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ruamel.yaml is a YAML parser/emitter that supports roundtrip preservation of comments, seq/map flow style, and map key order

Project description


``ruamel.yaml`` is a YAML 1.2 loader/dumper package for Python.

:version: 0.15.42
:updated: 2018-07-01

Starting with version 0.15.0 the way YAML files are loaded and dumped
is changing. See the API doc for details. Currently existing
functionality will throw a warning before being changed/removed.
**For production systems you should pin the version being used with
``ruamel.yaml<=0.15``**. There might be bug fixes in the 0.14 series,
but new functionality is likely only to be available via the new API.

If your package uses ``ruamel.yaml`` and is not listed on PyPI, drop
me an email, preferably with some infomormation on how you use the
package (or a link to bitbucket/github) and I'll keep you informed
when the status of the API is stable enough to make the transition.

* `Overview <>`_
* `Installing <>`_
* `Basic Usage <>`_
* `Details <>`_
* `Examples <>`_
* `API <>`_
* `Differences with PyYAML <>`_

.. image::

.. image::


.. should insert NEXT: at the beginning of line for next key (with empty line)

0.15.42 (2018-07-01):
- fix regression showing only on narrow Python 2.7 (py27mu) builds
(with help from
`Marcel Bargull <>`__ and
`Colm O'Connor <>`__).
- run pre-commit ``tox`` on Python 2.7 wide and narrow, as well as

0.15.41 (2018-06-27):
- add detection of C-compile failure (investigation prompted by
`StackOverlow <>`__ by
`Emmanuel Blot <>`__),
which was removed while no longer dependent on ``libyaml``, C-extensions
compilation still needs a compiler though.

0.15.40 (2018-06-18):
- added links to landing places as suggested in issue 190 by
`KostisA <>`__
- fixes issue #201: decoding unicode escaped tags on Python2, reported
by `Dan Abolafia <>`__

0.15.39 (2018-06-17):
- merge PR27 improving package startup time (and loading when regexp not
actually used), provided by
`Marcel Bargull <>`__

0.15.38 (2018-06-13):
- fix for losing precision when roundtripping floats by
`Rolf Wojtech <>`__
- fix for hardcoded dir separator not working for Windows by
`Nuno André <>`__
- typo fix by `Andrey Somov <>`__

0.15.37 (2018-03-21):
- again trying to create installable files for 187

0.15.36 (2018-02-07):
- fix issue 187, incompatibility of C extension with 3.7 (reported by
Daniel Blanchard)

0.15.35 (2017-12-03):
- allow ``None`` as stream when specifying ``transform`` parameters to
This is useful if the transforming function doesn't return a meaningful value
(inspired by `StackOverflow <>`__ by
`rsaw <>`__).

0.15.34 (2017-09-17):
- fix for issue 157: CDumper not dumping floats (reported by Jan Smitka)

0.15.33 (2017-08-31):
- support for "undefined" round-tripping tagged scalar objects (in addition to
tagged mapping object). Inspired by a use case presented by Matthew Patton
on `StackOverflow <>`__.
- fix issue 148: replace cryptic error message when using !!timestamp with an
incorrectly formatted or non- scalar. Reported by FichteFoll.

0.15.32 (2017-08-21):
- allow setting ``yaml.default_flow_style = None`` (default: ``False``) for
for ``typ='rt'``.
- fix for issue 149: multiplications on ``ScalarFloat`` now return ``float``
(reported by

0.15.31 (2017-08-15):
- fix Comment dumping

0.15.30 (2017-08-14):
- fix for issue with "compact JSON" not parsing: ``{"in":{},"out":{}}``
(reported on `StackOverflow <>`__ by
`mjalkio <>`_

0.15.29 (2017-08-14):
- fix issue #51: different indents for mappings and sequences (reported by
Alex Harvey)
- fix for flow sequence/mapping as element/value of block sequence with
sequence-indent minus dash-offset not equal two.

0.15.28 (2017-08-13):
- fix issue #61: merge of merge cannot be __repr__-ed (reported by Tal Liron)

0.15.27 (2017-08-13):
- fix issue 62, YAML 1.2 allows ``?`` and ``:`` in plain scalars if non-ambigious
(reported by nowox)
- fix lists within lists which would make comments disappear

0.15.26 (2017-08-10):
- fix for disappearing comment after empty flow sequence (reported by

0.15.25 (2017-08-09):
- fix for problem with dumping (unloaded) floats (reported by eyenseo)

0.15.24 (2017-08-09):
- added ScalarFloat which supports roundtripping of 23.1, 23.100,
42.00E+56, 0.0, -0.0 etc. while keeping the format. Underscores in mantissas
are not preserved/supported (yet, is anybody using that?).
- (finally) fixed longstanding issue 23 (reported by `Antony Sottile
<>`__), now handling comment between block
mapping key and value correctly
- warn on YAML 1.1 float input that is incorrect (triggered by invalid YAML
provided by Cecil Curry)
- allow setting of boolean representation (`false`, `true`) by using:
``yaml.boolean_representation = [u'False', u'True']``

0.15.23 (2017-08-01):
- fix for round_tripping integers on 2.7.X > sys.maxint (reported by ccatterina)

0.15.22 (2017-07-28):
- fix for round_tripping singe excl. mark tags doubling (reported and fix by Jan Brezina)

0.15.21 (2017-07-25):
- fix for writing unicode in new API, (reported on
`StackOverflow <>`__

0.15.20 (2017-07-23):
- wheels for windows including C extensions

0.15.19 (2017-07-13):
- added object constructor for rt, decorator ``yaml_object`` to replace YAMLObject.
- fix for problem using load_all with Path() instance
- fix for load_all in combination with zero indent block style literal
(``pure=True`` only!)

0.15.18 (2017-07-04):
- missing ``pure`` attribute on ``YAML`` useful for implementing `!include` tag
constructor for `including YAML files in a YAML file
- some documentation improvements
- trigger of doc build on new revision

0.15.17 (2017-07-03):
- support for Unicode supplementary Plane **output**
(input was already supported, triggered by
`this <>`__ Stack Overflow Q&A)

0.15.16 (2017-07-01):
- minor typing issues (reported and fix provided by
`Manvendra Singh <>`__
- small doc improvements

0.15.15 (2017-06-27):
- fix for issue 135, typ='safe' not dumping in Python 2.7
(reported by Andrzej Ostrowski <>`__)

0.15.14 (2017-06-25):
- fix for issue 133, in change ModuleNotFoundError to
ImportError (reported and fix by
`Asley Drake <>`__)

0.15.13 (2017-06-24):
- suppress duplicate key warning on mappings with merge keys (reported by
Cameron Sweeney)

0.15.12 (2017-06-24):
- remove fatal dependency of on wheel package (reported by
Cameron Sweeney)

0.15.11 (2017-06-24):
- fix for issue 130, regression in nested merge keys (reported by
`David Fee <>`__)

0.15.10 (2017-06-23):
- top level PreservedScalarString not indented if not explicitly asked to
- remove Makefile (not very useful anyway)
- some mypy additions

0.15.9 (2017-06-16):
- fix for issue 127: tagged scalars were always quoted and seperated
by a newline when in a block sequence (reported and largely fixed by
`Tommy Wang <>`__)

0.15.8 (2017-06-15):
- allow plug-in install via ``install ruamel.yaml[jinja2]``

0.15.7 (2017-06-14):
- add plug-in mechanism for load/dump pre resp. post-processing

0.15.6 (2017-06-10):
- a set() with duplicate elements now throws error in rt loading
- support for toplevel column zero literal/folded scalar in explicit documents

0.15.5 (2017-06-08):
- repeat `load()` on a single `YAML()` instance would fail.

0.15.4 (2017-06-08):
- `transform` parameter on dump that expects a function taking a
string and returning a string. This allows transformation of the output
before it is written to stream. This forces creation of the complete output in memory!
- some updates to the docs

0.15.3 (2017-06-07):
- No longer try to compile C extensions on Windows. Compilation can be forced by setting
the environment variable `RUAMEL_FORCE_EXT_BUILD` to some value
before starting the `pip install`.

0.15.2 (2017-06-07):
- update to conform to mypy 0.511: mypy --strict

0.15.1 (2017-06-07):
- `duplicate keys <>`__
in mappings generate an error (in the old API this change generates a warning until 0.16)
- dependecy on ruamel.ordereddict for 2.7 now via extras_require

0.15.0 (2017-06-04):
- it is now allowed to pass in a ``pathlib.Path`` as "stream" parameter to all
load/dump functions
- passing in a non-supported object (e.g. a string) as "stream" will result in a
much more meaningful YAMLStreamError.
- assigning a normal string value to an existing CommentedMap key or CommentedSeq
element will result in a value cast to the previous value's type if possible.
- added ``YAML`` class for new API

0.14.12 (2017-05-14):
- fix for issue 119, deepcopy not returning subclasses (reported and PR by
Constantine Evans <>)

0.14.11 (2017-05-01):
- fix for issue 103 allowing implicit documents after document end marker line (``...``)
in YAML 1.2

0.14.10 (2017-04-26):
- fix problem with emitting using cyaml

0.14.9 (2017-04-22):
- remove dependency on ``typing`` while still supporting ``mypy``
- fix unclarity in doc that stated 2.6 is supported (reported by feetdust)

0.14.8 (2017-04-19):
- fix Text not available on 3.5.0 and 3.5.1, now proactively setting version guards
on all files (reported by `João Paulo Magalhães <>`__)

0.14.7 (2017-04-18):
- round trip of integers (decimal, octal, hex, binary) now preserve
leading zero(s) padding and underscores. Underscores are presumed
to be at regular distances (i.e. ``0o12_345_67`` dumps back as
``0o1_23_45_67`` as the space from the last digit to the
underscore before that is the determining factor).

0.14.6 (2017-04-14):
- binary, octal and hex integers are now preserved by default. This
was a known deficiency. Working on this was prompted by the issue report (112)
from devnoname120, as well as the additional experience with `.replace()`
on `scalarstring` classes.
- fix issues 114: cannot install on Buildozer (reported by mixmastamyk).
Setting env. var ``RUAMEL_NO_PIP_INSTALL_CHECK`` will suppress ``pip``-check.

0.14.5 (2017-04-04):
- fix issue 109: None not dumping correctly at top level (reported by Andrea Censi)
- fix issue 110: .replace on Preserved/DoubleQuoted/SingleQuoted ScalarString
would give back "normal" string (reported by sandres23)

0.14.4 (2017-03-31):
- fix readme

0.14.3 (2017-03-31):
- fix for 0o52 not being a string in YAML 1.1 (reported on
`StackOverflow Q&A 43138503 <>`__ by
`Frank D <>`__)

0.14.2 (2017-03-23):
- fix for old default pip on Ubuntu 14.04 (reported by Sébastien Maccagnoni-Munch)

0.14.1 (2017-03-22):
- fix Text not available on 3.5.0 and 3.5.1 (reported by Charles Bouchard-Légaré)

0.14.0 (2017-03-21):
- updates for mypy --strict
- preparation for moving away from inheritance in Loader and Dumper, calls from e.g.
the Representer to the Serializer.serialize() are now done via the attribute
.serializer.serialize(). Usage of .serialize() outside of Serializer will be
deprecated soon
- some extra tests on functions


For older changes see the file

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