How Can I Efficiently Reload Python Modules for Serverless Upgrades Without Restarting the Server?

Reloading Modules in Python for Serverless Upgrades

When running extended Python servers, reloading modules allows for service upgrades without server restarts. One of the common issues in accomplishing this is efficiently unloading the old module before reloading.

Solution: Using importlib.reload()

Python provides a built-in function, importlib.reload(), specifically designed for module reloading. This is an effective solution, especially for Python 3.4 and above.

from importlib import reload  # Python 3.4+
import foo

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

Previously, in Python 2, reload was a builtin. For Python 3, it was moved to the imp module. However, in 3.4, imp was deprecated in favor of importlib. Hence, when targeting Python 3 or later, either reference the appropriate module when calling reload or import it.

Implementation Example

Various web servers, like Django's development server, utilize this method to enable dynamic updates without server process restarts. It is imperative to note that only the module-level code is re-executed, while the init function of extension modules remains untouched. Also, be aware that old objects will only be reclaimed when their reference counts drop to zero.

In your specific scenario, if the Foo class is defined in the foo module, you will need to recreate Foo objects after reloading the module.

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