CircleCI check only changed files

config.yaml

version: 2.1
executors:
  default:
    working_directory: ~/workspace
    docker:
      - image: circleci/python:3.5
jobs:
  lint:
    executor:
      name: default
    steps:
      - checkout
      - run: sudo pip install flake8
      - run:
          name: Lint files
          command: |
            make check-syntax-errors check-style
            .circleci/flake8-lint.sh
workflows:
  ci:
    jobs:
      - lint

config.yaml-pipeline

version: 2.1
executors:
  default:
    working_directory: ~/workspace
    docker:
      - image: circleci/python:3.5
jobs:
  lint:
    executor:
      name: default
    steps:
      - checkout
      - run: sudo pip install flake8
      - run:
          name: Lint files
          command: |
            CHANGED_FILES=$(git diff --name-only << pipeline.git.base_revision >> <<pipeline.git.revision>> -- "*.py")  # CircleCI pipeline should be enabled
            echo ${CHANGED_FILES}
            echo ${CHANGED_FILES} | xargs --no-run-if-empty flake8
workflows:
  ci:
    jobs:
      - lint

flake8.sh

#! /usr/bin/env bash

last_tagged_commit=`git describe --tags --abbrev=0 --first-parent`  # --first-parent ensures we don't follow tags not published in master through an unlikely intermediary merge commit

echo $last_tagged_commit

if ! changes=$(git diff-index --name-only --diff-filter=ACMR --exit-code $last_tagged_commit -- "*.py")
then
  echo "Running flake8 on these changed files:"
  echo $changes
  flake8 $changes
else echo "Changes not detected."
fi