python中的Antlr 4没有按预期工作(试图解析一本书的章节和段落)

Question

我想创建一个非常简单的ANTLR4解析器(在Python中(，没有监听器和访问者，它以任何顺序输入书籍的章节和段落，并返回条目的high_level(章节(和low_level(段落(，例如，如果我输入2 a或a 2，它应该打印">第2章a段"；。

这是我的Example.g4

grammar Example;
text
    : paragraph ;
paragraph
    : high_level (WS low_level)?
    | low_level WS high_level
    ;
low_level
    : 'a' | 'b'  | 'c'  ;
high_level
    : '1'  | '2'  | '3';
WS : [ trn]+ ;

我在航站楼里做这个java -jar ~/antlr-4.8-complete.jar -Dlanguage=Python3 -no-listener -no-visitor Example.g4

它生成了两个python文件，然后我编写了以下python脚本

from antlr4 import *
from ExampleLexer import ExampleLexer
from ExampleParser import ExampleParser

def main():
    while True:
        text = InputStream(input(">"))
        lexer = ExampleLexer(text)
        stream = CommonTokenStream(lexer)
        parser = ExampleParser(stream)
        tree = parser.text()
        query = tree.paragraph()
        low_level = query.low_level()
        high_level = query.high_level()
        print(f"chapter {high_level}, paragraph {low_level}")

if __name__ == '__main__':
    main()

然而，如果我运行它并输入2 a，我会得到chapter [10 8], paragraph [12 8]

有人能解释一下我做错了什么吗？我不懂方括号里的数字。

Answer 1

这只是RuleContext显示的一些调试信息(生成的Low_levelContext和High_levelContext类从中扩展(。在您的情况下，将显示规则的invokingState和parentCtx。

看看来源：

class RuleContext(RuleNode):
    ...
    def __str__(self):
        return self.toString(None, None)
    ...
    def toString(self, ruleNames:list, stop:RuleContext)->str:
        with StringIO() as buf:
            p = self
            buf.write("[")
            while p is not None and p is not stop:
                if ruleNames is None:
                    if not p.isEmpty():
                        buf.write(str(p.invokingState))
                else:
                    ri = p.getRuleIndex()
                    ruleName = ruleNames[ri] if ri >= 0 and ri < len(ruleNames) else str(ri)
                    buf.write(ruleName)
                if p.parentCtx is not None and (ruleNames is not None or not p.parentCtx.isEmpty()):
                    buf.write(" ")
                p = p.parentCtx
            buf.write("]")
            return buf.getvalue()
    ...

https://github.com/antlr/antlr4/blob/master/runtime/Python3/src/antlr4/RuleContext.py

你没有解释你想显示什么，但我猜规则匹配的文本，在这种情况下，你可以这样做：

print(f"chapter {high_level.getText()}, paragraph {low_level.getText()}")