PEG NodeVisitor

Question

Представьте себе маленькую грамматику PEG, такую ​​как

from parsimonious.grammar import Grammar
from parsimonious.nodes import NodeVisitor

grammar = Grammar(
    r"""
    term    = lpar (number comma? ws?)+ rpar
    number  = ~"\d+"
    lpar    = "("
    rpar    = ")"
    comma   = ","
    ws      = ~"\s*"
    """
)

tree = grammar.parse("(5, 4, 3)")
print(tree)

Какие выходные данные

<Node called "term" matching "(5, 4, 3)">
    <Node called "lpar" matching "(">
    <Node matching "5, 4, 3">
        <Node matching "5, ">
            <RegexNode called "number" matching "5">
            <Node matching ",">
                <Node called "comma" matching ",">
            <Node matching " ">
                <RegexNode called "ws" matching " ">
        <Node matching "4, ">
            <RegexNode called "number" matching "4">
            <Node matching ",">
                <Node called "comma" matching ",">
            <Node matching " ">
                <RegexNode called "ws" matching " ">
        <Node matching "3">
            <RegexNode called "number" matching "3">
            <Node matching "">
            <Node matching "">
                <RegexNode called "ws" matching "">
    <Node called "rpar" matching ")">

Как получить number регулярное выражение из term в этом примере?Я знаю, что могу использовать класс NodeVisitor и исследовать каждое число, но я хотел бы получить часть регулярного выражения из term.

Answer 1

Вероятно, лучше использовать класс NodeVisitor и идти по этому пути, но вот еще одно простое решение:

from parsimonious.grammar import Grammar
from parsimonious.nodes import NodeVisitor

grammar = Grammar(
    r"""
    term    = lpar (number comma? ws?)+ rpar
    number  = ~"\d+"
    lpar    = "("
    rpar    = ")"
    comma   = ","
    ws      = ~"\s*"
    """
)

tree = grammar.parse("(5, 4, 3)")

def walk(node):
    if node.expr_name == 'number':
        print(node)
    for child in node.children:
        walk(child)

walk(tree)

# <RegexNode called "number" matching "5">
# <RegexNode called "number" matching "4">
# <RegexNode called "number" matching "3">