高级Python正则表达式:如何从多行字符串中评估和提取嵌套列表和数字？

保存为text2json.js或类似的东西,并将一些文本重定向(或管道):

# input redirection (this works on Windows, too)
node text2json.js  output.json

# common alternative, but I'd recommend input redirection over this
cat input.txt | node text2json.js > output.json

还有用于Python的PEG解析器生成器,例如https://github.com/erikrose/parsimonious.解析器创建语言在实现之间有所不同,因此上面只能用于peg.js,但原理完全相同.

编辑我已经挖到Parsimonious并在Python代码中重新创建了上述解决方案.方法是相同的,解析器语法是相同的,只有一些微小的语法变化.

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

grammar = Grammar(
    r"""
    document   = line*
    line       = whitespace? item (whitespace item)* whitespace? eol
    item       = group / number / boolean / string
    group      = "[" item (comma item)* whitespace? "]"
    comma      = whitespace? "," whitespace?
    number     = "NaN" / ~"[0-9.]+"
    boolean    = "True" / "False"
    string     = ~"[^ 0-9\[\]\r\n,][^ \[\]\r\n,]*"
    whitespace = ~" +"
    eol        = ~"\r?\n" / eof
    eof        = ~"$"
    """)

class DataExtractor(NodeVisitor):
    @staticmethod
    def concat_items(first_item, remaining_items):
        """ helper to concat the values of delimited items (lines or goups) """
        return first_item + list(map(lambda i: i[1][0], remaining_items))

    def generic_visit(self, node, processed_children):
        """ in general we just want to see the processed children of any node """
        return processed_children

    def visit_line(self, node, processed_children):
        """ line nodes return an array of their processed_children """
        _, first_item, remaining_items, _, _ = processed_children
        return self.concat_items(first_item, remaining_items)

    def visit_group(self, node, processed_children):
        """ group nodes return an array of their processed_children """
        _, first_item, remaining_items, _, _ = processed_children
        return self.concat_items(first_item, remaining_items)

    def visit_number(self, node, processed_children):
        """ number nodes return floats (nan is a special value of floats) """
        return float(node.text)

    def visit_boolean(self, node, processed_children):
        """ boolean nodes return return True or False """
        return node.text == "True"

    def visit_string(self, node, processed_children):
        """ string nodes just return their own text """
        return node.text

该DataExtractor负责遍历树和节点拉出数据,返回一个字符串,数字,布尔值,或NaN的名单.

该concat_items()函数执行与list()上述Javascript代码中的函数相同的任务,其他函数也在peg.js方法中具有等价物,除了peg.js将它们直接集成到解析器定义中,而Parsimonious期望在单独的类中定义,所以相比之下它有点晦涩,但也不算太糟糕.

用法,假设一个名为"data.txt"的输入文件,也反映了JS代码:

de = DataExtractor()

with open("data.txt", encoding="utf8") as f:
    text = f.read()

tree = grammar.parse(text)
data = de.visit(tree)
print(data)

输入:

orig shifted not_equal cumsum lst
0 10 NaN True 1 [[10, 10.4], [c, 10, eee]]
1 10 10.0 False 1 [[10, 10.4], [c, 10, eee]]
2 23 10.0 True 2 [[10, 10.4], [c, 10, eee]]

输出:

[
    ['orig', 'shifted', 'not_equal', 'cumsum', 'lst'],
    [0.0, 10.0, nan, True, 1.0, [[10.0, 10.4], ['c', 10.0, 'eee']]],
    [1.0, 10.0, 10.0, False, 1.0, [[10.0, 10.4], ['c', 10.0, 'eee']]], 
    [2.0, 23.0, 10.0, True, 2.0, [[10.0, 10.4], ['c', 10.0, 'eee']]]
]

从长远来看,我希望这种方法比正则表达式hackery更易于维护和灵活.添加对NaN和布尔值的明确支持(例如上面的peg.js-Solution没有 - 它们被解析为字符串)很容易.

正如评论中所指出的,这个任务与正则表达式无关.正则表达式从根本上说无法处理嵌套结构.你需要的是一个解析器.

创建解析器的方法之一是PEG,它允许您以声明性语言设置令牌列表及其相互之间的关系.然后将此解析器定义转换为可以处理所描述的输入的实际解析器.解析成功后,您将获得一个树结构,其中所有项都已正确嵌套.

出于演示目的,我使用了Javascript实现peg.js,它有一个在线演示页面,您可以根据某些输入对解析器进行实时测试.这个解析器定义:

{
    // [value, [[delimiter, value], ...]] => [value, value, ...]
    const list = values => [values[0]].concat(values[1].map(i => i[1]));
}
document
    = line*
line "line"
    = value:(item (whitespace item)*) whitespace? eol { return list(value) }
item "item"
    = number / string / group
group "group"
    = "[" value:(item (comma item)*) whitespace? "]" { return list(value) }
comma "comma"
    = whitespace? "," whitespace?
number "number"
    = value:$[0-9.]+ { return +value }
string "string"
    = $([^ 0-9\[\]\r\n,] [^ \[\]\r\n,]*)
whitespace "whitespace"
    = $" "+
eol "eol"
    = [\r]? [\n] / eof
eof "eof"
    = !.

可以理解这种输入:

c0 c1 c2 c3 c4 c5
0   10 100.5 [1.5, 2]     [[10, 10.4], [c, 10, eee]]  [[a , bg], [5.5, ddd, edd]]
1   20 200.5 [2.5, 2]     [[20, 20.4], [d, 20, eee]]  [[a , bg], [7.5, udd, edd1]]

并生成此对象树(JSON表示法):

[
    ["c0", "c1", "c2", "c3", "c4", "c5"],
    [0, 10, 100.5, [1.5, 2], [[10, 10.4], ["c", 10, "eee"]], [["a", "bg"], [5.5, "ddd", "edd"]]],
    [1, 20, 200.5, [2.5, 2], [[20, 20.4], ["d", 20, "eee"]], [["a", "bg"], [7.5, "udd", "edd1"]]]
]

即

一系列的线条,

每个都是一个值数组,

每个都可以是数字,字符串或其他值数组

然后,您的程序可以处理此树结构.

上面的例子可以用node.js将您的输入转换为JSON.以下最小JS程序接受来自STDIN的数据并将解析后的结果写入STDOUT:

// reference the parser.js file, e.g. downloaded from https://pegjs.org/online
const parser = require('./parser');

var chunks = [];

// handle STDIN events to slurp up all the input into one big string
process.stdin.on('data', buffer => chunks.push(buffer.toString()));
process.stdin.on('end', function () {
    var text = chunks.join('');
    var data = parser.parse(text);
    var json = JSON.stringify(data, null, 4);
    process.stdout.write(json);
});

// start reading from STDIN
process.stdin.resume();

# input redirection (this works on Windows, too)
node text2json.js  output.json

# common alternative, but I'd recommend input redirection over this
cat input.txt | node text2json.js > output.json

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

grammar = Grammar(
    r"""
    document   = line*
    line       = whitespace? item (whitespace item)* whitespace? eol
    item       = group / number / boolean / string
    group      = "[" item (comma item)* whitespace? "]"
    comma      = whitespace? "," whitespace?
    number     = "NaN" / ~"[0-9.]+"
    boolean    = "True" / "False"
    string     = ~"[^ 0-9\[\]\r\n,][^ \[\]\r\n,]*"
    whitespace = ~" +"
    eol        = ~"\r?\n" / eof
    eof        = ~"$"
    """)

class DataExtractor(NodeVisitor):
    @staticmethod
    def concat_items(first_item, remaining_items):
        """ helper to concat the values of delimited items (lines or goups) """
        return first_item + list(map(lambda i: i[1][0], remaining_items))

    def generic_visit(self, node, processed_children):
        """ in general we just want to see the processed children of any node """
        return processed_children

    def visit_line(self, node, processed_children):
        """ line nodes return an array of their processed_children """
        _, first_item, remaining_items, _, _ = processed_children
        return self.concat_items(first_item, remaining_items)

    def visit_group(self, node, processed_children):
        """ group nodes return an array of their processed_children """
        _, first_item, remaining_items, _, _ = processed_children
        return self.concat_items(first_item, remaining_items)

    def visit_number(self, node, processed_children):
        """ number nodes return floats (nan is a special value of floats) """
        return float(node.text)

    def visit_boolean(self, node, processed_children):
        """ boolean nodes return return True or False """
        return node.text == "True"

    def visit_string(self, node, processed_children):
        """ string nodes just return their own text """
        return node.text

de = DataExtractor()

with open("data.txt", encoding="utf8") as f:
    text = f.read()

tree = grammar.parse(text)
data = de.visit(tree)
print(data)

orig shifted not_equal cumsum lst
0 10 NaN True 1 [[10, 10.4], [c, 10, eee]]
1 10 10.0 False 1 [[10, 10.4], [c, 10, eee]]
2 23 10.0 True 2 [[10, 10.4], [c, 10, eee]]

[
    ['orig', 'shifted', 'not_equal', 'cumsum', 'lst'],
    [0.0, 10.0, nan, True, 1.0, [[10.0, 10.4], ['c', 10.0, 'eee']]],
    [1.0, 10.0, 10.0, False, 1.0, [[10.0, 10.4], ['c', 10.0, 'eee']]], 
    [2.0, 23.0, 10.0, True, 2.0, [[10.0, 10.4], ['c', 10.0, 'eee']]]
]