区分pyparsing中的匹配项

Question

我想用 pyparsing 解析一些单词和一些数字。简单吧。

from pyparsing import *

A = Word(nums).setResultsName('A')
B = Word(alphas).setResultsName('B')
expr = OneOrMore(A | B)

result = expr.parseString("123 abc 456 7 d")
print result

上面的代码打印 ['123', 'abc', '456', '7', 'd']。所以一切正常。现在我想对这些解析后的值做一些工作。对于此任务，我需要知道它们是否匹配 A 或 B。有没有办法区分这两者。

经过一番研究，我唯一发现的是 ParseResults class 的 items 方法。但它只有returns[('A', '7'), ('B', 'd')]，只有最后两个匹配项。

我的计划/目标如下：

for elem in result:
    if elem.is_of_type('A'):
        # do stuff
    elif elem.is_of_type('B'):
        # do something else

如何区分 A 和 B？

Answer 1

我不完全确定为什么，但在您的 .setResultsName() 调用中，您需要指定 listAllMatches=True（默认为 False）。完成后，您可以遍历 result 并通过检查 result.

的适当子项中的成员资格来检查每个标记是否与给定表达式匹配

from pyparsing import *

#                                    ↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓
A = Word(nums  ).setResultsName('A', listAllMatches=True)
B = Word(alphas).setResultsName('B', listAllMatches=True)
expr = OneOrMore(A | B)

result = expr.parseString("123 abc 456 7 d")

for elem in result:
    if elem in list(result['A']):
        print(elem, 'is in A')
    elif elem in list(result['B']):
        print(elem, 'is in B')

这会打印：

123 is in A
abc is in B
456 is in A
7 is in A
d is in B

这有点乱七八糟，我不确定这样做是否是规范正确的方法，但它似乎有效。

Answer 2

我自己找到了解决办法。 ParseResults class 有一个 getName() 方法。但是简单地遍历 result 并打印 getName() 会抛出错误，因为 ParseResults 对象会产生字符串。一种解决方案是将 A 和 B 放入 Groups。不确定这是否是最好的方法，但效果很好。

from pyparsing import *

A = Group(Word(nums)).setResultsName('A', listAllMatches=True)
B = Group(Word(alphas)).setResultsName('B', listAllMatches=True)
expr = OneOrMore(A | B)

result = expr.parseString("123 abc 456 7 d")

for i in  result:
    if i.getName() == 'A':
       print i[0], 'is a number'
    elif i.getName() == 'B':
       print i[0], 'is a string'

Answer 3

getName() 做得不错。您还可以使用标记显式修饰返回的标记，指示进行了哪个匹配：

def makeDecoratingParseAction(marker):
    def parse_action_impl(s,l,t):
        return (marker, t[0])
    return parse_action_impl

A = Word(nums).setParseAction(makeDecoratingParseAction("A"))
B = Word(alphas).setParseAction(makeDecoratingParseAction("B"))
expr = OneOrMore(A | B)

result = expr.parseString("123 abc 456 7 d")
print result.asList()

给出：

[('A', '123'), ('B', 'abc'), ('A', '456'), ('A', '7'), ('B', 'd')]

现在您可以迭代返回的元组，每个元组都标有适当的标记。

您可以更进一步，使用 class 来捕获类型和类型特定的 post-解析逻辑，然后将 class 作为表达式的解析动作。这将在返回的 ParseResults 中创建 classes 的实例，然后您可以使用某种 exec 或 doIt 方法直接执行：

class ResultsHandler(object):
    """Define base class to initialize location and tokens.
       Call subclass-specific post_init() if one is defined."""
    def __init__(self, s,locn,tokens):
        self.locn = locn
        self.tokens = tokens
        if hasattr(self, "post_init"):
            self.post_init()

class AHandler(ResultsHandler):
    """Handler for A expressions, which contain a numeric string."""
    def post_init(self):
        self.int_value = int(self.tokens[0])
        self.odd_even = ("EVEN","ODD")[self.int_value % 2]
    def doIt(self):
        print "An A-Type was found at %d with value %d, which is an %s number" % (
                self.locn, self.int_value, self.odd_even)

class BHandler(ResultsHandler):
    """Handler for B expressions, which contain an alphabetic string."""
    def post_init(self):
        self.string = self.tokens[0]
        self.vowels_count = sum(self.string.lower().count(c) for c in "aeiou")
    def doIt(self):
        print "A B-Type was found at %d with value %s, and contains %d vowels" % (
                self.locn, self.string, self.vowels_count)


# pass expression-specific handler classes as parse actions
A = Word(nums).setParseAction(AHandler)
B = Word(alphas).setParseAction(BHandler)
expr = OneOrMore(A | B)

# parse string and run handlers
result = expr.parseString("123 abc 456 7 d")
for handler in result:
    handler.doIt()

打印：

An A-Type was found at 0 with value 123, which is an ODD number
A B-Type was found at 4 with value abc, and contains 1 vowels
An A-Type was found at 8 with value 456, which is an EVEN number
An A-Type was found at 12 with value 7, which is an ODD number
A B-Type was found at 14 with value d, and contains 0 vowels

区分pyparsing中的匹配项

Distinguish matches in pyparsing

python

python-2.7

parsing

pyparsing