How can I control what scalar form PyYAML uses for my data?

Falling in love with @lbt's approach, I got this code:

import yamldef str_presenter(dumper, data):  if len(data.splitlines()) > 1:  # check for multiline string    return dumper.represent_scalar('tag:yaml.org,2002:str', data, style='|')  return dumper.represent_scalar('tag:yaml.org,2002:str', data)yaml.add_representer(str, str_presenter)# to use with safe_dump:yaml.representer.SafeRepresenter.add_representer(str, str_presenter)

It makes every multiline string be a block literal.

I was trying to avoid the monkey patching part.Full credit to @lbt and @J.F.Sebastian.

Based on Any yaml libraries in Python that support dumping of long strings as block literals or folded blocks?

import yamlfrom collections import OrderedDictclass quoted(str):    passdef quoted_presenter(dumper, data):    return dumper.represent_scalar('tag:yaml.org,2002:str', data, style='"')yaml.add_representer(quoted, quoted_presenter)class literal(str):    passdef literal_presenter(dumper, data):    return dumper.represent_scalar('tag:yaml.org,2002:str', data, style='|')yaml.add_representer(literal, literal_presenter)def ordered_dict_presenter(dumper, data):    return dumper.represent_dict(data.items())yaml.add_representer(OrderedDict, ordered_dict_presenter)d = OrderedDict(short=quoted("Hello"), long=literal("Line1\nLine2\nLine3\n"))print(yaml.dump(d))

Output

short: "Hello"long: |  Line1  Line2  Line3

I wanted any input with a \n in it to be a block literal. Using the code in yaml/representer.py as a base I got:

# -*- coding: utf-8 -*-import yamldef should_use_block(value):    for c in u"\u000a\u000d\u001c\u001d\u001e\u0085\u2028\u2029":        if c in value:            return True    return Falsedef my_represent_scalar(self, tag, value, style=None):    if style is None:        if should_use_block(value):             style='|'        else:            style = self.default_style    node = yaml.representer.ScalarNode(tag, value, style=style)    if self.alias_key is not None:        self.represented_objects[self.alias_key] = node    return nodea={'short': "Hello", 'multiline': """Line1Line2Line3""", 'multiline-unicode': u"""Lêne1Lêne2Lêne3"""}print(yaml.dump(a))print(yaml.dump(a, allow_unicode=True))yaml.representer.BaseRepresenter.represent_scalar = my_represent_scalarprint(yaml.dump(a))print(yaml.dump(a, allow_unicode=True))

Output

{multiline: 'Line1    Line2    Line3    ', multiline-unicode: "L\xEAne1\nL\xEAne2\nL\xEAne3\n", short: Hello}{multiline: 'Line1    Line2    Line3    ', multiline-unicode: 'Lêne1    Lêne2    Lêne3    ', short: Hello}After overridemultiline: |  Line1  Line2  Line3multiline-unicode: "L\xEAne1\nL\xEAne2\nL\xEAne3\n"short: Hellomultiline: |  Line1  Line2  Line3multiline-unicode: |  Lêne1  Lêne2  Lêne3short: Hello