Pyparsing setParseAction函数没有参数

Question

我正在尝试解析一个简单的key = value查询语言.我实际上是用一个巨大的怪物解析器完成它,然后我再次通过来清理解析树.我想要做的是从下往上,其中包括像使用套为划清解析(KEY,VAL)对,这样对冗余消除等,虽然我之前的工作,我不觉得就像我完全理解为什么pyparsing按照它的方式行事,所以我做了大量的工作等等,有点像对抗谷物.

目前,这是我的"简化"解析器的开头:

from pyparsing import *   

bool_act = lambda t: bool(t[0])
int_act  = lambda t: int(t[0])

def keyval_act(instring, loc, tokens):
    return set([(tokens.k, tokens.v)])

def keyin_act(instring, loc, tokens):
    return set([(tokens.k, set(tokens.vs))])

string = (
      Word(alphas + '_', alphanums + '_')
    | quotedString.setParseAction( removeQuotes )
    )
boolean = (
      CaselessLiteral('true')
    | CaselessLiteral('false')
    )
integer = Word(nums).setParseAction( int_act )
value = (
      boolean.setParseAction(bool_act)
    | integer
    | string
    )
keyval = (string('k') + Suppress('=') + value('v')
          ).setParseAction(keyval_act)
keyin = (
    string('k') + Suppress(CaselessLiteral('in')) +
    nestedExpr('{','}', content = delimitedList(value)('vs'))
    ).setParseAction(keyin_act)

grammar = keyin + stringEnd | keyval + stringEnd

目前,"语法"非终结符只是一个存根,我最终会为键添加可嵌套的连词和析取,以便可以解析这样的搜索:

a = 1, b = 2 , c in {1,2,3} | d = 4, ( e = 5 | e = 2, (f = 3, f = 4))

但就目前而言,我无法理解pyparsing如何调用我的setParseAction函数.我知道在传递了多少个参数方面有一些魔力,但是我得到一个错误,其中没有任何参数传递给函数.所以目前,如果我这样做:

grammar.parseString('hi in {1,2,3}')

我收到此错误:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python2.6/site-packages/pyparsing.py", line 1021, in parseString
    loc, tokens = self._parse( instring, 0 )
  File "/usr/lib/python2.6/site-packages/pyparsing.py", line 894, in _parseNoCache
    loc,tokens = self.parseImpl( instring, preloc, doActions )
  File "/usr/lib/python2.6/site-packages/pyparsing.py", line 2478, in parseImpl
    ret = e._parse( instring, loc, doActions )
  File "/usr/lib/python2.6/site-packages/pyparsing.py", line 894, in _parseNoCache
    loc,tokens = self.parseImpl( instring, preloc, doActions )
  File "/usr/lib/python2.6/site-packages/pyparsing.py", line 2351, in parseImpl
    loc, resultlist = self.exprs[0]._parse( instring, loc, doActions, callPreParse=False )
  File "/usr/lib/python2.6/site-packages/pyparsing.py", line 921, in _parseNoCache
    tokens = fn( instring, tokensStart, retTokens )
  File "/usr/lib/python2.6/site-packages/pyparsing.py", line 675, in wrapper
    return func(*args[limit[0]:])
TypeError: keyin_act() takes exactly 3 arguments (0 given)

从traceback中可以看出,我使用的是python2.6,而pyparsing是1.5.6

谁能让我深入了解为什么函数没有得到正确数量的参数？

Answer 1

嗯,最新版本setParseAction确实做了一些额外的魔术,但遗憾的是牺牲了一些开发的简单性.setParseAction中的参数检测逻辑现在依赖于在解析操作中引发异常,直到使用正确数量的参数调用它,从3开始并向下运行到0,之后它只是放弃并引发异常你锯.

除了在这种情况下,来自解析操作的异常不是由于参数列表不匹配,而是代码中的实际错误.要获得更好的视图,请在您的解析操作中插入一个通用的try-except:

def keyin_act(instring, loc, tokens): 
    try:
        return set([(tokens.k, set(tokens.vs[0]))]) 
    except Exception as e:
        print e

你得到:

unhashable type: 'set'

事实上,您创建返回集的列表的第二个元素本身就是一个集合,一个可变容器,因此无法包含在集合中.如果你改为使用冷冻集代替,那么你会得到:

[set([('hi', frozenset([]))])]

为什么冻结空？我建议您将结果名称'vs'的位置更改为:

nestedExpr('{','}', content = delimitedList(value))('vs') 

现在解析'hi in {1,2,3}'返回的解析结果是:

[set([('hi', frozenset([([1, 2, 3], {})]))])]

这是一个混乱,如果我们将此行放在您的解析操作的顶部,您将看到不同的命名结果实际包含的内容:

print tokens.dump()

我们得到:

['hi', [1, 2, 3]]
- k: hi
- vs: [[1, 2, 3]]

因此'vs'实际指向包含列表的列表.所以我们可能想要构建我们的集合tokens.vs[0],而不是tokens.vs.现在我们的解析结果如下:

[set([('hi', frozenset([1, 2, 3]))])]

关于语法的一些其他提示:

• 而不是CaselessLiteral,尝试使用CaselessKeyword.关键字是语法关键词的更好选择,因为它们固有地避免将"内部"的前导"输入"误认为语法中的关键词"in".

• 不确定从解析操作返回集合的方向 - 对于键值对,元组可能会更好,因为它将保留令牌的顺序.在程序的解析后阶段构建您的键和值集.

• 对于其他语法调试工具,请查看setDebug和traceParseAction装饰器.

Answer 2

保罗已经解释了根本问题是什么:TypeError你的解析行为所引发的混淆了pyparsing的自动化方式来计算你的解析动作所期望的参数数量.

这是我用来避免这种混淆的东西:一个装饰器,TypeError如果用较少的参数再次调用该函数,则重新引发由装饰函数抛出的任何东西:

import functools
import inspect
import sys

def parse_action(f):
    """
    Decorator for pyparsing parse actions to ease debugging.

    pyparsing uses trial & error to deduce the number of arguments a parse
    action accepts. Unfortunately any ``TypeError`` raised by a parse action
    confuses that mechanism.

    This decorator replaces the trial & error mechanism with one based on
    reflection. If the decorated function itself raises a ``TypeError`` then
    that exception is re-raised if the wrapper is called with less arguments
    than required. This makes sure that the actual ``TypeError`` bubbles up
    from the call to the parse action (instead of the one caused by pyparsing's
    trial & error).
    """
    num_args = len(inspect.getargspec(f).args)
    if num_args > 3:
        raise ValueError('Input function must take at most 3 parameters.')

    @functools.wraps(f)
    def action(*args):
        if len(args) < num_args:
            if action.exc_info:
                raise action.exc_info[0], action.exc_info[1], action.exc_info[2]
        action.exc_info = None
        try:
            return f(*args[:-(num_args + 1):-1])
        except TypeError as e:
            action.exc_info = sys.exc_info()
            raise

    action.exc_info = None
    return action

以下是如何使用它:

from pyparsing import Literal

@parse_action
def my_parse_action(tokens):
    raise TypeError('Ooops')

x = Literal('x').setParseAction(my_parse_action)
x.parseString('x')

这给你:

Traceback (most recent call last):
  File "test.py", line 49, in <module>
    x.parseString('x')
  File "/usr/local/lib/python2.7/dist-packages/pyparsing-2.0.2-py2.7.egg/pyparsing.py", line 1101, in parseString
    loc, tokens = self._parse( instring, 0 )
  File "/usr/local/lib/python2.7/dist-packages/pyparsing-2.0.2-py2.7.egg/pyparsing.py", line 1001, in _parseNoCache
    tokens = fn( instring, tokensStart, retTokens )
  File "/usr/local/lib/python2.7/dist-packages/pyparsing-2.0.2-py2.7.egg/pyparsing.py", line 765, in wrapper
    ret = func(*args[limit[0]:])
  File "test.py", line 33, in action
    return f(*args[:num_args])
  File "test.py", line 46, in my_parse_action
    raise TypeError('Ooops')
TypeError: Ooops

将此与没有@parse_action装饰的回溯进行比较:

Traceback (most recent call last):
  File "test.py", line 49, in <module>
    x.parseString('x')
  File "/usr/local/lib/python2.7/dist-packages/pyparsing-2.0.2-py2.7.egg/pyparsing.py", line 1101, in parseString
    loc, tokens = self._parse( instring, 0 )
  File "/usr/local/lib/python2.7/dist-packages/pyparsing-2.0.2-py2.7.egg/pyparsing.py", line 1001, in _parseNoCache
    tokens = fn( instring, tokensStart, retTokens )
  File "/usr/local/lib/python2.7/dist-packages/pyparsing-2.0.2-py2.7.egg/pyparsing.py", line 765, in wrapper
    ret = func(*args[limit[0]:])
TypeError: my_parse_action() takes exactly 1 argument (0 given)