Set environment variable from python script

I’ve been trying to set an env variable from python script and pass it at build-arg but it doesn’t work.
echo prints the info however the variable is not set in a container after build completed.
Here is the job I am using:

build-and-push-image-fe:
machine:
  image: ubuntu-1604:201903-01
steps:
  - checkout
  - run:
      command: |
        pyenv global 3.7.0 && \
        export VUE_APP_BACKEND_VERSION=$(python3 get_release_version.py) && \
        echo $VUE_APP_BACKEND_VERSION >> $BASH_ENV && \
        echo $VUE_APP_BACKEND_VERSION
  - aws-ecr/build-and-push-image:
      repo: "${REPO_NAME}"
      tag: "fe-${CIRCLE_SHA1}"
      path: "./"
      dockerfile: "fe.Dockerfile"
      extra-build-args: "--build-arg BASE_URL=$BASE_URL --build-arg VUE_APP_URL=$VUE_APP_URL --build-arg VUE_APP_AUTH_BASE_URL=$VUE_APP_AUTH_BASE_URL --build-arg VUE_APP_BACKEND_VERSION=$VUE_APP_BACKEND_VERSION"

And in the Dockerfile I have this:

ARG BASE_URL
ARG VUE_APP_URL
ARG VUE_APP_AUTH_BASE_URL
ARG VUE_APP_BACKEND_VERSION