Парсинг, изменение и сохранение yaml с помощью ruamel.yaml

result.yaml

# file comment

invoice: 34843
date: 2001-01-23
# Русский коммент
bill-to: &id001
  given: Джон
  family: Коннор

  address:
    lines: |
      458 Walkman Dr.
      Suite #292
    city: Royal Oak            # inline comment
    state: MI
    postal: 48046

# block comment
  new item: '12312'
ship-to: *id001
product:
  - sku: [BL394D, BUBU1245]
    quantity: 4

      # item comment
    description: Basketball

    price: 450.00
  - sku: BL4438H
    quantity: 1
    description: 'Super Hoop'
    price: 2392.00

  - '12312'
tax: 251.42

total: 4443.52

comments: >
  Late afternoon is best.
  Backup contact is Nancy
  Billsmer @ 338-4338.

flow sequence: [FlowEntryToken, 'FlowEntryToken', '12312']
flow mapping: {KeyToken: ValueToken}

run.py

# Обычный pyyaml не сохраняет переводы строк и комментарии
import ruamel.yaml


def update_yaml(source_path, dest_path=None, processor=None):
    yaml = ruamel.yaml.YAML()
    yaml.default_flow_style = False
    yaml.preserve_quotes = True
    yaml.indent(mapping=2, sequence=4, offset=2)

    with open(source_path, 'r') as file: 
        data = yaml.load(file)
        file.close()

    processor(data)

    if dest_path is not None:
        with open(dest_path, 'w') as dest_file: 
            yaml.dump(data, dest_file)
            dest_file.close()

    return data, yaml


def processor(data):
    data['bill-to']['new item'] = '12312'   # :-/
    data['flow sequence'].append('12312')
    data['product'].append('12312')         # :-/


data, yaml = update_yaml('source.yaml', 'result.yaml', processor=processor)
print(data)

source.yaml

# file comment

invoice: 34843
date   : 2001-01-23
# Русский коммент
bill-to: &id001
    given  : Джон
    family : Коннор

    address:
        lines: |
            458 Walkman Dr.
            Suite #292
        city    : Royal Oak    # inline comment
        state   : MI
        postal  : 48046

# block comment
ship-to: *id001
product:
    - sku         : [BL394D, BUBU1245]
      quantity    : 4

      # item comment
      description : Basketball

      price       : 450.00
    - sku         : BL4438H
      quantity    : 1
      description : 'Super Hoop'
      price       : 2392.00

tax  : 251.42

total: 4443.52

comments: >
    Late afternoon is best.
    Backup contact is Nancy
    Billsmer @ 338-4338.

flow sequence: [FlowEntryToken, 'FlowEntryToken']
flow mapping: {KeyToken: ValueToken}