python - 解析问题

Question

现在我刚刚开始使用pyparsing来解析简单的后缀表达式。目前，我做到了这一点：

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

但是当我运行它时，它会打印：

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)

我究竟做错了什么？

Answer 1

默认情况下处理空白。还有方便的oneOf：

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

Answer 2

pyparser 会忽略空格。您可以使用 White 类显式测试空格。

但是，您可能正在寻找的表达式是：

expr = integer + integer + op

http://packages.python.org/pyparsing/pyparsing.pyparsing.White-class.html