ruamel.yaml - indent sequences not working?

Question

MWE:

import sys
from ruamel.yaml import YAML
yaml = YAML(typ='safe')
yaml.default_flow_style = False
yaml.indent(sequence=4, mapping=2, offset=2)
d = {
    'name': 'asdf',
    'types': [
        1,
        2,
    ],
    'class': 1,
}
import sys
yaml.dump(d, sys.stdout)
>>>
class: 1
name: asdf
types:
- 1
- 2

I expected types to have an indent before the - entries -- why is this not so? The docs are fairly scarce, and the yaml.indent method seems to have no effect here no matter the combination of values I try...

py 3.6.4 / winx64, ruamel 0.15.35

Answer 1

The reason that this doesn't work is because you use typ='safe' which gives you the SafeLoader() and that doesn't support the indentation difference between sequences and mappings. It is provided by the (default) round-trip-loader (which is a subclass of the "normal" SafeLoader())

So just change:

yaml = YAML(typ='safe')

to

yaml = YAML()

or

yaml = YAML(typ='rt')

If you want to round-trip-this and have normal dicts and lists in your program, instead of the comment preserving CommentedMap() and CommentedList() subclasses thereof, you can do:

import sys
import ruamel.yaml

yaml_str = """\
class: 1
name: asdf
types:
  - 1
  - 2
"""

yamll = ruamel.yaml.YAML(typ='safe')
yamld = ruamel.yaml.YAML()
yamld.indent(mapping=4, sequence=4, offset=2)
data = yamll.load(yaml_str)
assert type(data) == dict
yamld.dump(data, sys.stdout)