将BNF语法转换为pyparsing

Question

如何使用正则表达式(或pyparsing更好？)来描述下面提供的脚本语言(Backus-Naur Form):

<root>   :=     <tree> | <leaves>
<tree>   :=     <group> [* <group>] 
<group>  :=     "{" <leaves> "}" | <leaf>;
<leaves> :=     {<leaf>;} leaf
<leaf>   :=     <name> = <expression>{;}

<name>          := <string_without_spaces_and_tabs>
<expression>    := <string_without_spaces_and_tabs>

脚本示例:

{
 stage = 3;
 some.param1 = [10, 20];
} *
{
 stage = 4;
 param3 = [100,150,200,250,300]
} *
 endparam = [0, 1]

我使用python re.compile并希望将所有内容分组,如下所示:

[ [ 'stage',       '3'],
  [ 'some.param1', '[10, 20]'] ],

[ ['stage',  '4'],
  ['param3', '[100,150,200,250,300]'] ],

[ ['endparam', '[0, 1]'] ]

更新: 我发现pyparsing是更好的解决方案,而不是正则表达式.

Answer 1

Pyparsing允许您简化这些类型的构造

leaves :: {leaf} leaf

只是

OneOrMore(leaf)

所以你的BNF在pyparsing中的一种形式看起来像:

from pyparsing import *

LBRACE,RBRACE,EQ,SEMI = map(Suppress, "{}=;")
name = Word(printables, excludeChars="{}=;")
expr = Word(printables, excludeChars="{}=;") | quotedString

leaf = Group(name + EQ + expr + SEMI)
group = Group(LBRACE + ZeroOrMore(leaf) + RBRACE) | leaf
tree = OneOrMore(group)

我加入quotedString作为替代expr的,如果你想拥有的东西,也包括排除字符之一.并且在叶子和组周围添加组将保持支撑结构.

不幸的是,您的样本并不完全符合此BNF:

1. 在空间[10, 20]和[0, 1]让他们无效exprs

2. 有些叶子没有终止;s

3. 孤独的*人物 - ???

此示例使用上述解析器成功解析:

sample = """
{
 stage = 3;
 some.param1 = [10,20];
}
{
 stage = 4;
 param3 = [100,150,200,250,300];
}
 endparam = [0,1];
 """

parsed = tree.parseString(sample)    
parsed.pprint()

赠送:

[[['stage', '3'], ['some.param1', '[10,20]']],
 [['stage', '4'], ['param3', '[100,150,200,250,300]']],
 ['endparam', '[0,1]']]