range(self.num_states):

            self.__E(i)

    def main_menu(self):

        #NOTE: All of this code is not what it's supposed to be.

        #      It is for TESTING ONLY.

        #

        #TODO: Generate a menu :)

        self.__input_automaton()

        print

        print

        print 'Initial State: %s' % (0, )

        print

        self.__generate_dfa_table()

        self.__print_dfa_table()

    def __print_dfa_table(self):

        header1 = '%-8s%-8s%-20s' % ('Final', 'Number', 'NFA Equiv')

        header2 = ''

        for l in self.possible_letters:

            header2 = '%s%-4s' % (header2, l)

        heading = '%s %s' % (header1, header2)

        hdr_line = ''

        for i in range(len(heading)):

            hdr_line = '%s-' % (hdr_line, )

        print heading

        print hdr_line

        for rec in self.dfa_table:

            line1 = '%-8s%-8s%-20s' % (rec[0], rec[1], rec[2])

            line2 = ''

            for l in range(len(self.possible_letters)):

                line2 = '%s%-4s' % (line2, rec[l+3])

            print '%s %s' % (line1, line2)

    def __next_states(self, state, letter):

        """Return the next states for the key (state, letter)"""

        try:

            next = self.trans_func[(state, letter)]

        except KeyError:

            # Create a new empty list for this state if it doesn't exist yet

            next = self.trans_func[(state, letter)] = []

        if letter == '^' and state not in next:

            next.append(state)

        return next

    def __E(self, state, letter='^', storage=None, visited=None):

        """Calculate E(state) and return it. This handles circular E()

        calculations."""

        # Work around weird mutable default argument stuff

        if storage is None:

            storage = []

        # Work around weird mutable default argument stuff

        if visited is None:

            visited = []

        # Find all of the direct next states that we can get to by

        # the empty string, and append anything that is not already there

        for i in self.__next_states(state, letter):

            if i not in storage:

                storage.append(i)

        # Visit everything in storage that has not been visited already

        for i in storage:

            if i not in visited:

                visited.append(i)

                temp = self.__E(i, letter, storage, visited)

                # Avoid duplicating things in storage

                for j in temp:

                    if j not in storage:

                        storage.append(j)

        return storage

    def __by_letter(self, states, letter):

        """Returns a list of states to where you can go from a list of states,

        by a certain letter"""

        from_states = []

        for s in states:

            from_states.extend(self.__E(s))

        from_states = self.__unique_sort(from_states)

        new_states = []

        for s in from_states:

            new_states.extend(self.__next_states(s, letter))

        new_states = self.__unique_sort(new_states)

        return new_states

    def __unique_sort(self, li):

        """Make sure everything in a list is unique, and then sort it"""

        newlist = []

        for i in li:

            if i not in newlist:

                newlist.append(i)

        newlist.sort()

        return newlist

    def __is_final_state(self, state):

        """Check if a state is a final state."""

        if state in self.final_states:

            return True

        return False

    def __is_list_final(self, states):

        """Check if at least one state in the list "states" is final"""

        for s in states:

            if self.__is_final_state(s):

                return True

        return False

    def __get_temp_record(self, num_letters):

        blank = None

        return [blank for i in range(num_letters + 3)]

    def __generate_dfa_table(self):

        # get the list of all letters

        possible_letters = []

        for (state, letter) in self.trans_func.keys():

            if letter not in possible_letters and letter != '^':

                possible_letters.append(letter)

        self.possible_letters = possible_letters

        #prime the dfa table

        self.make_basic_record(self.__E(0))

        while self.find_unresolved_letter() != (-1, -1): #loop until we've resolved everything

            (record, letter_pos) = self.find_unresolved_letter()

            self.resolve_letter(record, letter_pos)

    def resolve_letter(self, record, letter_pos):

        fromstates = self.dfa_table[record][2]

        tostates = []

        for s in fromstates:

            tostates.extend(self.__next_states(s, self.possible_letters[letter_pos-3]))

        self.dfa_table[record][letter_pos] = self.make_basic_record(tostates)

    def find_unresolved_letter(self): # WORKING

        """Returns an index pair of an unresolved letter that exists in the dfa_table.

        If there are no more letters, return (-1, -1)"""

        for i in range(len(self.dfa_table)):

            for j in range(len(self.possible_letters)):

                if self.dfa_table[i][j+3] == None:

                    return (i, j+3)

        return (-1, -1)

    def make_basic_record(self, from_states):

        if self.dfa_state_exists(from_states) == -1: #doesn't exist

            temp_record = self.__get_temp_record(len(self.possible_letters))

            recordnum = len(self.dfa_table)

            temp_record[1] = recordnum

            temp_record[2] = self.__unique_sort(from_states)

            temp_record[0] = self.__is_list_final(from_states)

            self.dfa_table.append(temp_record)

        # always return a re-call of the function. This will not fail, since a new

        # record is added above if a record does not already exist.

        return self.dfa_state_exists(from_states)

    def dfa_state_exists(self, from_states):

        """Find out if this state already exists in the dfa table.

        If it does exist, return it's dfa state name.

        If it does not exist, return -1"""

        sorted_states = self.__unique_sort(from_states)

        for i in range(len(self.dfa_table)):

            if self.dfa_table[i][2] == sorted_states:

                return self.dfa_table[i][1]

        return -1

if __name__ == '__main__':

    automaton = nfa()

    automaton.main_menu()