How do I get warnings.warn to issue a warning and not ignore the line?

Question

I\'m trying to raise a DeprecationWarning, with a code snippet based on the example shown in the docs. http://docs.python.org/2/library/warnings.html#warnings.w

Answer 1

The warnings module implements filtering of warnings based on certain conditions. You can show the default filters by printing warnings.filters:

$ python -c "import warnings; print(warnings.filters)"
[('ignore', None, , None, 0),
 ('ignore', None, , None, 0),
 ('ignore', None, , None, 0),
 ('ignore', None, , None, 0)]

As you can see, DeprecationWarning is ignored by default. You can use the functions in the warnings module and the -W command-line option to Python to configure the filters -- see the documentation for details.

Example:

$ python -Wall
Python 2.7.3 (default, Sep 26 2013, 20:03:06) 
[GCC 4.6.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import warnings
>>> warnings.warn("test", DeprecationWarning)
__main__:1: DeprecationWarning: test