How do you reload a Django model module using the interactive interpreter via "manage.py shell"?

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I know how to reload a regular Python module within a regular Python interpreter session. This question documents how to do that pretty well:

How do I unload (reload) a Python module?

For some reason, I am having trouble doing that within Django's "manage.py shell" interpreter session. To recreate my issue, start the basic Django tutorial found here:

Writing your first Django app, part 1

After creating the "polls" application and "Poll" class, start up the interpreter via "manage.py shell" and import the "polls" app into it.

import polls.models as pm

Create a new "Poll" object:

p = pm.Poll()

All is well and good so far. Now go back to your source and add any arbitrary method or attribute. For example, I've added:

def x(self):
    return 2+2

Now go back to the interpreter and "reload" the module:

reload(pm)

Now try to use your new method or attribute:

p1 = pm.Poll()
p1.x()

You'll get this message:

'Poll' object has no attribute 'x'

What gives? I've also tried rerunning the import command, importing the module using different syntax, deleting all references to any "Poll" objects or to the "Poll" class. I've also tried this with both the IPython interpreter and with the plain Python (v2.6) interpreter. Nothing seems to work.

Using the same techniques with an arbitrary Python module in a regular interpreter session works perfectly. I just can't seem to get it to work in Django's "shell" session.

By the way, if it makes any difference, I'm doing this on a Ubuntu 9.04 machine.

django python
9 Answers

Well, I think I have to answer to this. The problem is that Django caches its models in a singleton (singleton like structure) called AppCache. Basically, to reload Django models you need to first reload and re-import all the model modules stored in the AppCache. Then you need to wipe out the AppCache. Here's the code for it:

import os
from django.db.models.loading import AppCache
cache = AppCache()

curdir = os.getcwd()

for app in cache.get_apps():
    f = app.__file__
    if f.startswith(curdir) and f.endswith('.pyc'):
        os.remove(f)
    __import__(app.__name__)
    reload(app)

from django.utils.datastructures import SortedDict
cache.app_store = SortedDict()
cache.app_models = SortedDict()
cache.app_errors = {}
cache.handled = {}
cache.loaded = False

I've put all of this in a separate file called reloadmodels.py in the root directory of my Django site. Using IPython I can reload everything by running:

%run ~/mysite/reloadmodels.py
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From the answers of Seti Volkylany and pv

  1. Install IPython: pip install ipython
  2. Run python manage.py shell : the symbol at the beginning of a line should now be In [1]: (in cmd it was >>>)
  3. Run ipython profile create

  4. Go in ~/.ipython/profile_default/ipython_config.py and open it in a text editor and add these two lines at the end:

    c.InteractiveShellApp.extensions = ['autoreload']
    c.InteractiveShellApp.exec_lines = ['%autoreload 2']

You can now run python manage.py shell, edit your models without having to write %autoreload 2

user_31542740

Enable IPython autoreload extension before importing any code:

%load_ext autoreload
%autoreload 2

I use it with the regular django shell and it works perfectly, although it does have some limitations:

*Caveats:

Reloading Python modules in a reliable way is in general difficult, and unexpected things may occur. %autoreload tries to work around common pitfalls by replacing function code objects and parts of classes previously in the module with new versions. This makes the following things to work:

  • Functions and classes imported via ‘from xxx import foo’ are upgraded to new versions when ‘xxx’ is reloaded.
  • Methods and properties of classes are upgraded on reload, so that calling ‘c.foo()’ on an object ‘c’ created before the reload causes the new code for ‘foo’ to be executed.

Some of the known remaining caveats are:

  • Replacing code objects does not always succeed: changing a @property in a class to an ordinary method or a method to a member variable can cause problems (but in old objects only).
  • Functions that are removed (eg. via monkey-patching) from a module before it is reloaded are not upgraded.
  • C extension modules cannot be reloaded, and so cannot be autoreloaded.*

source: https://ipython.org/ipython-doc/3/config/extensions/autoreload.html#caveats

Another great option is to write your code in a separate script and send it to django shell, like this:

manage.py shell < my_script.py
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