Miscellaneous#

Why do I get the error: module 'websockets' has no attribute '...'?#

Often, this is because you created a script called websockets.py in your current working directory. Then import websockets imports this module instead of the websockets library.

Why does my IDE fail to show documentation for websockets APIs?#

You are probably using the convenience imports e.g.:

import websockets

websockets.connect(...)
websockets.serve(...)

This is incompatible with static code analysis. It may break auto-completion and contextual documentation in IDEs, type checking with mypy, etc.

Instead, use the real import paths e.g.:

import websockets.client
import websockets.server

websockets.client.connect(...)
websockets.server.serve(...)

Why is the default implementation located in websockets.legacy?#

This is an artifact of websockets’ history. For its first eight years, only the asyncio implementation existed. Then, the Sans-I/O implementation was added. Moving the code in a legacy submodule eased this refactoring and optimized maintainability.

All public APIs were kept at their original locations. websockets.legacy isn’t a public API. It’s only visible in the source code and in stack traces. There is no intent to deprecate this implementation — at least until a superior alternative exists.

Why is websockets slower than another library in my benchmark?#

Not all libraries are as feature-complete as websockets. For a fair benchmark, you should disable features that the other library doesn’t provide. Typically, you may need to disable:

  • Compression: set compression=None

  • Keepalive: set ping_interval=None

  • UTF-8 decoding: send bytes rather than str

If websockets is still slower than another Python library, please file a bug.

Are there onopen, onmessage, onerror, and onclose callbacks?#

No, there aren’t.

websockets provides high-level, coroutine-based APIs. Compared to callbacks, coroutines make it easier to manage control flow in concurrent code.

If you prefer callback-based APIs, you should use another library.