As a Python developer, encountering error messages is an inevitable part of the coding process. One such error, “AttributeError: module h11 has no attribute event,” can be particularly perplexing, especially for those unfamiliar with the h11 module. In this post, we’ll demystify this error by explaining the h11 module, its purpose, and how you can resolve this AttributeError in your Python projects.

Understanding the h11 Module

The h11 module is a pure-Python implementation of the HTTP/1.1 protocol, designed to create and parse HTTP messages simply and efficiently. This makes it suitable for use in web servers, proxies, and clients. One of the key benefits of h11 is its compatibility with both synchronous and asynchronous I/O frameworks, offering flexibility for developers.

Unlike high-level HTTP libraries such as Requests or urllib3, h11 focuses on providing a low-level API for handling the HTTP protocol. This makes it an ideal choice for developers building custom HTTP solutions or working with the protocol at a deeper level.

Identifying the Causes of the AttributeError

The “AttributeError: module h11 has no attribute event” error typically arises due to one of the following reasons:

  1. Incorrect import statement
  2. h11 version issue
  3. Misuse of the h11 API

Let’s examine each of these causes in more detail and explore how to resolve them.

Fixing Incorrect Import Statements

First, ensure that the h11 module is installed in your Python environment by running the following command:

pip install h11

Once the h11 module is installed, verify that your import statements are correct. The proper way to import the h11 module and its components is as follows:

import h11 from h11 import Connection, Request, Response

Make sure your import statements are accurate and avoid referencing any non-existent attributes or modules.

Updating the h11 Module

If the import statement is correct, the issue might be with the version of h11 you are using. The “event” attribute may be absent in outdated versions or incompatible with your code.

To check the h11 version installed in your Python environment, run the following command:

pip show h11

Compare the installed version with the latest release available on the h11 GitHub repository or PyPI (Python Package Index). If the installed version is outdated, update it with the following command:

pip install --upgrade h11

If the issue persists even after updating the h11 module, it might be due to API changes. Review the library’s documentation and release notes for any breaking changes that may affect your code.

Correctly Using the h11 API

If your import statements are correct and your h11 module is up-to-date, the issue might be with how you are using the h11 API. Ensure that you are using the API correctly and consult the library’s documentation for guidance.

The primary components of the h11 library are Connection, Request, and Response objects. The Connection object manages the state of an HTTP connection, while Request and Response objects represent HTTP requests and responses, respectively. Here’s an example of using the h11 API correctly:

# Create a client-side connection
conn = Connection(our_role=h11.CLIENT)

# Prepare a request
request = Request(method="GET", target="/", headers=[("Host", ""), ("User-Agent", "h11-example")])

# Send the request
request_data = conn.send(request)

# Receive the response
response_data = conn.receive_data()
response = conn.next_event()

# Check if the response is an h11.Response object
if isinstance(response, h11.Response):
    print("Received response:", response)
    print("Unexpected event:", response)

In this example, we create a Connection object in the client role, prepare an HTTP GET request, send the request, and receive the response. We then check if the received response is an h11.Response object. Notice that we do not use the “event” attribute directly, as it is not part of the h11 API.

If you still encounter the “AttributeError: module h11 has no attribute event” error, double-check your code and consult the h11 library’s documentation to ensure you are using the API correctly.


The “AttributeError: module h11 has no attribute event” error can be caused by several factors, such as incorrect import statements, an outdated or incompatible h11 module version, or misuse of the h11 API. By addressing these issues, you should be able to resolve this error and continue working on your Python projects that involve the HTTP/1.1 protocol.

Remember to always keep your dependencies up-to-date, check the library’s documentation, and follow best practices when using third-party libraries in your projects. This will help you avoid similar errors and ensure a smoother development experience.

Disclaimer: The code snippets and examples provided on this blog are for educational and informational purposes only. You are free to use, modify, and distribute the code as you see fit, but I make no warranties or guarantees regarding its accuracy or suitability for any specific purpose. By using the code from this blog, you agree that I will not be held responsible for any issues or damages that may arise from its use. Always exercise caution and thoroughly test any code in your own development environment before using it in a production setting.

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