How to filter DeprecationWarnings that happen during importing?

Question

We are updating our application from Django 1.6 to 1.7.

We see a lot of these message:RemovedInDjango18Warning

Is there a way to filter them? They get emitted during importing.

We tried warnings.filterwarnings('ignore', '...') but the warnings get emitted before we call warnings.filterwarnings().

How can I filter these warnings which happen during importing?

Answer 1

Quickfix

To silence it only when you run manage.py, add these lines after import sys:

# ...
import sys

if not sys.warnoptions:
    sys.warnoptions += [None]

# ...

If you also want to silence it from your WSGI server (i.e. Apache), update your_project/wsgi.py and add the following lines after import os:

# ...
import os
import sys

if not sys.warnoptions:
    sys.warnoptions += [None]

# ...

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Explanation

The reason this works is because of how django.utils.log.configure_logging() handles it:

def configure_logging(logging_config, logging_settings):
    if not sys.warnoptions:
        # Route warnings through python logging
        logging.captureWarnings(True)
        # RemovedInNextVersionWarning is a subclass of DeprecationWarning which
        # is hidden by default, hence we force the "default" behavior
        warnings.simplefilter("default", RemovedInNextVersionWarning)
    # ...

It's deliberately called early in the boot process as part of django.setup(), which explains why errors were emitted before you were able to silence them further down the stack.

Adding a new element to sys.warnoptions forces it to evaluate to True, bypassing the logic. This is harmless since it's only used during python startup when loaded by the warnings module.

RemovedInNextVersionWarning is just an alias for RemovedInDjango18Warning in Django 1.7. It is set to RemovedInDjango19Warning in 1.8, and so on for future versions -- this code should be future proof for this type of DeprecationWarning.

---

Command line methods

Note that sys.warnoptions is normally set during python startup based on the -W argument when calling python. Therefore, a simple way to just silence the warnings when you use the dev server is python -W123 manage.py runserver. This requires no modification of files, but does result in a single harmless warning at startup since 123 is just a placeholder and not a valid warning action.

Another way is python -Wi::DeprecationWarning manage.py runserver, though this will ignore ALL DeprecationWarnings, including possibly ones of interest which are not RemovedInDjango18Warning.