How to Reload a Python Module Without Restarting the Server?

Reloading Python Modules for Server Upgrades

Maintaining long-running Python servers can require upgrades without restarting the entire server. One approach for this is to unload and reload specific modules.

Question: How to Unload and Reload a Python Module?

To unload a previously imported module and load its updated version without restarting the server:

Answer: Use the importlib.reload() Function

For Python 3.4 , use the importlib.reload() function:

from importlib import reload
import foo

while True:
    # Perform actions
    if is_changed(foo):
        foo = reload(foo)

For Python 2, use the imp module's reload function.

Rebinding References

After reloading a module, its objects will be recreated, but external references will need to be updated. In the example provided, if Foo objects reside in the foo module, you'll need to recreate them.

This technique is commonly used for hot reloading in Django's development server, allowing changes in code to be reflected without restarting the server.

Python Module Reloading Details

Importlib.reload() recompiles the module's code, re-executes the module-level code, and updates the module's dictionary with new objects. Old objects will be garbage collected when reference counts drop to zero.

Unbound references to old objects outside the module will need to be manually updated if desired.

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