func_args 1.0.0

A lightweight Python library for creating wrapper functions with enhanced argument handling using sentinel values to mark parameters as required or optional.

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Welcome to func_args Documentation

Overview

func_args is a lightweight Python library for creating wrapper functions with enhanced argument handling. It solves common problems when working with third-party APIs that have suboptimal interface designs.

The library provides sentinel values (REQ and OPT) that can be used as function parameter defaults to:

• Mark parameters as required

• Mark parameters as optional and easily exclude them from kwargs

Additionally, func_args includes dataclasses enhancements for parameter validation and conversion.

Design Philosophy

func_args follows these core principles:

1. Explicit over implicit - Parameters are clearly marked as required or optional

2. Fail fast - Required parameters are validated early

3. Minimal overhead - Simple API with minimal processing cost

4. Flexible integration - Works with any Python function without modifying the original

5. Type hint support - Full support for Python type annotations

6. Consistent error handling - Clear error messages for missing required parameters

The library solves several common problems:

• Creating wrapper functions around third-party APIs with poor parameter interfaces

• Building flexible functions with many optional parameters

• Enforcing required parameters without complex conditional logic

• Removing optional parameters from kwargs dictionaries to avoid passing unused parameters

Usage Examples

Basic Sentinels

In this example, we create a wrapper around an AWS S3 put_object API:

def put_object(
    Bucket: str,
    Key: str,
    Body: bytes,
    Metadata: T.Optional[dict[str, str]] = ...,
    Tags: T.Optional[dict[str, str]] = ...,
):
    ...

from func_args.api import REQ, OPT, prepare_kwargs

# Our enhanced wrapper with REQ and OPT
def better_put_object(
    Bucket: str = REQ,
    Key: str = REQ,
    Body: bytes = REQ,
    Metadata: T.Optional[dict[str, str]] = OPT,
    Tags: T.Optional[dict[str, str]] = OPT,
):
    # custom parameter handling
    if Metadata is NA:
        Metadata = {"creator": "admin"}
    if Tags is NA:
        Tags = {"creator": "admin"}

    # Prepare kwargs with validation
    kwargs = dict(
        Bucket=Bucket,
        Key=Key,
        Body=Body,
        Metadata=Metadata,
        Tags=Tags,
    )

    # This will:
    # 1. Raise ParamError if any REQ values remain
    # 2. Remove any OPT values
    # 3. Return a clean dict with only provided values
    cleaned_kwargs = prepare_kwargs(kwargs)

    # Call the original API with only the necessary parameters
    return put_object(**cleaned_kwargs)

Required Parameter Validation

from func_args.arg import REQ, check_required

# Function with required parameters
def create_user(username=REQ, email=REQ, role="user"):
    # Validate required parameters
    check_required(username=username, email=email)

    # If we got here, all required parameters were provided
    return {"username": username, "email": email, "role": role}

# This works
user = create_user(username="alice", email="[e-mail]")

# This raises ParamError: "Missing required argument: 'email'"
try:
    user = create_user(username="bob")
except ParamError as e:
    print(e)

Optional Parameter Removal

from func_args.arg import OPT, remove_optional

# Function with many optional parameters
def search_items(query, limit=10, offset=0, sort_by=OPT, filter_by=OPT, include_deleted=False):
    # Build base query parameters
    params = {
        "query": query,
        "limit": limit,
        "offset": offset,
        "sort_by": sort_by,
        "filter_by": filter_by,
        "include_deleted": include_deleted,
    }

    # Remove optional parameters that weren't provided
    clean_params = remove_optional(**params)

    # Now we can safely pass to the API without sending None values or defaults
    return api_search(**clean_params)

Enhanced Dataclasses

import dataclasses
from func_args.dataclass import BaseModel, REQ, OPT

@dataclasses.dataclass
class UserParameters(BaseModel):
    """Parameter class for user operations with validation."""

    # Required fields
    username: str = dataclasses.field(default=REQ)
    email: str = dataclasses.field(default=REQ)

    # Optional fields
    display_name: str = dataclasses.field(default=OPT)
    role: str = dataclasses.field(default="user")
    tags: list = dataclasses.field(default_factory=list)

    def validate_email(self):
        """Additional validation logic."""
        if not "@" in self.email:
            raise ValueError("Invalid email format")

    def __post_init__(self):
        # Call the base class validation
        super().__post_init__()
        # Perform additional validation
        self.validate_email()

# Usage
params = UserParameters(username="alice", email="[e-mail]")

# Convert to dict with all fields (including OPT sentinel values)
full_dict = params.to_dict()
# {"username": "alice", "email": "[e-mail]", "display_name": OPT, "role": "user", "tags": []}

# Convert to dict with only provided values (excluding OPT sentinels)
kwargs = params.to_kwargs()
# {"username": "alice", "email": "[e-mail]", "role": "user", "tags": []}

Install

func_args is released on PyPI, so all you need is to:

$ pip install func-args

To upgrade to latest version:

$ pip install --upgrade func-args