PyPI Server Skill

This skill provides guidance for creating Python packages and serving them through a local PyPI server for installation via pip.

When to Use This Skill

This skill applies to tasks that involve:

• Creating Python packages with custom modules
• Building distributable packages (.tar.gz, .whl files)
• Setting up a local PyPI-compatible server
• Making packages installable via pip install --index-url

Environment Assessment (Critical First Step)

Before starting any work, assess the execution environment to avoid compatibility issues:

# Check Python version - critical for tool compatibility
python3 --version

# Check available package tools
which pip3 && pip3 --version
which uv 2>/dev/null  # Fast package manager alternative

# Check for process management tools
which pkill lsof fuser 2>/dev/null || echo "Limited process tools"

Key compatibility consideration: Python 3.13+ removed the cgi module, which breaks pypiserver. Plan for fallback approaches if using Python 3.13+.

Approach Selection

Option 1: Built-in HTTP Server (Recommended for Python 3.13+)

Use Python's built-in http.server module - no external dependencies, works across all Python versions.

Directory structure required:

server-root/
└── simple/
    └── packagename/
        ├── packagename-0.1.0.tar.gz
        └── packagename-0.1.0-py3-none-any.whl

Server command:

cd server-root && python3 -m http.server 8080

Option 2: pypiserver (Python < 3.13 only)

More feature-rich but has Python version constraints.

pip install pypiserver
pypi-server run -p 8080 ./packages/

Note: The command is pypi-server (with hyphen), not pypiserver.

Package Creation Workflow

Step 1: Create Package Structure

packagename/
├── pyproject.toml
├── src/
│   └── packagename/
│       └── __init__.py

Or flat layout:

packagename/
├── pyproject.toml
└── packagename/
    └── __init__.py

Step 2: Configure pyproject.toml

Minimal configuration:

[build-system]
requires = ["setuptools>=61.0", "wheel"]
build-backend = "setuptools.build_meta"

[project]
name = "packagename"
version = "0.1.0"
description = "Package description"
requires-python = ">=3.8"

Step 3: Build the Package

cd packagename
pip install build
python -m build

This creates dist/packagename-0.1.0.tar.gz and dist/packagename-0.1.0-py3-none-any.whl.

Server Setup Workflow

Step 1: Create Server Directory Structure

mkdir -p pypi-server/simple/packagename
cp packagename/dist/* pypi-server/simple/packagename/

Step 2: Start the Server

Important: Track the working directory from which the server starts. The server will only serve files relative to its starting directory.

cd pypi-server && python3 -m http.server 8080 &

Record the PID for later cleanup:

echo $! > server.pid

Step 3: Verify Server Accessibility

# Check root endpoint
curl -s http://localhost:8080/

# Check simple index (this is what pip uses)
curl -s http://localhost:8080/simple/

# Check package listing
curl -s http://localhost:8080/simple/packagename/

Verification Strategy

Test Package Installation

pip install --index-url http://localhost:8080/simple packagename==0.1.0

Test Package Functionality

import packagename
# Test the actual functionality

Full Verification Checklist

1. Server responds on root endpoint (/)
2. Server responds on /simple/ endpoint
3. Package files are listed at /simple/packagename/
4. pip install succeeds with explicit index URL
5. Installed package imports correctly
6. Package functionality works as expected

Process Management

Starting Background Servers

# Start with explicit working directory tracking
cd /path/to/server-root
python3 -m http.server 8080 &
SERVER_PID=$!
echo "Server PID: $SERVER_PID"

Checking Server Status

# Check if port is in use
python3 -c "import socket; s=socket.socket(); s.settimeout(1); result=s.connect_ex(('localhost', 8080)); print('Port in use' if result==0 else 'Port free'); s.close()"

# List processes on port (if tools available)
lsof -i :8080 2>/dev/null || fuser 8080/tcp 2>/dev/null

Stopping Servers

# If PID is known
kill $SERVER_PID

# If PID unknown, find and kill
pkill -f "http.server 8080" 2>/dev/null

# Fallback: use /proc filesystem
for pid in /proc/[0-9]*; do
    if grep -q "http.server" "$pid/cmdline" 2>/dev/null; then
        kill "$(basename $pid)" 2>/dev/null
    fi
done

Common Pitfalls and Solutions

Pitfall 1: Server Running from Wrong Directory

Symptom: Server running but /simple/ returns 404.

Cause: A previous server instance started from a different directory is still running.

Solution: Kill all HTTP server processes, verify port is free, then restart from the correct directory.

Pitfall 2: Port Already in Use

Symptom: "Address already in use" error when starting server.

Solution: Find and kill the process using the port, or use a different port.

Pitfall 3: pypiserver Fails on Python 3.13+

Symptom: Import error about missing cgi module.

Solution: Use the built-in http.server approach instead.

Pitfall 4: pip Can't Find Package

Symptom: pip install fails with "No matching distribution found."

Possible causes:

• Incorrect directory structure (must be /simple/packagename/)
• Server not running or wrong port
• Package files not copied to server directory
• Version mismatch in install command

Debug approach:

# Verify server response includes package files
curl http://localhost:8080/simple/packagename/

Pitfall 5: Package Installs but Import Fails

Symptom: pip install succeeds but import packagename fails.

Cause: Package structure issue - the importable name may differ from the package name.

Solution: Verify __init__.py exists and the package structure matches pyproject.toml configuration.

Clean State Management

Before starting server operations, ensure a clean state:

1. Kill any existing servers on the target port
2. Verify port is free
3. Remove stale server directories if recreating
4. Start fresh server with explicit directory

This prevents confusion from orphaned processes or stale state.