Question

我开发了一个必须在输出中插入新标记的pyparsing语法。此令牌不是来自原始输入。

例：

输入：

'/* foo bar*/'

输出继电器：

['comment', '/* foo bar*/']

如果这些元素不在原始表达式中，如何将元素添加到解析器输出中？

Answer 1

阅读pyparsing's API我找到了一个名为 replaceWith 的暗示名称的函数。使用此函数和 addParseAction 我能够解决问题。

以下代码是问题的解决方案：

from pyparsing import *

crazyVariable = Empty().addParseAction(replaceWith('comment')) + cStyleComment

print(crazyVariable.parseString('/* foo bar*/' ))

输出：

['comment', '/* foo bar*/']

Answer 2

实现相同结果的另一种方法，也许是具有更强表现力的方法，是使用命名表达式。例如：

from pyparsing import *

grammar = cStyleComment("comment")
s = '/* foo bar*/' 

sol = grammar.parseString(s)
print sol.asDict()

>>> {'comment': '/* foo bar*/'}

您会注意到您没有按照预期的列表，但这样可以让您在结果变得更复杂时直接访问结果。让我们看看实际行动：

code    = Word(alphanums+'(){},.<>"; ') 
grammar = OneOrMore(code("code") | cStyleComment("comment"))
s = 'cout << "foobar"; /* foo bar*/' 

sol = grammar.parseString(s)
print "code:", sol["code"]
print "comment", sol["comment"]

>>> code: cout << "foobar"; 
>>> comment: /* foo bar*/

Answer 3

这个替代解决方案并不完全是标题中问题的答案，而是问题旨在解决的更普遍问题的答案：

如何使用从类实例化的节点对象构建语法树：

# -*- coding: utf-8 -*-

from pyparsing import *



def uncommentCStyleComment(t):  ''' remove /* and */ from a comment '''; return t[0][2:-2]


''' 
classes which replaces functions as arguments in setParseAction or addParseAction 
each class will be used to build a node in a syntax tree
t argument on constructor is the list of child nodes of the node 
'''




class Foo(object):
    def __init__(self,t):   self.value = t[0]   # t = ['foo']

    def __str__(self):      return self.value   # return 'foo'

class Bar(object):
    members = []                                    # list of foos and comments

    def __init__(self,t):   self.members.extend(t)  # t = list of foos and comments

    def __str__(self):
        _str = 'Bar:\n'      
        for member in self.members: _str = _str + '\t' + str(member) + '\n'             
        return _str

class Comment(object):
    def __init__(self,t):   self.value = t[0];                      # t = ['/* Some comment */']

    def __str__(self):      return '/*' + str(self.value) + '*/'    # return '/* Some comment */'



# return an object of type Foo instead a token
foo     = Combine('foo')                    .setParseAction(Foo)
# uncomment and return an object of type Comment instead a token
comment = cStyleComment                     .setParseAction(uncommentCStyleComment, Comment) 
# return an object of type Bar instead a token
bar     = OneOrMore(comment | foo)('ast')   .setParseAction(Bar)

# parse the input string
tokens = bar.parseString('foo\n/* data bar*/\nfoo\nfoo' )

# print the object named ast in the parser output
print( tokens['ast'] )

这是一种非常优雅的构建输出方式，无需后期处理。

Pyparsing：如何将新元素插入ParseResult

3 个答案: