Differences with PyYAML

If I have seen further, it is by standing on the shoulders of giants.
                                                  Isaac Newton (1676)

ruamel.yaml is a derivative of Kirill Simonov’s PyYAML 3.11 and would not exist without that excellent base to start from.

The following a summary of the major differences with PyYAML 3.11

Defaulting to YAML 1.2 support

PyYAML supports the YAML 1.1 standard, ruamel.yaml supports YAML 1.2 as released in 2009.

  • YAML 1.2 dropped support for several features unquoted Yes, No, On, Off
  • YAML 1.2 no longer accepts strings that start with a 0 and solely consist of number characters as octal, you need to specify such strings with 0o[0-7]+ (zero + lower-case o for octal + one or more octal characters).
  • YAML 1.2 no longer supports sexagesimals, so the string scalar 12:34:56 doesn’t need quoting.
  • \/ escape for JSON compatibility
  • correct parsing of floating point scalars with exponentials

unless the YAML document is loaded with an explicit version==1.1 or the document starts with:

% YAML 1.1

, ruamel.yaml will load the document as version 1.2.

PY2/PY3 reintegration

ruamel.yaml re-integrates the Python 2 and 3 sources, running on Python 2.6, 2.7 (CPython, PyPy), 3.3, 3.4, 3.5. It is more easy to extend and maintain as only a miniscule part of the code is version specific.


  • ruamel.yaml follows the indent keyword argument on scalars when dumping.


ruamel.yaml is tested using tox and py.test. In addition to new tests the original PyYAML test framework is called from within tox runs.

Before versions are pushed to PyPI, tox is invoked, and has to pass, on all Python versions, PyPI as well as flake8/pep8