File: editdist.py

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#!/usr/bin/python

# see editdist.py --help for usage


import sys
import struct
import codecs
from optparse import OptionParser

usage_string = "usage: %prog [options] alphabet"

info_string = """
Produce an edit distance transducer in ATT format.

There are three ways to produce an edit distance transducer:

* giving the alphabet as a command line argument
* giving a file with specialized configuration syntax
* giving a transducer in optimized-lookup format to induce an alphabet
    (in this case only symbols with length 1 are considered)

These ways may be combined freely.

For the default case, all the desired transitions are generated with weight 1.0.
The alphabet is read from a string which contains all the (utf-8) characters
you want to use. Alternatively, an existing optimized-lookup transducer
can be supplied for reading the alphabet.

The specification file should be in the following format:
* First, an (optional) list of tokens separated by newlines
  All transitions involving these tokens that are otherwise unspecified
  are generated with weight 1.0. Symbol weights can be specified by appending
  a tab and a weight to the symbol. Transitions involving such a symbol
  will have the user-specified weight added to it.
* If you want to exclude symbols that may be induced from a transducer,
  add a leading ~ character to that line.
* If you want to specify transitions, insert a line with the content "@@"
  (without the quotes)
* In the following lines, specified transitions with the form
  FROM <TAB> TO <TAB> WEIGHT
  where FROM is the source token, TO is the destination token and WEIGHT is
  a nonnegative floating point number specifying the weight. By default,
  if only one transition involving FROM and TO is specified, the same WEIGHT
  will be used to specify the transition TO -> FROM (assuming that both are
  listed in the list of tokens).
* If the command line option to generate swaps is set, you can also specify swap
  weights with
  FROM,TO <TAB> TO,FROM <TAB> WEIGHT
  Again, unspecified swaps will be generated automatically with weight 1.0.
* Lines starting with ## are comments.

with d for distance and S for size of alphabet plus one
(for epsilon), expected output is a transducer in ATT format with
* Swapless:
** d + 1 states
** d*(S^2 + S - 1) transitions
* Swapful:
** d*(S^2 - 3S + 3) + 1 states
** d*(3S^2 - 5S + 3) transitions
"""

# Some utility classes

class Header:
    """Read and provide interface to header"""
    
    def __init__(self, file):
        bytes = file.read(5) # "HFST\0"
        if str(struct.unpack_from("<5s", bytes, 0)) == "('HFST\\x00',)":
            # just ignore any hfst3 header
            remaining = struct.unpack_from("<H", file.read(3), 0)[0]
            self.handle_hfst3_header(file, remaining)
            bytes = file.read(56) # 2 unsigned shorts, 4 unsigned ints and 9 uint-bools
        else:
            bytes = bytes + file.read(56 - 5)
        self.number_of_input_symbols             = struct.unpack_from("<H", bytes, 0)[0]
        self.number_of_symbols                   = struct.unpack_from("<H", bytes, 2)[0]
        self.size_of_transition_index_table      = struct.unpack_from("<I", bytes, 4)[0]
        self.size_of_transition_target_table     = struct.unpack_from("<I", bytes, 8)[0]
        self.number_of_states                    = struct.unpack_from("<I", bytes, 12)[0]
        self.number_of_transitions               = struct.unpack_from("<I", bytes, 16)[0]
        self.weighted                            = struct.unpack_from("<I", bytes, 20)[0] != 0
        self.deterministic                       = struct.unpack_from("<I", bytes, 24)[0] != 0
        self.input_deterministic                 = struct.unpack_from("<I", bytes, 28)[0] != 0
        self.minimized                           = struct.unpack_from("<I", bytes, 32)[0] != 0
        self.cyclic                              = struct.unpack_from("<I", bytes, 36)[0] != 0
        self.has_epsilon_epsilon_transitions     = struct.unpack_from("<I", bytes, 40)[0] != 0
        self.has_input_epsilon_transitions       = struct.unpack_from("<I", bytes, 44)[0] != 0
        self.has_input_epsilon_cycles            = struct.unpack_from("<I", bytes, 48)[0] != 0
        self.has_unweighted_input_epsilon_cycles = struct.unpack_from("<I", bytes, 52)[0] != 0

    def handle_hfst3_header(self, file, remaining):
        chars = struct.unpack_from("<" + str(remaining) + "c",
                                   file.read(remaining), 0)
        # assume the h3-header doesn't say anything surprising for now

class Alphabet:
    """Read and provide interface to alphabet"""

    def __init__(self, file, number_of_symbols):
        stderr_u8 = codecs.getwriter('utf-8')(sys.stderr)
        self.keyTable = [] # list of unicode objects, use foo.encode("utf-8") to print
        for x in range(number_of_symbols):
            symbol = ""
            while True:
                byte = file.read(1)
                if byte == '\0': # a symbol has ended
                    symbol = unicode(symbol, "utf-8")
                    if len(symbol) != 1:
                        stderr_u8.write("Ignored symbol " + symbol + "\n")
                    else:
                        self.keyTable.append(symbol)
                    break
                symbol += byte

class MyOptionParser(OptionParser):
    # This is needed to override the formatting of the help string
    def format_epilog(self, formatter):
        return self.epilog

parser = MyOptionParser(usage=usage_string, epilog=info_string)
parser.add_option("-e", "--epsilon", dest = "epsilon",
                  help = "specify symbol to use as epsilon, default is @0@",
                  metavar = "EPS")
parser.add_option("-d", "--distance", type = "int", dest = "distance",
                  help = "specify edit depth, default is 1",
                  metavar = "DIST")
parser.add_option("-s", "--swap", action = "store_true", dest="swap",
                  help = "generate swaps (as well as insertions and deletions)")
parser.add_option("", "--no-elim", action = "store_true", dest="no_elim",
                  help = "don't do redundancy elimination")
parser.add_option("-i", "--input", dest = "inputfile",
                  help = "optional file with special edit-distance syntax",
                  metavar = "INPUT")
parser.add_option("-a", "--alphabet", dest = "alphabetfile",
                  help = "read the alphabet from an existing optimized-lookup format transducer",
                  metavar = "ALPHABET")
parser.add_option("-v", "--verbose", action = "store_true", dest="verbose",
                  help = "print some diagnostics to standard error")
parser.set_defaults(epsilon = '@0@')
parser.set_defaults(distance = 1)
parser.set_defaults(swap = False)
parser.set_defaults(no_elim = False)
parser.set_defaults(verbose = False)
(options, args) = parser.parse_args()

alphabet = {}
exclusions = set()

if options.inputfile == None and options.alphabetfile == None \
        and len(args) == 0:
    print "Specify at least one of INPUT, ALPHABET or alphabet string"
    sys.exit()
if len(args) > 1:
    print "Too many options!"
    sys.exit()

if options.inputfile != None:
    try:
        inputfile = open(options.inputfile)
    except IOError:
        print "Couldn't open " + options.inputfile
        sys.exit()
    while True:
        line = unicode(inputfile.readline(), 'utf-8')
        if line in ("@@\n", ""):
            break
        if line.strip() != "":
            if line.startswith(u'##'):
                continue
            if len(line) > 1 and line.startswith(u'~'):
                exclusions.add(line[1:].strip())
                continue
            if '\t' in line:
                weight = float(line.split('\t')[1])
                symbol = linesplit('\t')[0]
            else:
                weight = 0.0
                symbol = line.strip("\n")
            alphabet[symbol] = weight

if len(args) == 1:
    for c in unicode(args[0], 'utf-8'):
        if c not in alphabet.keys() and c not in exclusions:
            alphabet[c] = 0.0
if options.alphabetfile != None:
    afile = open(options.alphabetfile, "rb")
    ol_header = Header(afile)
    ol_alphabet = Alphabet(afile, ol_header.number_of_symbols)
    for c in filter(lambda x: x.strip() != '', ol_alphabet.keyTable[:]):
        if c not in alphabet.keys() and c not in exclusions:
            alphabet[c] = 0.0
epsilon = unicode(options.epsilon, 'utf-8')
OTHER = u'@_UNKNOWN_SYMBOL_@'

def p(string): # stupid python, or possibly stupid me
    return string.encode('utf-8')

def maketrans(from_st, to_st, from_sy, to_sy, weight):
    return str(from_st) + "\t" + str(to_st) + "\t" + p(from_sy) + "\t" + p(to_sy) + "\t" + str(weight)

class Transducer:
    def __init__(self, alphabet, _other = OTHER, _epsilon = epsilon):
        self.alphabet = alphabet
        self.substitutions = {}
        self.swaps = {}
        self.other = _other
        self.epsilon = _epsilon
        self.swapstate = options.distance + 1
        self.skipstate = self.swapstate + 1
        self.transitions = []

    def process(self, specification):
        parts = specification.split('\t')
        if len(parts) != 3:
            raise ValueError("Got specification with " + str(len(parts)) +\
                                 " parts, expected 3:\n" + specification)
        weight = float(parts[2])
        if ',' in parts[0]:
            frompair = tuple(parts[0].split(','))
            topair = tuple(parts[1].split(','))
            if not (len(frompair) == len(topair) == 2):
                raise ValueError("Got swap-specification with incorrect number "
                                 "of comma separators:\n" + specification)
            if (frompair, topair) not in self.swaps:
                self.swaps[(frompair, topair)] = weight
        else:
            if not (parts[0], parts[1]) in self.substitutions:
                self.substitutions[(parts[0], parts[1])] = weight

    def generate(self):
        # for substitutions and swaps that weren't defined by the user,
        # generate standard subs and swaps
        if (self.other, self.epsilon) not in self.substitutions:
            self.substitutions[(self.other, self.epsilon)] = 1.0
        for symbol in self.alphabet.keys():
            if (self.other, symbol) not in self.substitutions:
                self.substitutions[(self.other, symbol)] = 1.0 + alphabet[symbol]
            if (self.epsilon, symbol) not in self.substitutions:
                self.substitutions[(self.epsilon, symbol)] = 1.0 + alphabet[symbol]
            if (symbol, self.epsilon) not in self.substitutions:
                self.substitutions[(symbol, self.epsilon)] = 1.0 + alphabet[symbol]
            for symbol2 in self.alphabet.keys():
                if symbol == symbol2: continue
                if ((symbol, symbol2), (symbol2, symbol)) not in self.swaps:
                    if ((symbol2, symbol), (symbol, symbol2)) in self.swaps:
                        self.swaps[((symbol, symbol2), (symbol2, symbol))] = self.swaps[((symbol2, symbol), (symbol, symbol2))]
                    else:
                        self.swaps[((symbol, symbol2), (symbol2, symbol))] = 1.0 + alphabet[symbol] + alphabet[symbol2]
                if (symbol, symbol2) not in self.substitutions:
                    if (symbol2, symbol) in self.substitutions:
                        self.substitutions[(symbol, symbol2)] = self.substitutions[(symbol2, symbol)]
                    else:
                        self.substitutions[(symbol, symbol2)] = 1.0 + alphabet[symbol] + alphabet[symbol2]

    def next_special(self, state):
        if state == "swap":
            self.swapstate += 1
            while self.swapstate == self.skipstate:
                self.swapstate += 1
        elif state == "skip":
            self.skipstate += 1
            while self.skipstate == self.swapstate:
                self.skipstate += 1
        else:
            raise Exception

    def make_identities(self, state, nextstate = None):
        if nextstate is None:
            nextstate = state
        ret = []
        for symbol in self.alphabet.keys():
            if symbol not in (self.epsilon, self.other):
                ret.append(maketrans(state, nextstate, symbol, symbol, 0.0))
        return ret

    def make_swaps(self, state, nextstate = None):
        if nextstate is None:
            nextstate = state + 1
        ret = []
        if options.swap:
            for swap in self.swaps:
                ret.append(maketrans(state, self.swapstate, swap[0][0], swap[0][1], self.swaps[swap]))
                ret.append(maketrans(self.swapstate, nextstate, swap[1][0], swap[1][1], 0.0))
                self.next_special("swap")
        return ret

    # for substitutions, we try to eliminate redundancies by refusing to do
    # deletion right after insertion and insertion right after deletion
    def make_substitutions(self, state, nextstate = None):
        if nextstate is None:
            nextstate = state + 1
        ret = []
        for sub in self.substitutions:
            if (nextstate + 1 >= options.distance) or options.no_elim:
                ret.append(maketrans(state, nextstate, sub[0], sub[1], self.substitutions[sub]))
            elif sub[1] is self.epsilon: # deletion
                ret.append(maketrans(state, self.skipstate, sub[0], sub[1], self.substitutions[sub]))
                ret += self.make_identities(self.skipstate, nextstate)
                ret += self.make_swaps(self.skipstate, nextstate + 1)
                for sub2 in self.substitutions:
                    # after deletion, refuse to do insertion
                    if sub2[0] != self.epsilon:
                        ret.append(maketrans(self.skipstate, nextstate + 1, sub2[0], sub2[1], self.substitutions[sub2]))
                self.next_special("skip")
            elif sub[0] is self.epsilon: # insertion
                ret.append(maketrans(state, self.skipstate, sub[0], sub[1], self.substitutions[sub]))
                ret += self.make_identities(self.skipstate, nextstate)
                ret += self.make_swaps(self.skipstate, nextstate + 1)
                for sub2 in self.substitutions:
                    # after insertion, refuse to do deletion
                    if sub2[1] != self.epsilon:
                        ret.append(maketrans(self.skipstate, nextstate + 1, sub2[0], sub2[1], self.substitutions[sub2]))
                self.next_special("skip")
            else:
                ret.append(maketrans(state, nextstate, sub[0], sub[1], self.substitutions[sub]))
        return ret

    def make_transitions(self):
        for state in range(options.distance):
            self.transitions.append(str(state + 1) + "\t0.0") # final states
            self.transitions += self.make_identities(state)
            self.transitions += self.make_substitutions(state)
            self.transitions += self.make_swaps(state)
        self.transitions += self.make_identities(options.distance)

transducer = Transducer(alphabet)

if options.inputfile != None:
    while True:
        line = inputfile.readline()
        if line.startswith('##'):
            continue
        if line == "\n":
            continue
        if line == "":
            break
        transducer.process(unicode(line, "utf-8"))

transducer.generate()
transducer.make_transitions()
for transition in transducer.transitions:
    print transition

stderr_u8 = codecs.getwriter('utf-8')(sys.stderr)

if options.verbose:
    stderr_u8.write("\n" + str(max(transducer.skipstate, transducer.swapstate)) + " states and " + str(len(transducer.transitions)) + " transitions written for\n"+
                     "distance " + str(options.distance) + " and base alphabet size " + str(len(transducer.alphabet)) +"\n\n")
    stderr_u8.write("The alphabet was:\n")
    for symbol, weight in alphabet.iteritems():
        stderr_u8.write(symbol + "\t" + str(weight) + "\n")
    if len(exclusions) != 0:
        stderr_u8.write("The exclusions were:\n")
        for symbol in exclusions:
            stderr_u8.write(symbol + "\n")