An infix evaluator implementing the shunting yard algorithm

Infix.py

import re
from operator import *
class Math(Exception):
    pass
class InfixException(Math):
    pass
re_float = re.compile(r'^(\d+\.\d*)|(\d*\.\d+)$')
re_int = re.compile(r'^\d+$')
class Infix:
    def __init__(self):
        self.op_map = {
            '(':(15,None,None,None),
            '~':(14,'R',inv,1),
            '!':(14,'R',lambda x: 1 if x == 0 else 0,1),
            '*':(13,'L',mul,2),
            '/':(13,'L',div,2),
            '%':(13,'L',mod,2),
            '+':(12,'L',add,2),
            '-':(12,'L',sub,2),
            '&':(8,'L',and_,2),
            '^':(7,'L',xor,2),
            '|':(6,'L',or_,2),
            ')':(0,None,None,None)
            }
        self.numeric = "1234567890."
        self.operators = "+-*/%^|!~()"
    def bufout(self):
        if self.buff:
            if re_float.match(self.buff):
                self.out.append(float(self.buff))
            elif re_int.match(self.buff):
                self.out.append(int(self.buff))
            else:
                raise InfixException("'%s' not of type 'int' or 'float'" % self.buff)
            self.buff = ""
    def get(self,key,token):
        keys = ['prec','assoc','op','args']
        return self.op_map[token][keys.index(key)]
    def apply(self,token):
        op, args = self.get('op',token), self.get('args',token)
        if len(self.out) >= args:
            self.out.append(op(*[self.out.pop() for i in range(args)][::-1]))
        else:
            raise InfixException("Not enough arguments to apply operation '%s'" % token)
    def eval(self,expr):
        self.out, self.stack = [], []
        self.buff = ""

        for token in expr:
            if token in self.numeric:
                self.buff += token
            elif token in self.operators[:-4]:
                self.bufout()
                p = self.get('prec',token)
                while self.stack and self.get('prec',self.stack[-1]) >= p and self.stack[-1] != '(':
                    self.apply(self.stack.pop())
                self.stack.append(token)
            elif token in self.operators[-4:-2]:
                self.bufout()
                p = self.get('prec',token)
                while self.stack and self.get('prec',self.stack[-1]) > p and self.stack[-1] != '(':
                    self.apply(self.stack.pop())
                self.stack.append(token)
            elif token in self.operators[-2]:
                self.bufout()
                self.stack.append(token)
            elif token in self.operators[-1]:
                self.bufout()
                while self.stack and self.stack[-1] != '(':
                    token = self.stack.pop()
                    self.apply(token)
                if self.stack and self.stack[-1] == '(':
                    self.stack.pop()
        self.bufout()
        while self.stack:
            token = self.stack.pop()
            if token in self.operators[:-2]:
                self.apply(token)
        return self.out[0] if len(self.out) == 1 else self.out