Save/dump a YAML file with comments in PyYAML

If you are using block structured YAML, you can use the python package¹ ruamel.yaml which is a derivative of PyYAML and supports round trip preservation of comments:

import sys
import ruamel.yaml

yaml_str = """\
# example
name:
  # details
  family: Smith   # very common
  given: Alice    # one of the siblings
"""

yaml = ruamel.yaml.YAML()  # defaults to round-trip if no parameters given
code = yaml.load(yaml_str)
code['name']['given'] = 'Bob'

yaml.dump(code, sys.stdout)

with result:

# example
name:
  # details
  family: Smith   # very common
  given: Bob      # one of the siblings

Note that the end-of-line comments are still aligned.

Instead of normal list and dict objects the code consists of wrapped versions² on which the comments attached.

¹ _{Install with pip install ruamel.yaml. Works on Python 2.6/2.7/3.3+}

² _{ordereddict is used in case of a mapping, to preserve ordering}