如何从 Python 中的 YAML 文件创建树数据结构？

Question

Suppose I have a YAML file as follows:

template:
 artifacts:
  config:
   a: value1
   b: value2
  jars:
   a: value1
   b: value2
  scripts:
   a: value1
   b: value2

I would like to have it like a tree as below:

template--
          |__artifacts__
                        |__config__
                        |          |__a__
                        |          |     |__value1
                        |          |
                        |          |__b__
                        |                |__value2
                        |__jars__ ...

How can I do that?

Answer 1

There are multiple parsers for YAML available for Python, but the only one supporting the latest YAML specification (1.2, released in 2009) is ruamel.yaml (disclaimer: I am the author of that package). The other packages (PySyck, PyYAML) also do not support loading of valid YAML constructs such as sequences/mappings as mapping keys. ruamel.yaml can be directed to dump YAML 1.1 for those outdated packages that only support that version of the YAML specification.

Nested python dict s can be used as a tree structure, with the keys a value of a node and the values that are non- dict s leaf nodes. This is the datastructure that is loaded from the mappings in your YAML file.

from pathlib import Path
from pprint import pprint
import ruamel.yaml

input = Path('input.yaml')
yaml = ruamel.yaml.YAML()
data = yaml.load(input)
pprint(data)

which gives:

{'template': {'artifacts': {'config': {'a': 'value1',
                                       'b': 'value2'},
                            'jars': {'a': 'value1',
                                     'b': 'value2'},
                            'scripts': {'a': 'value1',
                                        'b': 'value2'}}}}

This doesn't look like your expected output, nor are dicts really a tree structure. You can of course walk over your data -structure and create a tree of Node s, but that is a bit backward, as you can tell the parser to directly create a Node when building the tree.

import sys
from ruamel.yaml.constructor import SafeConstructor

class Node:
    # your node definition here
    pass


class MyConstructor(SafeConstructor):
    def construct_yaml_map(self, node):
        data = Node()
        yield data
        res = self.construct_mapping(node)
        # and update data with the parsed data

MyConstructor.add_constructor('tag:yaml.org,2002:map', 
                              MyConstructor.construct_yaml_map)


yaml = ruamel.yaml.YAML()
yaml.Constructor = MyConstructor
data = yaml.load(input)

Please note that the above automatically deals with recursive structures in your YAML file, something not as easily realised when walking over the YAML loaded in the normal way.