Multiline strings are ugly after dumping

>>> lines = """
... a
... b
... c
... """
>>> lines
'\na\nb\nc\n'
>>> print(yaml.dump({'a': lines}, default_flow_style=False))
a: '

  a

  b

  c

  '

>>> # although roundtrip of dump-load is correct
>>> yaml.load(yaml.dump({'a': lines}))
{'a': '\na\nb\nc\n'}

This could output much shorter

a: |
  a
  b
  c

[jgunstone]

found this on StackOverflow as a quick fix for my requirement:

parsed = {'fdir_root': '/mnt/c/engDev/git_mf/ipyrun/tests/examples/line_graph_batch',
 'fpth_config': '/mnt/c/engDev/git_mf/ipyrun/tests/examples/line_graph_batch/config-shell_handler.json',
 'title': '# Plot Straight Lines\n### example RunApp',
 'configs': []}

import yaml
def str_presenter(dumper, data):
    """configures yaml for dumping multiline strings
    Ref: https://stackoverflow.com/questions/8640959/how-can-i-control-what-scalar-form-pyyaml-uses-for-my-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)
yaml.representer.SafeRepresenter.add_representer(str, str_presenter) # to use with safe_dum

s = yaml.dump(parsed, indent=2)  # , sort_keys=True)
print(s)

>>> configs: []
>>> fdir_root: /mnt/c/engDev/git_mf/ipyrun/tests/examples/line_graph_batch
>>> fpth_config: /mnt/c/engDev/git_mf/ipyrun/tests/examples/line_graph_batch/config-shell_handler.json
>>> title: |-
>>>   # Plot Straight Lines
>>>   ### example RunApp

[cjw296]

Slight tweak, better handles strings ending in a newline and might be a bit faster:

def str_presenter(dumper, data):
    """configures yaml for dumping multiline strings
    Ref: https://stackoverflow.com/questions/8640959/how-can-i-control-what-scalar-form-pyyaml-uses-for-my-data"""
    if data.count('\n') > 0:  # 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)