How to config Gitlab CI just checks commit changed files

[Background]
I have a Python project with config CI on Gitlab. It has a lint stage which will check code quality of all source code when push event or merge request event is triggered. It will take time to check all source code with merge request. And it will not focus on code quality of merge request. It should check code quality on commit change files.

pylint:
  stage: lint
  before_script:
    - mkdir -p public/badges public/lint
    - echo undefined > public/badges/$CI_JOB_NAME.score
    - pip install pylint-gitlab
  script:
    - pip install -r requirements.txt
    - pylint --rcfile=.pylintrc --exit-zero --output-format=text $(find -type f -name "*.py" ! -path "**/.venv/**") | tee /tmp/pylint.txt
    - sed -n 's/^Your code has been rated at \([-0-9.]*\)\/.*/\1/p' /tmp/pylint.txt > public/badges/$CI_JOB_NAME.score
    - pylint --exit-zero --output-format=pylint_gitlab.GitlabCodeClimateReporter $(find -type f -name "*.py" ! -path "**/.venv/**") > codeclimate.json
    - pylint --exit-zero --output-format=pylint_gitlab.GitlabPagesHtmlReporter $(find -type f -name "*.py" ! -path "**/.venv/**") > public/lint/index.html
  after_script:
    - anybadge --overwrite --label $CI_JOB_NAME --value=$(cat public/badges/$CI_JOB_NAME.score) --file=public/badges/$CI_JOB_NAME.svg 4=red 6=orange 8=yellow 10=green
    - |
      echo "Your score is: $(cat public/badges/$CI_JOB_NAME.score)"
  artifacts:
    paths:
      - public
    reports:
      codequality: codeclimate.json
    when: always
  only:
    - develop
    - merge_requests
  tags:
    - docker

[Solution]
Here is a solution to resolve my problems.
I will create another config pylint for merge request event. It just check code quality on commit changed files compare with merge request target branch.

pylint_merge_request:
  stage: lint
  before_script:
    - pip install pylint-gitlab
  script:
    - echo CI_COMMIT_SHA=${CI_COMMIT_SHA}
    - echo CI_MERGE_REQUEST_TARGET_BRANCH_NAME=${CI_MERGE_REQUEST_TARGET_BRANCH_NAME}
    - git fetch origin ${CI_MERGE_REQUEST_TARGET_BRANCH_NAME}
    - FILES=$(git diff --name-only ${CI_COMMIT_SHA} origin/${CI_MERGE_REQUEST_TARGET_BRANCH_NAME} | grep '\.py'$)
    - echo "Changed files are $FILES"
    - pip install -r requirements.txt
    - pylint --rcfile=.pylintrc --output-format=text $FILES | tee /tmp/pylint.txt
  only:
    - merge_requests
  tags:
    - docker

I hope it is helpful for everyone. You can use it for other programing languages on Gitlab.