Basic Usage

Load and dump

You load a YAML document using:

from ruamel.yaml import YAML

yaml=YAML(typ='safe')   # default, if not specfied, is 'rt' (round-trip)

in this doc can be a file pointer (i.e. an object that has the .read() method, a string or a pathlib.Path(). typ='safe' accomplishes the same as what safe_load() did before: loading of a document without resolving unknown tags. Provide pure=True to enforce using the pure Python implementation, otherwise the faster C libraries will be used when possible/available but these behave slightly different (and sometimes more like a YAML 1.1 loader).

Dumping works in the same way:

from ruamel.yaml import YAML

yaml.default_flow_style = False
yaml.dump({'a': [1, 2]}, s)

in this s can be a file pointer (i.e. an object that has the .write() method, or a pathlib.Path(). If you want to display your output, just stream to sys.stdout.

If you need to transform a string representation of the output provide a function that takes a string as input and returns one:

def tr(s):
    return s.replace('\n', '<\n')  # such output is not valid YAML!

yaml.dump(data, sys.stdout, transform=tr)

More examples

Using the C based SafeLoader (at this time is inherited from libyaml/PyYAML and e.g. loads 0o52 as well as 052 as integer 42):

from ruamel.yaml import YAML

yaml.load("""a:\n  b: 2\n  c: 3\n""")

Using the Python based SafeLoader (YAML 1.2 support, 052 loads as 52):

from ruamel.yaml import YAML

yaml=YAML(typ="safe", pure=True)
yaml.load("""a:\n  b: 2\n  c: 3\n""")

Restrictions when using the C based SafeLoader/SafeDumper:

  • yaml.indent will set the same value for mappings and sequences. (Issue 471)