xml DTD 文件的解析器答案

【问题标题】：Parser for xml DTD filexml DTD 文件的解析器
【发布时间】：2014-03-31 10:02:34
【问题描述】：

我在实现解析器方面非常新，我正在尝试解析 xml DTD 文件以为其生成上下文无关语法。我尝试了 pyparsing 和 yacc，但仍然可以得到任何结果。因此，如果有人可以为我提供一些技巧或示例代码来编写这样的解析器，我将不胜感激。以下是一个示例 DTD 文件：

<!DOCTYPE PcSpecs [
<!ELEMENT PCS (PC*)>
<!ELEMENT PC (MODEL, PRICE, PROCESSOR, RAM, DISK+)>
<!ELEMENT MODEL (\#PCDATA)>
<!ELEMENT PRICE (\#PCDATA)>
<!ELEMENT PROCESSOR (MANF, MODEL, SPEED)>
<!ELEMENT MANF (\#PCDATA)>
<!ELEMENT MODEL (\#PCDATA)>
<!ELEMENT SPEED (\#PCDATA)>
<!ELEMENT RAM (\#PCDATA)>
<!ELEMENT DISK (HARDDISK | CD | DVD)>
<!ELEMENT HARDDISK (MANF, MODEL, SIZE)>
<!ELEMENT SIZE (\#PCDATA)>
<!ELEMENT CD (SPEED)>
<!ELEMENT DVD (SPEED)>
]>

提前致谢。

【问题讨论】：

标签： python xml-parsing yacc lexer pyparsing

【解决方案1】：

这是一个开始，它会将数据解析为 ParseResults 数据结构，然后您可以遍历并为定义的文档类型创建解析器：

from pyparsing import *

LT,GT,EXCLAM,LBRACK,RBRACK,LPAR,RPAR = map(Suppress,"<>![]()")
DOCTYPE = Keyword("DOCTYPE").suppress()
ELEMENT = Keyword("ELEMENT").suppress()
ident = Word(alphas, alphanums+"_")
elementRef = Group(ident("name") + Optional(oneOf("* +")("rep")))
elementExpr = infixNotation(elementRef,
    [
    (',', 2, opAssoc.LEFT),
    ('|', 2, opAssoc.LEFT),
    ])
PCDATA = Literal(r"\#PCDATA")
elementDefn = Group(LT+EXCLAM + ELEMENT + ident("name") + 
                  LPAR + (elementExpr | PCDATA("PCDATA"))("contents") + RPAR + GT)
doctypeDefn = LT+EXCLAM + DOCTYPE + ident("name") + 
                    LBRACK + ZeroOrMore(elementDefn)("elements") + RBRACK + GT

我开始只对每个 ELEMENT 定义中的元素列表使用 delimitedList，但后来我注意到 ',' 和 '|'实际上是运算符，而不仅仅是分隔符，甚至可以混合使用，如 "A,B,C|D,E"。所以我使用了 pyparsing 的 infixNotation 助手来允许这些类型的定义。

使用您的输入样本，我可以解析并显示结果：

doctype = doctypeDefn.parseString(sample)
print doctype.dump()
for elem in doctype.elements:
    print elem.dump()

给予：

['PcSpecs', ['PCS', ['PC', '*']], ['PC', [['MODEL'], ...
- elements: [['PCS', ['PC', '*']], ['PC', [['MODEL'], ...
- name: PcSpecs
['PCS', ['PC', '*']]
- contents: ['PC', '*']
  - name: PC
  - rep: *
- name: PCS
['PC', [['MODEL'], ',', ['PRICE'], ',', ['PROCESSOR'], ',', ['RAM'], ',', ['DISK', '+']]]
- contents: [['MODEL'], ',', ['PRICE'], ',', ['PROCESSOR'], ',', ['RAM'], ',', ['DISK', '+']]
- name: PC
['MODEL', '\\#PCDATA']
- PCDATA: \#PCDATA
- contents: \#PCDATA
- name: MODEL
['PRICE', '\\#PCDATA']
- PCDATA: \#PCDATA
- contents: \#PCDATA
- name: PRICE
['PROCESSOR', [['MANF'], ',', ['MODEL'], ',', ['SPEED']]]
- contents: [['MANF'], ',', ['MODEL'], ',', ['SPEED']]
- name: PROCESSOR
['MANF', '\\#PCDATA']
- PCDATA: \#PCDATA
- contents: \#PCDATA
- name: MANF
['MODEL', '\\#PCDATA']
- PCDATA: \#PCDATA
- contents: \#PCDATA
- name: MODEL
['SPEED', '\\#PCDATA']
- PCDATA: \#PCDATA
- contents: \#PCDATA
- name: SPEED
['RAM', '\\#PCDATA']
- PCDATA: \#PCDATA
- contents: \#PCDATA
- name: RAM
['DISK', [['HARDDISK'], '|', ['CD'], '|', ['DVD']]]
- contents: [['HARDDISK'], '|', ['CD'], '|', ['DVD']]
- name: DISK
['HARDDISK', [['MANF'], ',', ['MODEL'], ',', ['SIZE']]]
- contents: [['MANF'], ',', ['MODEL'], ',', ['SIZE']]
- name: HARDDISK
['SIZE', '\\#PCDATA']
- PCDATA: \#PCDATA
- contents: \#PCDATA
- name: SIZE
['CD', ['SPEED']]
- contents: ['SPEED']
  - name: SPEED
- name: CD
['DVD', ['SPEED']]
- contents: ['SPEED']
  - name: SPEED
- name: DVD

【讨论】：