Upload to pypi from Gitlab Pipelines

I am simply using the TWINE_USERNAME and TWINE_PASSWORD variables, it worked out of the box.

This is the relevant part in my gitlab-ci.yml (replace the image with your desired one and of course change all the other stuff like stage, cache etc. to your needs):

pypi:
    image: docker.km3net.de/base/python:3
    stage: release
    cache: {}
    script:
        - pip install -U twine
        - python setup.py sdist
        - twine upload dist/*
    only:
        - tags

And add the environment variables in GitLab under Settings->CI/CD->Variables (https://your-gitlab-instance.oerg/GIT_NAMESPACE/GIT_PROJECT/settings/ci_cd):

Here is the successful pipeline:

I got this working, using a modified version of your code:

pypi:
  stage: upload
  script:
  - pip install twine
  - rm -rf dist
  - echo "[distutils]" >> ~/.pypirc
  - echo "index-servers =" >> ~/.pypirc
  - echo "    nexus" >> ~/.pypirc
  - echo "" >> ~/.pypirc
  - echo "[nexus]" >> ~/.pypirc
  - echo "${PYPI_REPO}" >> ~/.pypirc
  - echo "${PYPI_USER}" >> ~/.pypirc
  - echo "${PYPI_PASSWORD}" >> ~/.pypirc
  - python3 setup.py check sdist bdist  # This will fail if your creds are bad.
  - python setup.py sdist bdist_wheel
  - twine upload -r nexus dist/*.tar.gz

The difference is I didn't use the "'" and got rid of the colons in the yaml; instead I set the values of the secrets as e.g., username: myuser