pydanticio 0.4.0

A Tiny file IO utility library for Python powered by Pydantic

A tiny file IO utility library for Python powered by Pydantic. This library is a port of the Rust library SerdeIO.

Features

• Type-safe: Read and write Pydantic models with full type inference
• Format support: CSV, JSON, JSON Lines, TOML, YAML, and MessagePack (optional)
• Auto-detection: Automatically detects format from file extension
• Simple API: Intuitive functions for single records and lists
• Zero dependencies: Core library only requires Pydantic

Installation

# Standard distribution
pip install pydanticio

# With YAML support
pip install pydanticio[yaml]

# With MessagePack support
pip install pydanticio[messagepack]

# With TOML support
pip install pydanticio[toml]

Quick Start

from pydantic import BaseModel
from pydanticio import read_records_from_file, write_records_to_file

class User(BaseModel):
    name: str
    age: int

# Read from any supported format (auto-detected from extension)
users = read_records_from_file("users.csv", User)

# Or specify format explicitly (overrides file extension)
users = read_records_from_file("data.txt", User, data_format="csv")

# Write to any supported format
write_records_to_file("output.json", users)

Supported Formats

Format	File Extensions	Single Record	List of Records
CSV	.csv	No	Yes
JSON	.json	Yes	Yes
JSON Lines	.jsonl, .jl, .jsl, .json_lines	No	Yes
MessagePack	.msgpack	Yes	Yes
TOML	.toml	Yes	No
YAML	.yaml, .yml	Yes	Yes

All text-based formats use UTF-8 encoding.

Newline Handling

All text-based formats handle newlines automatically:

• On read: Any newline style (\n, \r\n, or \r) is accepted and normalized
• On write: Each format uses its appropriate line ending per specification

Format	Line Ending	Notes
CSV	\r\n	RFC 4180
JSON	\n
JSON Lines	\n	RFC 7464
TOML	Platform
YAML	\n

API Reference

Reading

Function	Description	Supported Formats
read_record_from_reader(reader, model, format)	Read single record from BinaryIO	JSON, MessagePack, TOML, YAML
read_record_from_file(path, model, data_format=None)	Read single record from file path	JSON, MessagePack, TOML, YAML
read_records_from_reader(reader, model, format)	Read list of records from BinaryIO	All formats except for TOML
read_records_from_file(path, model, data_format=None)	Read list of records from file path	All formats except for TOML

Writing

Function	Description	Supported Formats
write_record_to_writer(writer, record, format)	Write single record to BinaryIO	JSON, MessagePack, TOML, YAML
write_record_to_file(path, record, data_format=None)	Write single record to file path	JSON, MessagePack, TOML, YAML
write_records_to_writer(writer, records, format)	Write list of records to BinaryIO	All formats except for TOML
write_records_to_file(path, records, data_format=None)	Write list of records to file path	All formats except for TOML

Format Specification

When using *_from_file or *_to_file functions, you can optionally specify the data format explicitly using the data_format parameter. If not specified, the format is automatically detected from the file extension.

from pydanticio import read_records_from_file, write_records_to_file

# Auto-detects CSV format from .csv extension
users = read_records_from_file("data/users.csv", User)

# Explicit format overrides file extension
users = read_records_from_file("data/file.xyz", User, data_format="csv")
write_records_to_file("data/output.txt", users, data_format="json")

Valid format values:

Value	Description
"json"	JSON format
"yaml"	YAML format
"messagepack"	MessagePack
"toml"	TOML format (single record only)
"csv"	CSV format (records only)
"json_lines"	JSON Lines format (records only)

When data_format is None (default), the format is automatically detected from the file extension. When explicitly specified, it overrides the automatic detection.

Explicit Format Specification

Use the data_format parameter to override automatic format detection from file extensions:

from pydantic import BaseModel
from pydanticio import (
    read_records_from_file,
    write_records_to_file,
    read_record_from_file,
    write_record_to_file,
)

class User(BaseModel):
    name: str
    age: int

# Override file extension - read CSV from .txt file
users = read_records_from_file("data/users.txt", User, data_format="csv")

# Write JSON to file with non-standard extension
write_records_to_file("data/export.xyz", users, data_format="json")

# Single record with explicit format
class Config(BaseModel):
    setting: str
    value: int

config = read_record_from_file("config.data", Config, data_format="yaml")
write_record_to_file("config.out", config, data_format="toml")

This is useful when:

• Working with files that have non-standard extensions
• Converting between formats while preserving original file
• Ensuring consistent format regardless of file naming

Examples

Reading and Writing Lists

from pydantic import BaseModel
from pydanticio import read_records_from_file, write_records_to_file

class User(BaseModel):
    name: str
    age: int

# Convert between formats
users = read_records_from_file("users.csv", User)
write_records_to_file("users.json", users)

Reading Single Records

from pydantic import BaseModel
from pydanticio import read_record_from_file

class Config(BaseModel):
    name: str
    version: int
    enabled: bool

config = read_record_from_file("config.toml", Config)
print(config.name, config.version)

Using Streams

from pydantic import BaseModel
from pydanticio import read_records_from_reader, write_records_to_writer

class Item(BaseModel):
    id: int
    value: str

# Read from a file stream
with open("data.json", "rb") as f:
    items = read_records_from_reader(f, Item)

# Write to a BytesIO stream
from io import BytesIO
buffer = BytesIO()
write_records_to_writer(buffer, items, "json")

Converting Between Formats

# Command line usage example
python examples/convert_format.py input.csv output.json

See examples/convert_format.py for the full source code.

Requirements

• Python 3.12+
• Pydantic 2.5.0+

License

MIT License