C # parse and modify strings in yaml

Most YAML parsers are built to read YAML, either written by other programs or edited by humans, and to write YAML to be read by other programs. What is known to be missing is the ability of parsers to write YAML, which is still human readable:

• display order of keys is undefined
• comments are discarded
• scalar block literal style, if present, is discarded
• distance around scalars is discarded
• scalar folding information, if any, is discarded

Loading a dump of an uploaded YAML file with manual processing will create the same internal data structures as the main load, but the intermediate dump usually does not look like the original (manual) YAML.

If you have a Python program:

import ruamel.yaml as yaml

yaml_str = """\
receipt:     Oz-Ware Purchase Invoice
date:        2007-08-06
customer:
    given:   Dorothy

items:
    - part_no:   A4786
      descrip:   Water Bucket (Filled)

    - part_no:   E1628
      descrip:   High Heeled "Ruby" Slippers
      size:      8

bill-to:  &id001
    street: |
            123 Tornado Alley
            Suite 16
    city:   East Centerville
    state:  KS

ship-to:  *id001

specialDelivery:  >
    Follow the Yellow Brick
    Road to the Emerald City.
"""

data1 = yaml.load(yaml_str, Loader=yaml.Loader)
dump_str = yaml.dump(data1, Dumper=yaml.Dumper)
data2 = yaml.load(dump_str, Loader=yaml.Loader)

      

        
        
        
      

    

Then the following statements hold:

assert data1 == data2
assert dump_str != yaml_str

      

        
        
        
      

    

The intermediate dump_str

looks like this:

bill-to: &id001 {city: East Centerville, state: KS, street: '123 Tornado Alley

    Suite 16

    '}
customer: {given: Dorothy}
date: 2007-08-06
items:
- {descrip: Water Bucket (Filled), part_no: A4786}
- {descrip: High Heeled "Ruby" Slippers, part_no: E1628, size: 8}
receipt: Oz-Ware Purchase Invoice
ship-to: *id001
specialDelivery: 'Follow the Yellow Brick Road to the Emerald City.

  '

      

        
        
        
      

    

The above is the default behavior for ruamel.yaml , PyYAML, and for many other YAML parsers in other languages ​​and online YAML conversion services. For some parsers, this is the only behavior.

The reason for running ruamel.yaml as an enhancement to PyYAML was to make the transition from manual YAML to internal data, to YAML, lead to something that is better human readable (what I call a round trip) and saves additional information (especially comments).

data = yaml.load(yaml_str, Loader=yaml.RoundTripLoader)
print yaml.dump(data, Dumper=yaml.RoundTripDumper)

      

        
        
        
      

    

gives you:

receipt: Oz-Ware Purchase Invoice
date: 2007-08-06
customer:
  given: Dorothy
items:
- part_no: A4786
  descrip: Water Bucket (Filled)
- part_no: E1628
  descrip: High Heeled "Ruby" Slippers
  size: 8
bill-to: &id001
  street: |
    123 Tornado Alley
    Suite 16
  city: East Centerville
  state: KS
ship-to: *id001
specialDelivery: 'Follow the Yellow Brick Road to the Emerald City.

  '

      

        
        
        
      

    

My focus was on comments, key, orderly and literal block style. The distance between scalars and stacked scalars is not (yet) special.

From now on (you can also do this in PyYAML, but you won't have the built-in enhancements to ruamel.yaml key management), you can either provide custom emitters or hook into the system at a lower level by overriding some of the methods in emitter.py

(and making sure you can call originals for cases you don't need to handle:

def rewrite_write_plain(self, text, split=True):
    if self.state == self.expect_block_mapping_simple_value:
        text = '###' + text + '###'
        while self.column < 20:
            text = ' ' + text
            self.column += 1
    self._org_write_plain(text, split)

def rewrite_write_literal(self, text):
    if self.state == self.expect_block_mapping_simple_value:
        last_nl = False
        if text and text[-1] == '\n':
            last_nl = True
            text = text[:-1]
        text = '###' + text + '###'
        if False:
            extra_indent = ''
            while self.column < 15:
                text = ' ' + text
                extra_indent += ' '
                self.column += 1
            text = text.replace('\n', '\n' + extra_indent)
        if last_nl:
            text += '\n'
    self._org_write_literal(text)

def rewrite_write_single_quoted(self, text, split=True):
    if self.state == self.expect_block_mapping_simple_value:
        last_nl = False
        if text and text[-1] == u'\n':
            last_nl = True
            text = text[:-1]
        text = u'###' + text + u'###'
        if last_nl:
            text += u'\n'
    self.write_folded(text)

def rewrite_write_indicator(self, indicator, need_whitespace,
                    whitespace=False, indention=False):
    if indicator and indicator[0] in u"*&":
        indicator = u'###' + indicator + u'###'
        while self.column < 20:
            indicator = ' ' + indicator
            self.column += 1
    self._org_write_indicator(indicator, need_whitespace, whitespace,
                              indention)

dumper._org_write_plain = dumper.write_plain
dumper.write_plain = rewrite_write_plain
dumper._org_write_literal = dumper.write_literal
dumper.write_literal = rewrite_write_literal
dumper._org_write_single_quoted = dumper.write_single_quoted
dumper.write_single_quoted = rewrite_write_single_quoted
dumper._org_write_indicator = dumper.write_indicator
dumper.write_indicator = rewrite_write_indicator

print yaml.dump(data, Dumper=dumper, indent=4)

      

        
        
        
      

    

gives you:

receipt:             ###Oz-Ware Purchase Invoice###
date:                ###2007-08-06###
customer:
    given:           ###Dorothy###
items:
-   part_no:         ###A4786###
    descrip:         ###Water Bucket (Filled)###
-   part_no:         ###E1628###
    descrip:         ###High Heeled "Ruby" Slippers###
    size:            ###8###
bill-to:             ###&id001###
    street: |
        ###123 Tornado Alley
        Suite 16###
    city:            ###East Centerville###
    state:           ###KS###
ship-to:             ###*id001###
specialDelivery: >
    ###Follow the Yellow Brick Road to the Emerald City.###

      

        
        
        
      

    

which is hopefully acceptable for further processing in C #