jw-python/tools/python/jwutils/algo/ShuntingYard.py

from collections import namedtuple
import re

Operator = namedtuple("Operator", [ "func", "nargs" , "prec" ])

class Stack:

    def __init__(self, itemlist=[]):
        self.items = itemlist

    def isEmpty(self):
        if self.items == []:
            return True
        return False

    def peek(self):
        return self.items[-1:][0]

    def pop(self):
        return self.items.pop()

    def push(self, item):
        self.items.append(item)
        return 0

class ShuntingYard(object): # export

    def __init__(self, operators):
        self.__ops = {}
        for k, v in operators.iteritems():
            self.add_operator(k, v.func, v.nargs, v.prec)

    def tokenize(self, spec):

        regex = ""
        for k in self.__ops.keys():
            regex = regex + "|" + re.escape(k)

        regex = regex[1:]

        scanner = re.Scanner([
          (regex,       lambda scanner,token:("kw", token)),
          (r"\w+",      lambda scanner,token:("arg", token)),
          (r"\s+", None), # None == skip token.
        ])

        tokens, remainder = scanner.scan(spec)
        if len(remainder)>0:
            raise Expression("Failed to tokenize " + spec + ", remaining bit is ", remainder)

        print tokens
        r = []
        for e in tokens:
            r.append(e[1])

        return r

    def add_operator(self, name, func, nargs, precedence):
        self.__ops[name] = Operator(func, nargs, precedence)

    def infix_to_postfix(self, infix):

        s = Stack()
        r = []
        tokens = self.tokenize(infix)

        for token in tokens:

            print "Checking token ", token

            if token not in self.__ops.keys():
                r.append(token)
                continue

            if token == '(':
                s.push(token)
                continue

            if token == ')':
                topToken = s.pop()
                while topToken != '(':
                    r.append(topToken)
                    topToken = s.pop()
                continue

            while (not s.isEmpty()) and (self.__ops[s.peek()].prec >= self.__ops[token].prec):
                #print token
                r.append(s.pop())
                #print r

            s.push(token)
            print (s.peek())

        while not s.isEmpty():
            opToken = s.pop()
            r.append(opToken)
            #print r

        return r
        #return " ".join(r)

    def eval_postfix(self, postfixexpr):

        vals = Stack()

        for token in postfixexpr:

            if token not in self.__ops.keys():
                vals.push(token)
                continue

            op = self.__ops[token]
            args = []
            #print "Adding %d arguments" % (op.nargs)
            for i in range(0, op.nargs):
                #print "Adding argument %d" % (i)
                args.append(vals.pop())
            val = op.func(*reversed(args))
            print "%s(%s) = %s" % (token, ', '.join(reversed(args)), val)
            vals.push(val)

        return vals.pop()

    def eval(self, infix):
        postfix = self.infix_to_postfix(infix)
        print infix, "-->", postfix
        return self.eval_postfix(postfix)

if __name__ == '__main__':

    # ------------- testbed calculator

    from string import atof

    class Calculator(ShuntingYard):

        def tokenize(self, string):
            return string.split()

        def f_mult(self, a, b):
            return str(atof(a) * atof(b));

        def f_div(self, a, b):
            return str(atof(a) / atof(b));

        def f_add(self, a, b):
            return str(atof(a) + atof(b));

        def f_sub(self, a, b):
            return str(atof(a) - atof(b));

        def __init__(self):
            Op = Operator
            operators = {
                '/': Op(self.f_div,  2, 3),
                '*': Op(self.f_mult, 2, 3),
                '+': Op(self.f_add,  2, 2),
                '-': Op(self.f_sub,  2, 2),
                '(': Op(None,        2, 1),
                ')': Op(None,        2, 1)
            }
            super(Calculator, self).__init__(operators)

    print Calculator().eval("( 2 * 3 + 4 * 5 ) / ( 5 - 3 )")

    # ------------- testbed match object

    Object = namedtuple("Object", [ "Name", "Label" ])

    class Matcher(ShuntingYard):

        def f_is_name(self, a):
            if obj.Name == a:
                return "True"
            return "False"

        def f_matches_label(self, a):
            if re.match(a, obj.Label):
                return "True"
            return "False"

        def f_is_not(self, a):
            if a == "True":
                return "False"
            return "False"

        def f_and(self, a_, b_):
            a = a_ == "True"
            b = b_ == "True"
            if a and b:
                return "True"
            return "False"

        def __init__(self, obj):
            Op = Operator
            operators = {
                '(':       Op(None,                  2, 1),
                ')':       Op(None,                  2, 1),
                'name=':   Op(self.f_is_name,        1, 3),
                'and':     Op(self.f_and,            2, 3),
                'label~=': Op(self.f_matches_label,  1, 3),
                'False':   Op(None,                  0, 3),
                'True':    Op(None,                  0, 3),
                'not':     Op(self.f_is_not,         1, 3),
            }
            super(Matcher, self).__init__(operators)

    obj = Object("hans", "wurst")

    r = Matcher(obj).eval("name=hans and (not label~=worst)")
    print "Result =", r