pyparsing问题

from pyparsing import *
integer = Word(nums)
op = Word(\"+-*/^\", max=1)
space = Word(\" \")
expr = Word(nums)+space+Word(nums)+space+op
parsed = expr.parseString(\"3 4 *\")
print parsed

Traceback (most recent call last):
  File \"star_parse.py\", line 6, in <module>
    parsed = expr.parseString(\"3 4 *\")
  File \"/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/site-packages/pyparsing-1.5.5-py2.6.egg/pyparsing.py\", line 1100, in parseString
    raise exc
pyparsing.ParseException: Expected W:( ) (at char 2), (line:1, col:3)

oneOf

from pyparsing import *
integer = Word(nums)
op = oneOf(\'* + - / ^\')
expr = integer + integer + op
parsed = expr.parseString(\"3 4 *\")
print parsed

expr = integer + integer + op