How do I unload (reload) a Python module?
module, python, python-import, reload
Solution
You can reload a module when it has already been imported by using `importlib.reload()`:
from importlib import reload # Python 3.4+
import foo
while True:
# Do some things.
if is_changed(foo):
foo = reload(foo)
In Python 2, `reload` was a builtin. In Python 3, it was moved to the `imp` module. In 3.4, `imp` was deprecated in favor of `importlib`. When targeting 3 or later, either reference the appropriate module when calling `reload` or import it.
I think that this is what you want. Web servers like Django's development server use this so that you can see the effects of your code changes without restarting the server process itself.
To quote from the docs:
- Python module’s code is recompiled and the module-level code re-executed, defining a new set of objects which are bound to names in the module’s dictionary by reusing the loader which originally loaded the module. The `init` function of extension modules is not called a second time.
- As with all other objects in Python the old objects are only reclaimed after their reference counts drop to zero.
- The names in the module namespace are updated to point to any new or changed objects.
- Other references to the old objects (such as names external to the module) are not rebound to refer to the new objects and must be updated in each namespace where they occur if that is desired.
As you noted in your question, you'll have to reconstruct `Foo` objects if the `Foo` class resides in the `foo` module.
Problem
I have a long-running Python server and would like to be able to upgrade a service without restarting the server. What's the best way do do this? ``` if foo.py has changed: unimport foo <-- How do I do this? import foo myfoo = foo.Foo() ```