The warnings module writes warning messages to the sys.stderr stream:

import warnings

warnings.warn("This is a drill!")

The output warning also contains a line number:

warn.py:3: UserWarning: This is a drill!
  warnings.warn("This is a drill!")

Python has an option to stop with an error as soon as a warning occurs:

python -W error warnme.py

Dr. Kristian Rother

I am a professional Python trainer, developer and author based in Berlin. I believe everybody can learn programming.

Contact me via:
+49 176 3052 4691


Your tips helped me a lot with designing the workshop and then to make it run smoothly!

Joanna Kasprzak, UAM Poznan

See also