YAML in Python with PyYAML and ruamel
Load, validate, and write YAML in Python — with safe loading, schema validation, and round-trip.
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Tags: YAML Python PyYAML, Python yaml.safe_load, ruamel yaml Python
YAML in Python with PyYAML and ruamel PyYAML and ruamel.yaml are the two main libraries for YAML processing in Python. PyYAML is the standard choice for reading and writing; ruamel.yaml is the choice when comments and formatting must survive round-trips. The YAML 1.2 specification is the authoritative standard, and the PyYAML documentation covers all supported loading modes including . --- Installing PyYAML PyYAML is already installed in many environments. Check with . Reading YAML with safeload Safe Load vs Unsafe Load Writing YAML with yaml.dump Type Handling YAML to Python type mapping with PyYAML: | YAML | Python type | |------|------------| | / | | | | | | | | | / | | | | | | | | | | | | | | | | | Beware of YAML 1.1 coercion in PyYAML — , , , become booleans: Loading Multiple…
Frequently Asked Questions
How do I read YAML in Python?
Install PyYAML with `pip install pyyaml` and use `yaml.safe_load(open('config.yaml'))`. `safe_load` is secure for untrusted input; it loads only basic Python types (dict, list, str, int, float, bool, None). Never use `yaml.load()` without an explicit Loader.
What is yaml.safe_load vs yaml.load?
`yaml.safe_load` only constructs basic Python objects (dict, list, str, int, float, bool, None, datetime). `yaml.load` without an explicit Loader could execute arbitrary Python code via `!!python/object` tags in malicious YAML. Always use `safe_load` for untrusted or user-supplied YAML.
How do I write YAML with comments in Python?
PyYAML does not preserve comments — it serializes the Python data structure without any comment information. For comment-preserving round-trips, use ruamel.yaml: `from ruamel.yaml import YAML; yaml = YAML(); yaml.preserve_quotes = True`. Comments in the source file are preserved when writing back.
What is ruamel.yaml for round-trip parsing?
ruamel.yaml is a fork of PyYAML that adds a round-trip parser/emitter preserving comments, quote styles, and ordering. Use it when you need to read a YAML file, modify some values, and write it back without destroying the original formatting.
How do I validate YAML against a schema in Python?
Load the YAML with yaml.safe_load to get a Python dict, then validate with jsonschema.validate(data, schema). Alternatively use pydantic to define the expected structure as a model and parse with YourModel(**data). Both approaches give you structured validation errors.
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