diff --git a/.github/workflows/lint-shell.yml b/.github/workflows/lint-shell.yml
new file mode 100644
index 00000000..d0a6c283
--- /dev/null
+++ b/.github/workflows/lint-shell.yml
@@ -0,0 +1,24 @@
+name: Lint shell scripts
+
+on:
+  push:
+    paths:
+      - '.github/workflows/lint-shell.yml'
+      - '**.sh'
+  pull_request:
+    paths:
+      - '.github/workflows/lint-shell.yml'
+      - '**.sh'
+
+jobs:
+  lint:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+
+      # Recursively lint all shell scripts in the repository
+      # See: https://github.com/azohra/shell-linter/blob/latest/README.md
+      - name: ShellCheck 
+        uses: azohra/shell-linter@latest
diff --git a/.github/workflows/test-python.yml b/.github/workflows/test-python.yml
index a2658145..22895e0f 100644
--- a/.github/workflows/test-python.yml
+++ b/.github/workflows/test-python.yml
@@ -4,15 +4,16 @@ on:
   pull_request:
     paths:
       - '.github/workflows/test-python.yml'
+      - 'action-setup.sh'
       - 'compilesketches/**'
 
   push:
     paths:
       - '.github/workflows/test-python.yml'
+      - 'action-setup.sh'
       - 'compilesketches/**'
 
-  # The actions/setup-python action will periodically break the workflow by dropping the Python version we have pinned
-  # Better to catch that before it causes confusion for a contributor
+  # Catch issues resulting from new patch releases of Python in the APT repository
   schedule:
     # run every Tuesday at 3 AM UTC
     - cron: "0 3 * * 2"
@@ -32,29 +33,52 @@ jobs:
     env:
       PYTHON_PROJECT_PATH: ${GITHUB_WORKSPACE}/compilesketches
       PYTHON_PROJECT_TESTS_PATH: ${GITHUB_WORKSPACE}/compilesketches/tests
+      COVERAGE_DATA_FILENAME: coverage.xml
 
     steps:
       - name: Checkout
         uses: actions/checkout@v2
 
-      - name: Set up Python
-        uses: actions/setup-python@v1
-        with:
-          python-version: '3.8.6'
+      - name: Run the set up script
+        id: setup
+        run: |
+          "${{ github.workspace }}/action-setup.sh"
 
-      - name: Install dependencies
+      - name: Install test dependencies
         run: |
-          python -m pip install --upgrade pip
-          pip install --requirement "${{ env.PYTHON_PROJECT_TESTS_PATH }}/requirements.txt"
+          source "${{ steps.setup.outputs.python-venv-activate-script-path }}"
+          "${{ steps.setup.outputs.python-command }}" \
+            -m \
+              pip install \
+                --requirement "${{ env.PYTHON_PROJECT_TESTS_PATH }}/requirements.txt"
 
-      - name: Run Python unit tests and report code coverage
+      - name: Run Python unit tests and record code coverage data
         run: |
+          source "${{ steps.setup.outputs.python-venv-activate-script-path }}"
           export PYTHONPATH="${{ env.PYTHON_PROJECT_PATH }}"
-          coverage run --source="${{ env.PYTHON_PROJECT_PATH }}" --module pytest "${{ env.PYTHON_PROJECT_TESTS_PATH }}"
-          # Display code coverage report in workflow run log
-          coverage report
+          "${{ steps.setup.outputs.python-command }}" \
+            -m \
+              coverage run \
+                --rcfile="${{ env.PYTHON_PROJECT_TESTS_PATH }}/.coveragerc" \
+                --source="${{ env.PYTHON_PROJECT_PATH }}" \
+                --module \
+                  pytest "${{ env.PYTHON_PROJECT_TESTS_PATH }}"
+          # Generate coverage data file for consumption by `codecov/codecov-action`.
+          # Otherwise that action generates the file using the system Python environment, which doesn't work.
+          "${{ steps.setup.outputs.python-command }}" \
+            -m \
+              coverage xml \
+                -o "${{ github.workspace }}/${{ env.COVERAGE_DATA_FILENAME }}"
+
+      - name: Display code coverage report
+        run: |
+          source "${{ steps.setup.outputs.python-venv-activate-script-path }}"
+          "${{ steps.setup.outputs.python-command }}" \
+            -m \
+              coverage report
 
       - name: Upload coverage report to Codecov
         uses: codecov/codecov-action@v1
         with:
+          file: ${{ env.COVERAGE_DATA_FILENAME }}
           fail_ci_if_error: true
diff --git a/Dockerfile b/Dockerfile
deleted file mode 100644
index 45164514..00000000
--- a/Dockerfile
+++ /dev/null
@@ -1,10 +0,0 @@
-FROM python:3.8.6
-
-# Copies your code file from your action repository to the filesystem path `/` of the container
-COPY compilesketches /compilesketches
-
-# Install python dependencies
-RUN pip install -r /compilesketches/requirements.txt
-
-# Code file to execute when the docker container starts up
-ENTRYPOINT ["python", "/compilesketches/compilesketches.py"]
diff --git a/action-setup.sh b/action-setup.sh
new file mode 100755
index 00000000..4022b68f
--- /dev/null
+++ b/action-setup.sh
@@ -0,0 +1,45 @@
+#!/bin/sh
+
+# Set up the Python environment for the action's script to run in
+
+readonly PYTHON_PACKAGE_VERSION='3.8'
+
+# https://stackoverflow.com/a/29835459
+readonly SCRIPT_PATH="$(
+  CDPATH='' \
+  cd -- "$(
+    dirname -- "$0"
+  )" && (
+    pwd -P
+  )
+)"
+
+readonly PYTHON_COMMAND="python${PYTHON_PACKAGE_VERSION}"
+readonly PYTHON_VENV_PATH="${SCRIPT_PATH}/compilesketches/.venv"
+readonly PYTHON_VENV_ACTIVATE_SCRIPT_PATH="${PYTHON_VENV_PATH}/bin/activate"
+
+# Install Python
+sudo apt-get install --yes software-properties-common > /dev/null
+sudo add-apt-repository --yes ppa:deadsnakes/ppa > /dev/null
+sudo apt-get update --yes > /dev/null
+sudo apt-get install --yes python${PYTHON_PACKAGE_VERSION} > /dev/null
+echo "Using Python version: $("$PYTHON_COMMAND" --version)"
+
+sudo apt-get install --yes python3-setuptools > /dev/null
+sudo apt-get install --yes python${PYTHON_PACKAGE_VERSION}-venv > /dev/null
+
+# Create Python virtual environment
+"$PYTHON_COMMAND" -m venv "$PYTHON_VENV_PATH"
+
+# Activate Python virtual environment
+# shellcheck source=/dev/null
+. "$PYTHON_VENV_ACTIVATE_SCRIPT_PATH"
+
+# Install Python dependencies
+"$PYTHON_COMMAND" -m pip install --upgrade pip > /dev/null
+"$PYTHON_COMMAND" -m pip install --quiet --requirement "${SCRIPT_PATH}/compilesketches/requirements.txt"
+
+# Set outputs for use in GitHub Actions workflow steps
+# See: https://docs.github.com/en/free-pro-team@latest/actions/reference/workflow-commands-for-github-actions#setting-an-output-parameter
+echo "::set-output name=python-command::$PYTHON_COMMAND"
+echo "::set-output name=python-venv-activate-script-path::$PYTHON_VENV_ACTIVATE_SCRIPT_PATH"
diff --git a/action.yml b/action.yml
index d0966048..7bbb4c7b 100644
--- a/action.yml
+++ b/action.yml
@@ -43,5 +43,30 @@ inputs:
     required: true
 
 runs:
-  using: 'docker'
-  image: 'Dockerfile'
+  using: composite
+  steps:
+    - name: Run the set up script
+      id: setup
+      shell: bash
+      run: |
+        # Group action setup log output
+        echo "::group::Action set up"
+        "${{ github.action_path }}/action-setup.sh"
+        echo "::endgroup::"
+
+    - name: Run script
+      shell: bash
+      env:
+        INPUT_CLI-VERSION: ${{ inputs.cli-version }}
+        INPUT_FQBN: ${{ inputs.fqbn }}
+        INPUT_LIBRARIES: ${{ inputs.libraries }}
+        INPUT_PLATFORMS: ${{ inputs.platforms }}
+        INPUT_SKETCH-PATHS: ${{ inputs.sketch-paths }}
+        INPUT_VERBOSE: ${{ inputs.verbose }}
+        INPUT_GITHUB-TOKEN: ${{ inputs.github-token }}
+        INPUT_ENABLE-DELTAS-REPORT: ${{ inputs.enable-deltas-report }}
+        INPUT_ENABLE-WARNINGS-REPORT: ${{ inputs.enable-warnings-report }}
+        INPUT_SKETCHES-REPORT-PATH: ${{ inputs.sketches-report-path }}
+      run: |
+        source "${{ steps.setup.outputs.python-venv-activate-script-path }}"
+        "${{ steps.setup.outputs.python-command }}" "${{ github.action_path }}/compilesketches/compilesketches.py"
diff --git a/compilesketches/tests/.coveragerc b/compilesketches/tests/.coveragerc
new file mode 100644
index 00000000..9ca48dd2
--- /dev/null
+++ b/compilesketches/tests/.coveragerc
@@ -0,0 +1,3 @@
+[run]
+omit =
+    */.venv/*