A set of performance guidelines for Python 3.11 and newer, covering how programs handle input and output, data, memory, concurrency, loops, strings, and function calls. Python is a programming language commonly used for web services, scripts, and data work.

Use it when creating, reviewing, or refactoring Python code involving asynchronous work, data structures, memory use, parallel tasks, loops, strings, or common Python idioms.

It helps identify code that uses more time or memory than necessary, especially in data-heavy or concurrent programs. The advice gives agents consistent patterns to follow when writing or changing Python code.

python — Skill by pproenca

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods

npx agentmods add skills/pproenca/dot-skills/python

Any agent

npx skills add pproenca/dot-skills --skill python

Clone the repo

git clone --depth 1 https://github.com/pproenca/dot-skills

Made for: Claude Code, Codex.

Per session 62 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 2,290 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 0 findings. Scan, not verified.

Origin original No closer match found in the catalogue.

Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

Model	Per session	Once invoked
Fable 5	$0.00062	$0.02290
Opus 5	$0.00031	$0.01145
Sonnet 5	$0.00012	$0.00458
Haiku 4.5	$0.00006	$0.00229

Measured yesterday against content hash 3edd3aec6633, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

python scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured yesterday.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

skills/.curated/python/SKILL.md · 104 lines

How it starts

The opening of the file, as written. The whole thing — 104 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Python 3.11 Best Practices

Comprehensive performance optimization guide for Python 3.11+ applications. Contains 42 rules across 8 categories, prioritized by impact to guide automated refactoring and code generation.

When to Apply

Reference these guidelines when:

Writing new Python async I/O code
Choosing data structures for collections
Optimizing memory usage in data-intensive applications
Implementing concurrent or parallel processing
Reviewing Python code for performance issues

Rule Categories by Priority

Priority	Category	Impact	Prefix
1	I/O & Async Patterns	CRITICAL	`io-`
2	Data Structure Selection	CRITICAL	`ds-`
3	Memory Optimization	HIGH	`mem-`
4	Concurrency & Parallelism	HIGH	`conc-`
5	Loop & Iteration	MEDIUM	`loop-`
6	String Operations	MEDIUM	`str-`
7	Function & Call Overhead	LOW-MEDIUM	`func-`
8	Python Idioms & Micro	LOW	`py-`

I/O & Async Patterns — CRITICAL
- 1.1 Defer await Until Value Needed — CRITICAL (2-5× faster for dependent operations)
- 1.2 Use aiofiles for Async File Operations — CRITICAL (prevents event loop blocking)
- 1.3 Use asyncio.gather() for Concurrent I/O — CRITICAL (2-10× throughput improvement)
- 1.4 Use Connection Pooling for Database Access — CRITICAL (100-200ms saved per connection)
- 1.5 Use Semaphores to Limit Concurrent Operations — CRITICAL (prevents resource exhaustion)
- 1.6 Use uvloop for Faster Event Loop — CRITICAL (2-4× faster async I/O)
Data Structure Selection — CRITICAL
- 2.1 Use bisect for O(log n) Sorted List Operations — CRITICAL (O(n) to O(log n) search)
- 2.2 Use defaultdict to Avoid Key Existence Checks — CRITICAL (eliminates redundant lookups)
- 2.3 Use deque for O(1) Queue Operations — CRITICAL (O(n) to O(1) for popleft)
- 2.4 Use Dict for O(1) Key-Value Lookup — CRITICAL (O(n) to O(1) lookup)
- 2.5 Use frozenset for Hashable Set Keys — CRITICAL (enables set-of-sets patterns)
- 2.6 Use Set for O(1) Membership Testing — CRITICAL (O(n) to O(1) lookup)

Read the full file on GitHub · 104 lines

Files

What ships with it

46 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

yesterday First seen · 104 lines · 62 tokens per session scan A 3edd3aec6633

Subscribe to this mod's changes

python is a skill published in the GitHub repository pproenca/dot-skills (200 stars, last pushed 16d ago), licensed MIT. It adds 62 tokens to every session and 2,290 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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python