how to explicitly write two references in ruamel.yaml - ruamel.yaml

Question

If I have multiple references and when I write them to a YAML file using ruaml.yaml from Python I get:
<<: [*name-name, *help-name]
but instead I would prefer to have
<<: *name-name
<<: *help-name
Is there an option to achieve this while writing to the file?
UPDATE
descriptions:
- &description-one-ref
description: >
helptexts:
- &help-one
help_text: |
questions:
- &question-one
title: "title test"
reference: "question-one-ref"
field: "ChoiceField"
choices:
- "Yes"
- "No"
required: true
<<: *description-one-ref
<<: *help-one
riskvalue_max: 10
calculations:
- conditions:
- comparator: "equal"
value: "Yes"
actions:
- riskvalue: 0
- conditions:
- comparator: "equal"
value: "No"
actions:
- riskvalue: 10
Currently I'm reading such a file and modify specific values within python and then want to write it back. When I'm writing I'm getting the issue that the references are as list and not as outlined.
That means the workflow is as: I'm reading the doc via
yaml = ruamel.yaml.YAML()
with open('test.yaml') as f:
data = yaml.load(f)
for k in data.keys():
if k == 'questions':
q = data.get(k)
for i in range(0, len(q)):
q[i]['title'] = "my new title"
f.close()
g = open('new_file.yaml', 'w')
yaml(data)
g.close()

Answer 1

No, there is no such option, as it would lead to an invalid YAML file.
The << is a mapping key, for which the value is interpreted
specially assuming the parser implements to the language independent
merge key specification. And a mapping key must be unique
according to the YAML specification:
The content of a mapping node is an unordered set of key: value node
pairs, with the restriction that each of the keys is unique.
That ruamel.yaml (< 0.15.75) doesn't throw an error on such
duplicate key is a bug. On duplicate normal keys, ruamel.yaml
does throw an error. The bug is inherited from PyYAML (which is not
specification conformant, and does not throw an error even on
duplicate normal keys).
However with a little pre- and post-processing what you want to do can
be easily achieved. The trick is to make the YAML valid before parsing
by making the offending duplicate << keys unique (but recognisable)
and then, when writing the YAML back to file, substituting these
unique keys by <<: * again. In the following the first occurence of
<<: * is replaced by [<<, 0]:, the second by [<<, 1]: etc.
The * needs to be part of the substitution, as there are no anchors in
the document for those aliases.
import sys
import subprocess
import ruamel.yaml
yaml = ruamel.yaml.YAML()
yaml.preserve_quotes = True
yaml.indent(sequence=4, offset=2)
class DoubleMergeKeyEnabler(object):
def __init__(self):
self.pat = '<<: ' # could be at the root level mapping, so no leading space
self.r_pat = '[<<, {}]: ' # probably not using sequences as keys
self.pat_nr = -1
def convert(self, doc):
while self.pat in doc:
self.pat_nr += 1
doc = doc.replace(self.pat, self.r_pat.format(self.pat_nr), 1)
return doc
def revert(self, doc):
while self.pat_nr >= 0:
doc = doc.replace(self.r_pat.format(self.pat_nr), self.pat, 1)
self.pat_nr -= 1
return doc
dmke = DoubleMergeKeyEnabler()
with open('test.yaml') as fp:
# we don't do this line by line, that would not work well on flow style mappings
orgdoc = fp.read()
doc = dmke.convert(orgdoc)
data = yaml.load(doc)
data['questions'][0].anchor.always_dump = True
#######################################
# >>>> do your thing on data here <<< #
#######################################
with open('output.yaml', 'w') as fp:
yaml.dump(data, fp, transform=dmke.revert)
res = subprocess.check_output(['diff', '-u', 'test.yaml', 'output.yaml']).decode('utf-8')
print('diff says:', res)
which gives:
diff says:
which means the files are the same on round-trip (as long as you don't
change anything before dumping).
Setting preserve_quotes and calling ident() on the YAML instance are necessary to
preserve your superfluous quotes, resp. keeping the indentation.
Since the anchor question-one has no alias, you need to enable dumping explicitly by
setting always_dump on that attribute to True. If necessary you can recursively
walk over data and set anchor.always_dump = True when .anchor.value is not None