How to reload a Python module that was imported in another file?

Question

I am trying to learn how Python reloads modules, but have hit a roadblock. Let's say I have:

dir1\file1.py:

from dir2.file2 import ClassOne
myObject = ClassOne()

dir1\dir2\file2.py:

class ClassOne():
   def reload_module():
       reload(file2)

The reload call fails to find module "file2".

My question is, how do I do this properly, without having to keep everything in one file?

A related question: When the reload does work, will myObject use the new code?

thank you

There is little use for reloading. What are you trying to do? — S.Lott
– S.Lott, Commented Jul 3, 2009 at 19:17
S.Lott is right, you should explain a little bit more what your actual case is, because the example code looks like something you usually wouldn't want to do. — balpha
– balpha ♦, Commented Jul 3, 2009 at 19:19
Basically what I want to do is have objects running code in edit windows, which the user can change while the system is running. The objects would have a regular "step()" function being called, where the user should change the code. This will alter the behavior of the objects as the program runs. — user129975
– user129975, Commented Jul 3, 2009 at 19:30

Alex Martelli · Accepted Answer · 2009-07-03 19:17:59Z

3

   def reload_module():
       import file2
       reload(file2)

However, this will not per se change the type of objects you've instantiated from classes held in the previous version of file2. The Python Cookbook 2nd edition has a recipe on how to accomplish such feats, and it's far too long and complex in both code and discussion to reproduce here (I believe you can read it on google book search, or failing that the original "raw" version [before all the enhancements we did to it], at least, should still be on the activestate cookbook online site).

answered Jul 3, 2009 at 19:17

Alex Martelli

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8 Comments

Alex Martelli Over a year ago

reload needs as its argument a module object; import binds that module object into the current naming scope. Essentially a module file2 containing this code is able to "refresh itself in memory" on request (if the source was changed), net of the issue with objects instantiated with classes from previous versions, which I've mentioned in my answer.

balpha Over a year ago

Sorry, I had just deleted my question (after it became clear to me). I essentially asked what the point of this importing twice in a row (which it really isn't) would be.

user129975 Over a year ago

Thanks Alex. I tried this and it works, insofar as it doesn't throw any errors. I still need to reload those objects somehow. I noticed you wrote that book. Cool...!

Alex Martelli Over a year ago

Co-edited it (with my wife in the 2nd ed), yes; the original recipe I mention was from Michael Hudson, if I recall correctly, but Anna and I helped enhance most recipes quite substantially (and not all authors put the enhancements back into the online site).

Alex Martelli Over a year ago

(BTW, if this answer helps, what about accepting it? if you need to update code within objects you should probably open another question anyway, as it's quite a different issue).

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