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spark.py

#  Copyright (c) 1998-2000 John Aycock
#  
#  Permission is hereby granted, free of charge, to any person obtaining
#  a copy of this software and associated documentation files (the
#  "Software"), to deal in the Software without restriction, including
#  without limitation the rights to use, copy, modify, merge, publish,
#  distribute, sublicense, and/or sell copies of the Software, and to
#  permit persons to whom the Software is furnished to do so, subject to
#  the following conditions:
#  
#  The above copyright notice and this permission notice shall be
#  included in all copies or substantial portions of the Software.
#  
#  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
#  EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
#  MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
#  IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
#  CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
#  TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
#  SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

__version__ = 'SPARK-0.6.1'

import re
import sys

def _namelist(instance):
    namelist, namedict, classlist = [], {}, [instance.__class__]
    for c in classlist:
        for b in c.__bases__:
            classlist.append(b)
        for name in dir(c):
            if name not in namedict:
                namelist.append(name)
                namedict[name] = 1
    return namelist

class GenericScanner:
    def __init__(self):
        pattern = self.reflect()
        self.re = re.compile(pattern, re.VERBOSE)

        self.index2func = {}
        for name, number in self.re.groupindex.items():
            self.index2func[number-1] = getattr(self, 't_' + name)

    def makeRE(self, name):
        doc = getattr(self, name).__doc__
        rv = '(?P<%s>%s)' % (name[2:], doc)
        return rv

    def reflect(self):
        rv = []
        for name in _namelist(self):
            if name[:2] == 't_' and name != 't_default':
                rv.append(self.makeRE(name))

        rv.append(self.makeRE('t_default'))
        return '|'.join(rv)

    def error(self, s, pos):
        print "Lexical error at position %s" % pos
        raise SystemExit

    def tokenize(self, s):
        pos = 0
        n = len(s)
        while pos < n:
            m = self.re.match(s, pos)
            if m is None:
                self.error(s, pos)

            groups = m.groups()
            for i in range(len(groups)):
                if groups[i] and i in self.index2func:
                    self.index2func[i](groups[i])
            pos = m.end()

    def t_default(self, s):
        r'( . | \n )+'
        pass

class GenericParser:
    def __init__(self, start):
        self.rules = {}
        self.rule2func = {}
        self.rule2name = {}
        self.collectRules()
        self.startRule = self.augment(start)
        self.ruleschanged = 1

    _START = 'START'
    _EOF = 'EOF'

    #
    #  A hook for GenericASTBuilder and GenericASTMatcher.
    #
    def preprocess(self, rule, func):   return rule, func

    def addRule(self, doc, func):
        rules = doc.split()

        index = []
        for i in range(len(rules)):
            if rules[i] == '::=':
                index.append(i-1)
        index.append(len(rules))

        for i in range(len(index)-1):
            lhs = rules[index[i]]
            rhs = rules[index[i]+2:index[i+1]]
            rule = (lhs, tuple(rhs))

            rule, fn = self.preprocess(rule, func)

            if lhs in self.rules:
                self.rules[lhs].append(rule)
            else:
                self.rules[lhs] = [ rule ]
            self.rule2func[rule] = fn
            self.rule2name[rule] = func.__name__[2:]
        self.ruleschanged = 1

    def collectRules(self):
        for name in _namelist(self):
            if name[:2] == 'p_':
                func = getattr(self, name)
                doc = func.__doc__
                self.addRule(doc, func)

    def augment(self, start):
        #
        #  Tempting though it is, this isn't made into a call
        #  to self.addRule() because the start rule shouldn't
        #  be subject to preprocessing.
        #
        startRule = (self._START, ( start, self._EOF ))
        self.rule2func[startRule] = lambda args: args[0]
        self.rules[self._START] = [ startRule ]
        self.rule2name[startRule] = ''
        return startRule

    def makeFIRST(self):
        union = {}
        self.first = {}
        
        for rulelist in self.rules.values():
            for lhs, rhs in rulelist:
                if lhs not in self.first:
                    self.first[lhs] = {}

                if len(rhs) == 0:
                    self.first[lhs][None] = 1
                    continue

                sym = rhs[0]
                if sym not in self.rules:
                    self.first[lhs][sym] = 1
                else:
                    union[(sym, lhs)] = 1
        changes = 1
        while changes:
            changes = 0
            for src, dest in union.keys():
                destlen = len(self.first[dest])
                self.first[dest].update(self.first[src])
                if len(self.first[dest]) != destlen:
                    changes = 1

    #
    #  An Earley parser, as per J. Earley, "An Efficient Context-Free
    #  Parsing Algorithm", CACM 13(2), pp. 94-102.  Also J. C. Earley,
    #  "An Efficient Context-Free Parsing Algorithm", Ph.D. thesis,
    #  Carnegie-Mellon University, August 1968, p. 27.
    #
    
    def typestring(self, token):
        return None

    def error(self, token):
        print "Syntax error at or near `%s' token" % token
        raise SystemExit

    def parse(self, tokens):
        tree = {}
        tokens.append(self._EOF)
        states = { 0: [ (self.startRule, 0, 0) ] }
        
        if self.ruleschanged:
            self.makeFIRST()

        for i in xrange(len(tokens)):
            states[i+1] = []

            if states[i] == []:
                break               
            self.buildState(tokens[i], states, i, tree)

        #_dump(tokens, states)

        if i < len(tokens)-1 or states[i+1] != [(self.startRule, 2, 0)]:
            del tokens[-1]
            self.error(tokens[i-1])
        rv = self.buildTree(tokens, tree, ((self.startRule, 2, 0), i+1))
        del tokens[-1]
        return rv

    def buildState(self, token, states, i, tree):
        needsCompletion = {}
        state = states[i]
        predicted = {}
        
        for item in state:
            rule, pos, parent = item
            lhs, rhs = rule

            #
            #  A -> a . (completer)
            #
            if pos == len(rhs):
                if len(rhs) == 0:
                    needsCompletion[lhs] = (item, i)

                for pitem in states[parent]:
                    if pitem is item:
                        break

                    prule, ppos, pparent = pitem
                    plhs, prhs = prule

                    if prhs[ppos:ppos+1] == (lhs,):
                        new = (prule,
                               ppos+1,
                               pparent)
                        if new not in state:
                            state.append(new)
                            tree[(new, i)] = [(item, i)]
                        else:
                            tree[(new, i)].append((item, i))
                continue

            nextSym = rhs[pos]

            #
            #  A -> a . B (predictor)
            #
            if nextSym in self.rules:
                #
                #  Work on completer step some more; for rules
                #  with empty RHS, the "parent state" is the
                #  current state we're adding Earley items to,
                #  so the Earley items the completer step needs
                #  may not all be present when it runs.
                #
                if nextSym in needsCompletion:
                    new = (rule, pos+1, parent)
                    olditem_i = needsCompletion[nextSym]
                    if new not in state:
                        state.append(new)
                        tree[(new, i)] = [olditem_i]
                    else:
                        tree[(new, i)].append(olditem_i)

                #
                #  Has this been predicted already?
                #
                if nextSym in predicted:
                    continue
                predicted[nextSym] = 1

                ttype = token is not self._EOF and \
                    self.typestring(token) or \
                    None
                if ttype is not None:
                    #
                    #  Even smarter predictor, when the
                    #  token's type is known.  The code is
                    #  grungy, but runs pretty fast.  Three
                    #  cases are looked for: rules with
                    #  empty RHS; first symbol on RHS is a
                    #  terminal; first symbol on RHS is a
                    #  nonterminal (and isn't nullable).
                    #
                    for prule in self.rules[nextSym]:
                        new = (prule, 0, i)
                        prhs = prule[1]
                        if len(prhs) == 0:
                            state.append(new)
                            continue
                        prhs0 = prhs[0]
                        if prhs0 not in self.rules:
                            if prhs0 != ttype:
                                continue
                            else:
                                state.append(new)
                                continue
                        first = self.first[prhs0]
                        if None not in first and \
                           ttype not in first:
                            continue
                        state.append(new)
                    continue

                for prule in self.rules[nextSym]:
                    #
                    #  Smarter predictor, as per Grune &
                    #  Jacobs' _Parsing Techniques_.  Not
                    #  as good as FIRST sets though.
                    #
                    prhs = prule[1]
                    if len(prhs) > 0 and \
                       prhs[0] not in self.rules and \
                       token != prhs[0]:
                        continue
                    state.append((prule, 0, i))

            #
            #  A -> a . c (scanner)
            #
            elif token == nextSym:
                #assert new not in states[i+1]
                states[i+1].append((rule, pos+1, parent))

    def buildTree(self, tokens, tree, root):
        stack = []
        self.buildTree_r(stack, tokens, -1, tree, root)
        return stack[0]

    def buildTree_r(self, stack, tokens, tokpos, tree, root):
        (rule, pos, parent), state = root
        
        while pos > 0:
            want = ((rule, pos, parent), state)
            if want not in tree:
                #
                #  Since pos > 0, it didn't come from closure,
                #  and if it isn't in tree[], then there must
                #  be a terminal symbol to the left of the dot.
                #  (It must be from a "scanner" step.)
                #
                pos = pos - 1
                state = state - 1
                stack.insert(0, tokens[tokpos])
                tokpos = tokpos - 1
            else:
                #
                #  There's a NT to the left of the dot.
                #  Follow the tree pointer recursively (>1
                #  tree pointers from it indicates ambiguity).
                #  Since the item must have come about from a
                #  "completer" step, the state where the item
                #  came from must be the parent state of the
                #  item the tree pointer points to.
                #
                children = tree[want]
                if len(children) > 1:
                    child = self.ambiguity(children)
                else:
                    child = children[0]
                
                tokpos = self.buildTree_r(stack,
                              tokens, tokpos,
                              tree, child)
                pos = pos - 1
                (crule, cpos, cparent), cstate = child
                state = cparent
                
        lhs, rhs = rule
        result = self.rule2func[rule](stack[:len(rhs)])
        stack[:len(rhs)] = [result]
        return tokpos

    def ambiguity(self, children):
        #
        #  XXX - problem here and in collectRules() if the same
        #    rule appears in >1 method.  But in that case the
        #    user probably gets what they deserve :-)  Also
        #    undefined results if rules causing the ambiguity
        #    appear in the same method.
        #
        sortlist = []
        name2index = {}
        for i in range(len(children)):
            ((rule, pos, parent), index) = children[i]
            lhs, rhs = rule
            name = self.rule2name[rule]
            sortlist.append((len(rhs), name))
            name2index[name] = i
        sortlist.sort()
        list = map(lambda (a,b): b, sortlist)
        return children[name2index[self.resolve(list)]]

    def resolve(self, list):
        #
        #  Resolve ambiguity in favor of the shortest RHS.
        #  Since we walk the tree from the top down, this
        #  should effectively resolve in favor of a "shift".
        #
        return list[0]

#
#  GenericASTBuilder automagically constructs a concrete/abstract syntax tree
#  for a given input.  The extra argument is a class (not an instance!)
#  which supports the "__setslice__" and "__len__" methods.
#
#  XXX - silently overrides any user code in methods.
#

class GenericASTBuilder(GenericParser):
    def __init__(self, AST, start):
        GenericParser.__init__(self, start)
        self.AST = AST

    def preprocess(self, rule, func):
        rebind = lambda lhs, self=self: \
                lambda args, lhs=lhs, self=self: \
                    self.buildASTNode(args, lhs)
        lhs, rhs = rule
        return rule, rebind(lhs)

    def buildASTNode(self, args, lhs):
        children = []
        for arg in args:
            if isinstance(arg, self.AST):
                children.append(arg)
            else:
                children.append(self.terminal(arg))
        return self.nonterminal(lhs, children)

    def terminal(self, token):  return token

    def nonterminal(self, type, args):
        rv = self.AST(type)
        rv[:len(args)] = args
        return rv

#
#  GenericASTTraversal is a Visitor pattern according to Design Patterns.  For
#  each node it attempts to invoke the method n_<node type>, falling
#  back onto the default() method if the n_* can't be found.  The preorder
#  traversal also looks for an exit hook named n_<node type>_exit (no default
#  routine is called if it's not found).  To prematurely halt traversal
#  of a subtree, call the prune() method -- this only makes sense for a
#  preorder traversal.  Node type is determined via the typestring() method.
#

class GenericASTTraversalPruningException:
    pass

class GenericASTTraversal:
    def __init__(self, ast):
        self.ast = ast

    def typestring(self, node):
        return node.type

    def prune(self):
        raise GenericASTTraversalPruningException

    def preorder(self, node=None):
        if node is None:
            node = self.ast

        try:
            name = 'n_' + self.typestring(node)
            if hasattr(self, name):
                func = getattr(self, name)
                func(node)
            else:
                self.default(node)
        except GenericASTTraversalPruningException:
            return

        for kid in node:
            self.preorder(kid)

        name = name + '_exit'
        if hasattr(self, name):
            func = getattr(self, name)
            func(node)

    def postorder(self, node=None):
        if node is None:
            node = self.ast

        for kid in node:
            self.postorder(kid)

        name = 'n_' + self.typestring(node)
        if hasattr(self, name):
            func = getattr(self, name)
            func(node)
        else:
            self.default(node)


    def default(self, node):
        pass

#
#  GenericASTMatcher.  AST nodes must have "__getitem__" and "__cmp__"
#  implemented.
#
#  XXX - makes assumptions about how GenericParser walks the parse tree.
#

class GenericASTMatcher(GenericParser):
    def __init__(self, start, ast):
        GenericParser.__init__(self, start)
        self.ast = ast

    def preprocess(self, rule, func):
        rebind = lambda func, self=self: \
                lambda args, func=func, self=self: \
                    self.foundMatch(args, func)
        lhs, rhs = rule
        rhslist = list(rhs)
        rhslist.reverse()

        return (lhs, tuple(rhslist)), rebind(func)

    def foundMatch(self, args, func):
        func(args[-1])
        return args[-1]

    def match_r(self, node):
        self.input.insert(0, node)
        children = 0

        for child in node:
            if children == 0:
                self.input.insert(0, '(')
            children = children + 1
            self.match_r(child)

        if children > 0:
            self.input.insert(0, ')')

    def match(self, ast=None):
        if ast is None:
            ast = self.ast
        self.input = []

        self.match_r(ast)
        self.parse(self.input)

    def resolve(self, list):
        #
        #  Resolve ambiguity in favor of the longest RHS.
        #
        return list[-1]

def _dump(tokens, states):
    for i in range(len(states)):
        print 'state', i
        for (lhs, rhs), pos, parent in states[i]:
            print '\t', lhs, '::=',
            print ' '.join(rhs[:pos]),
            print '.',
            print ' '.join(rhs[pos:]),
            print ',', parent
        if i < len(tokens):
            print
            print 'token', str(tokens[i])
            print

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