How Can I Reload Python Modules to Upgrade Services Without Server Restarts?

Reloading Python Modules for Seamless Service Upgrades

In a long-running Python server, upgrading services without restarting the server can be crucial. This article explores how to achieve this by reloading Python modules.

Unloading a Module

The question arises: how do you unload (and then reload) a Python module? This is where importlib.reload() comes into play.

Using importlib.reload()

1. Import importlib: from importlib import reload
2. Reload the module: foo = reload(foo)

This process recompiles the module's code, re-executes the module-level code, and updates the module's dictionary with new objects.

Python 2 vs. 3 Considerations

In Python 2, reload() was a builtin. However, in Python 3, it was moved to the imp module. In Python 3.4, importlib was introduced as the recommended approach.

Implications for Module Objects

It's important to note that module objects are not discarded when reloaded. Instead, they are updated to reference the new objects. This means that external references to old objects will need to be updated as well.

Example Usage

To effectively reload a module, you can follow this iterative approach:

from importlib import reload
import foo

while True:
    # Do some things.
    if is_changed(foo):
        foo = reload(foo)

By using this approach, you can seamlessly update your services without restarting the server, enhancing your application's flexibility and efficiency.

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