Yamale

6.1.0 · active · verified Thu Apr 09

Yamale (ya·ma·lē) is a schema and validator for YAML. It allows for defining schemas in YAML files and validating other YAML data against them, supporting a wide range of data types and custom validators. The current version is 6.1.0, and it generally follows a regular release cadence with several minor and major releases each year.

Warnings

breaking In version 6.0.0, the command-line interface (CLI) was updated to strictly enforce that all paths provided to CLI arguments must exist. Previously, non-existent paths might have been silently ignored or handled differently.
Fix: Ensure all file and directory paths passed to the `yamale` CLI command are valid and exist before execution.
breaking Version 5.0.0 dropped support for Python versions older than 3.8. Running Yamale on Python 3.7 or earlier will result in errors.
Fix: Upgrade your Python environment to version 3.8 or newer to use Yamale v5.0.0 and above. The latest release supports Python 3.8+ up to 3.14.
gotcha Yamale schemas should always originate from trusted sources. The library does not inherently protect against intentionally malicious schemas, which could potentially lead to arbitrary code execution if an attacker controls the schema file. (A specific code injection vulnerability, CVE-2021-38305, was addressed in v3.0.8).
Fix: Only use schema files from known, trusted sources. Never use schemas provided by untrusted users directly. If schemas must be user-provided, implement strict sanitization and validation on the schema content itself before passing it to Yamale.
gotcha By default, Yamale operates in 'strict' mode. This means that if the data being validated contains elements (keys in a map, or items in a list) that are not explicitly defined in the schema, validation will fail. This can be unexpected if you want to allow extra data.
Fix: To allow extra, unspecified elements in your data without causing validation errors, you can disable strict mode. Use the `--no-strict` flag with the CLI or pass `strict=False` to the `yamale.validate()` function when using the API. You can also apply strict mode selectively to includes.

Install

pip install yamale Standard Installation
pip install yamale[ruamel] Installation with ruamel.yaml (for YAML 1.2 support)

Imports

yamale
```
import yamale
```
Main library import for schema and data handling.
make_schema
```
yamale.make_schema('./schema.yaml')
```
Used to load and parse a schema file.
make_data
```
yamale.make_data('./data.yaml')
```
Used to load and parse a data file for validation.
validate
```
yamale.validate(schema, data)
```
The primary function to validate data against a schema. Throws ValueError on invalid data.

Quickstart

This quickstart demonstrates how to define a simple YAML schema and then validate a YAML data file against it using Yamale's API. It creates temporary schema and data files, performs validation, and prints the result.

import yamale
import os

# Create dummy schema.yaml and data.yaml files for demonstration
# In a real scenario, these would be pre-existing files.
with open('schema.yaml', 'w') as f:
    f.write('name: str()\nage: int(max=200)\nawesome: bool()')

with open('data.yaml', 'w') as f:
    f.write('name: Bill\nage: 26\nawesome: True')

try:
    # Import Yamale and make a schema object:
    schema = yamale.make_schema('./schema.yaml')

    # Create a Data object
    data = yamale.make_data('./data.yaml')

    # Validate data against the schema. Throws a ValueError if data is invalid.
    yamale.validate(schema, data)
    print('Validation success! Data is valid against the schema.')

except ValueError as e:
    print(f'Validation failed!\n{e}')
except FileNotFoundError as e:
    print(f'Error: {e}. Ensure schema.yaml and data.yaml exist.')
finally:
    # Clean up dummy files
    if os.path.exists('schema.yaml'):
        os.remove('schema.yaml')
    if os.path.exists('data.yaml'):
        os.remove('data.yaml')

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