aiofiles
Async file operations for asyncio Python — provides async equivalents of open(), read(), write(), readline() that run file I/O in a thread pool without blocking the event loop. aiofiles features: aiofiles.open() async context manager with same interface as builtin open(), async read()/write()/readline()/readlines(), async iteration (async for line in file:), text and binary modes, tempfile support via aiofiles.tempfile, and os module equivalents (aiofiles.os.rename/remove/mkdir/stat/listdir).
Score Breakdown
⚙ Agent Friendliness
🔒 Security
File I/O library. Validate file paths to prevent directory traversal: Path(base_dir) / user_path; resolve() + is_relative_to(base_dir). File permissions: same as builtin open(). Do not write secrets to unprotected files.
⚡ Reliability
Best When
FastAPI, Starlette, or asyncio applications needing file I/O without blocking the event loop — aiofiles is the standard solution for async file operations in Python.
Avoid When
Synchronous code (use builtin open()), high-performance file I/O needing true async kernel support, or when file operations are truly negligible.
Use Cases
- • Agent async file read — import aiofiles; async def load_config(): async with aiofiles.open('config.json', 'r') as f: content = await f.read(); return json.loads(content) — async read; agent reads file without blocking asyncio event loop; critical in FastAPI/asyncio context where blocking I/O stalls all requests
- • Agent async file write — async def save_result(data, path): async with aiofiles.open(path, 'w') as f: await f.write(json.dumps(data, indent=2)) — async write; agent writes results to file asynchronously; file flush/close handled by context manager exit
- • Agent line-by-line processing — async with aiofiles.open('large.csv', 'r') as f: async for line in f: await process_line(line.strip()) — streaming; agent processes large files line by line without memory accumulation; async for on aiofiles file object; same interface as sync iteration
- • Agent binary file handling — async with aiofiles.open('image.png', 'rb') as f: image_bytes = await f.read(); await upload(image_bytes); async with aiofiles.open('output.pdf', 'wb') as f: await f.write(pdf_bytes) — binary; agent reads/writes binary files in async context
- • Agent async os operations — import aiofiles.os; await aiofiles.os.rename('temp.txt', 'final.txt'); await aiofiles.os.makedirs('output/subdir', exist_ok=True); stat = await aiofiles.os.stat('file.txt'); files = await aiofiles.os.listdir('.') — async os; agent performs file system operations without blocking event loop
Not For
- • Synchronous code — aiofiles requires async/await; for sync file I/O use builtin open()
- • High-performance file I/O — aiofiles uses thread pool delegation; for true async file I/O use io_uring (Linux) via dedicated library
- • Network file systems — aiofiles thread pool works but NFS/SMB latency still blocks threads; set appropriate thread pool size
Interface
Authentication
No auth — file I/O library.
Pricing
aiofiles is Apache 2.0 licensed. Free for all use.
Agent Metadata
Known Gotchas
- ⚠ Must await all file operations — async with aiofiles.open('f', 'r') as f: content = f.read() — WRONG missing await; must be: content = await f.read(); all file operations (read, write, readline, flush, seek) must be awaited; forgetting await returns coroutine object not data
- ⚠ Context manager required for proper close — async with aiofiles.open('file', 'w') as f: await f.write(data) — context manager handles close on exit; without context manager: f = await aiofiles.open(...); try: ... finally: await f.close() — explicit close required; unclosed file: ResourceWarning
- ⚠ seek() and tell() are available but less common — await f.seek(0) to reset position; await f.tell() for current position; used for reading file multiple times or random access; agent code reading entire file: use read() without seek; for streaming: sequential reads without seek
- ⚠ async for line in file works — async with aiofiles.open('f', 'r') as f: async for line in f: process(line) — async iteration works; line includes trailing newline; use line.rstrip('\n') or line.strip(); readlines() returns list; readline() returns one line including newline
- ⚠ aiofiles.os vs os — aiofiles.os.rename() returns coroutine (must await); os.rename() is synchronous (do not call from async context without thread pool); agent code: replace os.* calls with await aiofiles.os.* in async functions; not all os functions have async equivalents — check docs; stat/remove/rename/makedirs/listdir available
- ⚠ Thread pool size limits concurrent file ops — aiofiles uses asyncio thread pool (default: min(32, os.cpu_count()+4) threads); many concurrent file operations may exhaust thread pool; agent code with many parallel file ops: limit concurrency: asyncio.Semaphore(10) for max 10 concurrent opens; or increase thread pool via loop.set_default_executor()
Full Evaluation Report
Detailed scoring breakdown, competitive positioning, security analysis, and improvement recommendations for aiofiles.
Scores are editorial opinions as of 2026-03-06.