Travis-CI: Do not fail build because of linter warnings

Question

I have an old python project that I am trying to progressively clean up using flake8 (to warn about PEP8 issues). I use Travis for continuous integration and want my build to fail if any unit test fails. However, I do not want my build to fail simply because flake8 produced a warning (e.g., about something minor like trailing white space).

How do I configure Travis to output flake8 warnings (so that I can resolve them as I have time) without causing them to fail the build?

My .travis.yml is below:

language: python
python:
  - "3.6"

install:
  - pip install -r requirements.txt
  - pip install flake8

script:
  - python -m unittest discover -v
  - flake8 .

Example flake8 warnings:

./meta-db/file_system.py:103:80: E501 line too long (108 > 79 characters) 
./meta-db/file_system.py:106:68: W291 trailing whitespace

Answer 1

Adding --exit-zero flag to flake8 allows lint warnings/errors to be displayed without failing the Travis build.

script:
  - python -m unittest discover -v
  - flake8 . --exit-zero # Exit with status code "0" even if there are errors.