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File : foo_module.py

#file: foo_module.py def foo(): print("Am foo v1")

File : attempt1.py

#file: attempt1.py import sys from time import sleep from importlib import reload import foo_module # <-- import the entire module print(sys.modules['foo_module']) #Lets see if the module is loaded while True: foo_module.foo() #simulate a delay or a condition by when foo_module would have changed sleep(2) #should reload foo_module to get the latest reload(foo_module)

Output:

<module 'foo_module' from 'D:\\pyth\\foo_module.py'> Am foo v1 Am foo v1 Am foo v1 # I go in around this time and change the foo_module print statement to simulate update to a loaded module Am foo v2 # Voila ! reload works ! Am foo v2 Am foo v2

This is good and works as I expected. But the following doesnt work !

File : attempt2.py

#file: attempt2.py import sys from time import sleep from importlib import reload from foo_module import foo # <-- import specific item only #Lets see if the module is loaded print(sys.modules['foo_module']) while True: foo() #simulate a delay or a condition by when foo_module would have changed sleep(2) #try to reload foo_module to get the latest reload(foo_module) #FAILS !

Output: 

<module 'foo_module' from 'D:/pyth\\foo_module.py'> # <-- Module is loaded. isnt it ? Am foo v1 Traceback (most recent call last): File "D:/pyth/attempt2.py", line 10, in <module> reload(foo_module) NameError: name 'foo_module' is not defined

But sys.modules does seem to have the entry for the foo_module in it in both cases ! What am i missing ?

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Credits to https://stackoverflow.com/a/46814062/237105.

# Reload via sys.modules as it is not imported directly reload(sys.modules['foo_module']) # Then, reimport function from foo_module import foo

Total code of yours, fixed:

import sys from time import sleep from importlib import reload from foo_module import foo # <-- import specific item only print(sys.modules['foo_module']) while True: foo() # simulate a delay or a condition by when foo_module would have changed sleep(2) # reload foo_module via sys.modules as it is not imported directly reload(sys.modules['foo_module']) # re-import foo to update it. from foo_module import foo
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7 Comments

Because foo_module isn't visible in the current scope, you never imported it. That's why the original code fails. Therefore you need to access it via sys.modules.
If it is not visible directly, how come from foo_module import foo worked in a line above the problematic line ?
I think you misunderstand. It's about what names are usable in the current context. And from foo_module import foo only imports the name foo, not foo_module. Therefore if you would call it via foo_module.foo() it would give you the same error. And if foo_module is not available as a name in the current scope, you cannot pass it to reload(). Nonetheless, you did of course load the module when you imported foo, therefore it is available in sys.modules. But because it is not available as a name, you have to access it via sys.modules.
Yes. import searches for the module, for reload the module needs to be already imported. import is a python command, reload() is a function. Big difference.
Well, it can't. The command never reaches the reload() function. If you look carefully, you don't give reload() a string, you give it a name: reload(foo_module), not reload('foo_module'). Python already errors because it doesn't know what foo_module should be, before reload() gets called.
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