Question

我想解析化学元素数据库的查询。

数据库存储在xml文件中。解析该文件会生成嵌套字典，该字典存储在从collections.OrderedDict继承的单例对象中。

要求元素将为我提供其相应属性的有序字典（即ELEMENTS ['C'] - ＆gt; {'name'：'carbon'，'neutron'：0，'proton'：6，...}）。

相反，要求一个属性将给我一个有序的字典，其中包含所有元素的值（即ELEMENTS ['proton'] - ＆gt; {'H'：1，'他'：2} ... ）。

典型的查询可能是：

mass > 10 or (nucleon < 20 and atomic_radius < 5)

其中每个“子查询”（即质量> 10）将返回与其匹配的元素集。

然后，查询将被转换并在内部转换为一个字符串，该字符串将进一步评估以生成与其匹配的元素的一组索引。在该上下文中，运算符和/或不是布尔运算符，而是作用于python集的集合运算符。

我最近发了一篇建立此类查询的帖子。感谢我得到的有用答案，我认为我做了或多或少的工作（我希望以一种不错的方式！）但我仍然有一些与pyparsing有关的问题。

这是我的代码：

import numpy

from pyparsing import *

# This import a singleton object storing the datase dictionary as
# described earlier
from ElementsDatabase import ELEMENTS

and_operator = oneOf(['and','&'], caseless=True) 
or_operator  = oneOf(['or' ,'|'], caseless=True) 

# ELEMENTS.properties is a property getter that returns the list of 
# registered properties in the database
props = oneOf(ELEMENTS.properties, caseless=True)

# A property keyword can be quoted or not.
props = Suppress('"') + props + Suppress('"') | props
# When parsed, it must be replaced by the following expression that 
# will be eval later.
props.setParseAction(lambda t : "numpy.array(ELEMENTS['%s'].values())" % t[0].lower())

quote = QuotedString('"')
integer = Regex(r'[+-]?\d+').setParseAction(lambda t:int(t[0]))
float_  = Regex(r'[+-]?(\d+(\.\d*)?)?([eE][+-]?\d+)?').setParseAction(lambda t:float(t[0]))

comparison_operator = oneOf(['==','!=','>','>=','<', '<='])
comparison_expr = props + comparison_operator + (quote | float_ | integer)
comparison_expr.setParseAction(lambda t : "set(numpy.where(%s)%s%s)" % tuple(t))

grammar = Combine(operatorPrecedence(comparison_expr, [(and_operator, 2, opAssoc.LEFT) (or_operator, 2, opAssoc.LEFT)]))

# A test query
res = grammar.parseString('"mass     "  >  30 or (nucleon == 1)',parseAll=True)

print eval(' '.join(res._asStringList()))

我的问题如下：

1 using 'transformString' instead of 'parseString' never triggers any 
  exception even when the string to be parsed does not match the grammar. 
  However, it is exactly the functionnality I need. Is there is a way to do so ?

2 I would like to reintroduce white spaces between my tokens in order 
that my eval does not fail. The only way I found to do so it the one 
implemented above. Would you see a better way using pyparsing ?

对于这篇长篇文章感到抱歉，但我想更详细地介绍它的背景。顺便说一句，如果你发现这种方法不好，请不要犹豫告诉我！

非常感谢你的帮助。

埃里克

Answer 1

不要担心我的担心，我找到了解决方法。我使用了pyparsing附带的SimpleBool.py示例（感谢Paul的提示）。

基本上，我使用了以下方法：

1 for each subquery (i.e. mass > 10), using the setParseAction method, 
I joined a function that returns the set of eleements that matched 
the subquery

2 then, I joined the following functions for each logical operator (and, 
or and not):

def not_operator(token):

    _, s = token[0]

    # ELEMENTS is the singleton described in my original post
    return set(ELEMENTS.keys()).difference(s)

def and_operator(token):

    s1, _, s2 = token[0]

    return (s1 and s2)

def or_operator(token):

    s1, _, s2 = token[0]

    return (s1 or s2)

# Thanks for Paul for the hint.
grammar = operatorPrecedence(comparison_expr,
          [(not_token, 1,opAssoc.RIGHT,not_operator),
          (and_token, 2, opAssoc.LEFT,and_operator),
          (or_token, 2, opAssoc.LEFT,or_operator)])

Please not that these operators acts upon python sets rather than 
on booleans.

这就是工作。

我希望这种方法可以帮助你们。

Eric

用于查询化学元素数据库的pyparsing

1 个答案: