pip cache

.github/workflows/ci.yaml

@@ -39,7 +39,17 @@ jobs:
       if: startsWith(matrix.os, 'macos')
       run: |
         brew install ta-lib
-    # TODO: set up pip cache
+    - name: Get pip cache dir
+      id: pip-cache
+      run: |
+        echo "::set-output name=dir::$(pip cache dir)"
+    - name: pip cache
+      uses: actions/cache@v2
+      with:
+        path: ${{ steps.pip-cache.outputs.dir }}
+        key: ${{ runner.os }}-pip-${{ hashFiles('etc/requirements_locked.txt') }}
+        restore-keys: |
+          ${{ runner.os }}-pip-
     - name: Install requirements
       run: |
         python -m pip install -r etc/requirements_build.in -c etc/requirements_locked.txt