Save/dump a YAML file with comments in PyYAML

Question

I have a yaml file that looks like this:

# The following key opens a door key: value 

Is there a way I can load and dump this data while maintaining the comment?

Answer 1

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}

Answer 2

PyYAML throws away comments at a very low level (in Scanner.scan_to_next_token).

While you could adapt or extend it to handle comments in its whole stack, this would be a major modification. Dumping (=emitting) comments seems to be easier and was discussed in ticket 114 on the old PyYAML bug tracker.

As of 2020, the feature request about adding support for loading comments is still stalling.