fastyaml-rs 0.6.1

A fast YAML parser and linter for Python, powered by Rust

fastyaml-rs

A fast YAML 1.2.2 parser and linter for Python, powered by Rust.

[!IMPORTANT] Requires Python 3.10 or later.

Installation

pip install fastyaml-rs

Usage

import fast_yaml

# Parse YAML
data = fast_yaml.safe_load("name: test\nvalue: 123")
print(data)  # {'name': 'test', 'value': 123}

# Dump YAML
yaml_str = fast_yaml.safe_dump({"name": "test", "value": 123})
print(yaml_str)  # name: test\nvalue: 123\n

Features

• YAML 1.2.2 compliant — Full Core Schema support
• Fast — 5-10x faster than PyYAML
• PyYAML compatible — Drop-in replacement with load, dump, Loader, Dumper classes
• Linter — Rich diagnostics with line/column tracking
• Parallel processing — Multi-threaded parsing for large files
• Batch processing — Process multiple files in parallel
• Type stubs — Full IDE support with .pyi files

Batch Processing

Process multiple YAML files in parallel:

from fast_yaml._core import batch

# Parse multiple files
result = batch.process_files([
    "config1.yaml",
    "config2.yaml",
    "config3.yaml",
])
print(f"Processed {result.total} files, {result.failed} failed")

# With configuration
config = batch.BatchConfig(workers=4, indent=2)
result = batch.process_files(paths, config)

Format Files

# Dry-run: get formatted content without writing
results = batch.format_files(["config.yaml"])
for path, content, error in results:
    if content:
        print(f"{path}: {len(content)} bytes")

# In-place: format and write back
result = batch.format_files_in_place(["config.yaml"])
print(f"Changed {result.changed} files")

BatchConfig Options

Option	Default	Description
workers	Auto	Number of worker threads
mmap_threshold	512 KB	Mmap threshold for large files
max_input_size	100 MB	Maximum file size
indent	2	Indentation width
width	80	Line width
sort_keys	False	Sort dictionary keys

BatchResult

result = batch.process_files(paths)
print(f"Total: {result.total}")
print(f"Success: {result.success}")
print(f"Changed: {result.changed}")
print(f"Failed: {result.failed}")
print(f"Duration: {result.duration_ms}ms")
print(f"Files/sec: {result.files_per_second()}")

for path, error in result.errors():
    print(f"Error in {path}: {error}")

Documentation

See the main repository for full documentation.

License

Licensed under either of Apache License, Version 2.0 or MIT License at your option.