# Designing Python Apis

> Designs intuitive Python library APIs following principles of simplicity, consistency, and discoverability. Handles API evolution, deprecation, breaking changes, and error handling. Use when designing new library APIs, reviewing existing APIs for improvements, or managing API versioning and deprecations.

- **Type:** Skill
- **Install:** `agentstack add skill-wdm0006-python-skills-api-design`
- **Verified:** Yes — security-reviewed for prompt injection and unsafe behavior
- **Seller:** [wdm0006](https://agentstack.voostack.com/s/wdm0006)
- **Installs:** 0
- **Category:** [Agent Skills](https://agentstack.voostack.com/c/agent-skills)
- **Latest version:** 0.1.0
- **License:** MIT
- **Upstream author:** [wdm0006](https://github.com/wdm0006)
- **Source:** https://github.com/wdm0006/python-skills/tree/main/skills/api-design

## Install

```sh
agentstack add skill-wdm0006-python-skills-api-design
```

Requires the [AgentStack CLI](https://agentstack.voostack.com/docs/cli). Works with Claude Code, Cursor, and any MCP-compatible agent.

## About

# Python API Design

## Core Principles

1. **Simplicity**: Simple things simple, complex things possible
2. **Consistency**: Similar operations work similarly
3. **Least Surprise**: Behave as users expect
4. **Discoverability**: Find via autocomplete and help

## Progressive Disclosure Pattern

```python
# Level 1: Simple functions
from mylib import encode, decode
result = encode(37.7749, -122.4194)

# Level 2: Configurable classes
from mylib import Encoder
encoder = Encoder(precision=15)

# Level 3: Low-level access
from mylib.internals import BitEncoder
```

## Naming Conventions

```python
# Actions: verbs
encode(), decode(), validate()

# Retrieval: get_*
get_user(), get_config()

# Boolean: is_*, has_*, can_*
is_valid(), has_permission()

# Conversion: to_*, from_*
to_dict(), from_json()
```

## Error Handling

```python
class MyLibError(Exception):
    """Base exception with helpful messages."""
    def __init__(self, message: str, *, hint: str = None):
        super().__init__(message)
        self.hint = hint

# Usage
raise ValidationError(
    f"Latitude must be -90 to 90, got {lat}",
    hint="Did you swap latitude and longitude?"
)
```

## Deprecation

```python
import warnings

def old_function():
    warnings.warn(
        "old_function() deprecated, use new_function()",
        DeprecationWarning,
        stacklevel=2,
    )
    return new_function()
```

## Anti-Patterns

```python
# Bad: Boolean trap
process(data, True, False, True)

# Good: Keyword arguments
process(data, validate=True, cache=False)

# Bad: Mutable default
def process(items: list = []):

# Good: None default
def process(items: list | None = None):
```

For detailed patterns, see:
- **[PATTERNS.md](PATTERNS.md)** - Builder, factory, and advanced patterns
- **[EVOLUTION.md](EVOLUTION.md)** - API versioning and migration guides

## Review Checklist

```
Naming:
- [ ] Clear, self-documenting names
- [ ] Consistent patterns throughout
- [ ] Boolean params read naturally

Parameters:
- [ ] Minimal required parameters
- [ ] Sensible defaults
- [ ] Keyword-only after positional clarity

Errors:
- [ ] Custom exceptions with context
- [ ] Helpful error messages
- [ ] Documented in docstrings
```

## Learn More

This skill is based on the [Ergonomics](https://mcginniscommawill.com/guides/python-library-development/#ergonomics-the-joy-of-good-design) section of the [Guide to Developing High-Quality Python Libraries](https://mcginniscommawill.com/guides/python-library-development/) by [Will McGinnis](https://mcginniscommawill.com/). See these posts for deeper coverage:

- [The Art of API Design](https://mcginniscommawill.com/posts/2025-02-03-art-of-api-design/)
- [Designing for Developer Joy](https://mcginniscommawill.com/posts/2025-02-06-designing-for-developer-joy/)

## Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

- **Author:** [wdm0006](https://github.com/wdm0006)
- **Source:** [wdm0006/python-skills](https://github.com/wdm0006/python-skills)
- **License:** MIT

Install and usage instructions live in the source repository linked above.

## Pricing

- **Free** — Free

## Security capabilities

Automated source analysis of v0.1.0 — what this tool can access:

- **Network access:** no
- **Filesystem access:** no
- **Shell / process execution:** no
- **Environment & secrets:** no
- **Dynamic code execution:** no

*"Yes" means the capability is present in the source — more access means more to trust, not that it is unsafe.*


## Versions

- **0.1.0** — security scan: passed — Imported from the upstream source.

## Links

- Listing page: https://agentstack.voostack.com/l/skill-wdm0006-python-skills-api-design
- Seller: https://agentstack.voostack.com/s/wdm0006
- Browse the marketplace: https://agentstack.voostack.com/browse

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Listed on AgentStack — the marketplace for AI agent skills and MCP servers. Every listing is security-reviewed. Creators keep 70%.