Implementation of python's caching (#266)

README.md

@@ -9,6 +9,7 @@ This action sets up a Python environment for use in actions by:
 - optionally installing and adding to PATH a version of Python that is already installed in the tools cache.
 - downloading, installing and adding to PATH an available version of Python from GitHub Releases ([actions/python-versions](https://github.com/actions/python-versions/releases)) if a specific version is not available in the tools cache.
 - failing if a specific version of Python is not preinstalled or available for download.
+- optionally caching dependencies for pip and pipenv.
 - registering problem matchers for error output.
 
 # What's new
@@ -18,6 +19,7 @@ This action sets up a Python environment for use in actions by:
 - Automatic setup and download of Python packages if using a self-hosted runner.
 - Support for pre-release versions of Python.
 - Support for installing any version of PyPy on-flight
+- Support for built-in caching of pip and pipenv dependencies
 
 # Usage
 
@@ -205,6 +207,76 @@ pypy-3.7-v7.3.3rc1 # Python 3.7 and preview version of PyPy
 pypy-3.7-nightly # Python 3.7 and nightly PyPy
 ```
 
+# Caching packages dependencies
+
+The action has built-in functionality for caching and restoring dependencies. It uses [actions/cache](https://github.com/actions/toolkit/tree/main/packages/cache) under the hood for caching dependencies but requires less configuration settings. Supported package managers are `pip` and `pipenv`. The `cache` input is optional, and caching is turned off by default.
+
+The action defaults to searching for a dependency file (`requirements.txt` for pip or `Pipfile.lock` for pipenv) in the repository, and uses its hash as a part of the cache key. Use `cache-dependency-path` for cases where multiple dependency files are used, they are located in different subdirectories or different files for the hash want to be used.
+
+ - For pip, the action will cache global cache directory
+ - For pipenv, the action will cache virtualenv directory
+
+**Please Note:** Restored cache will not be used if the requirements.txt file is not updated for a long time and a newer version of the dependency is available that can lead to an increase in total build time.
+
+The requirements file format allows to specify dependency versions using logical operators (for example chardet>=3.0.4) or specify dependencies without any versions. In this case the pip install -r requirements.txt command will always try to install the latest available package version. To be sure that the cache will be used, please stick to a specific dependency version and update it manually if necessary.
+
+**Caching pip dependencies:**  
+
+```yaml
+steps:
+- uses: actions/checkout@v2
+- uses: actions/setup-python@v2
+  with:
+    python-version: '3.9'
+    cache: 'pip'
+- run: pip install -r requirements.txt
+- run: pip test
+```
+
+**Caching pipenv dependencies:**
+```yaml
+steps:
+- uses: actions/checkout@v2
+- name: Install pipenv
+  run: pipx install pipenv
+- uses: actions/setup-python@v2
+  with:
+    python-version: '3.9'
+    cache: 'pipenv'
+- run: pipenv install
+- run: pipenv test
+```
+
+**Using wildcard patterns to cache dependencies**
+```yaml
+steps:
+- uses: actions/checkout@v2
+- uses: actions/setup-python@v2
+  with:
+    python-version: '3.9'
+    cache: 'pip'
+    cache-dependency-path: '**/requirements-dev.txt'
+- run: pip install -r subdirectory/requirements-dev.txt
+- run: pip test
+```
+
+**Using a list of file paths to cache dependencies**
+```yaml
+steps:
+- uses: actions/checkout@v2
+- name: Install pipenv
+  run: pipx install pipenv
+- uses: actions/setup-python@v2
+  with:
+    python-version: '3.9'
+    cache: 'pipenv'
+    cache-dependency-path: |
+      server/app/Pipfile.lock
+      __test__/app/Pipfile.lock
+- run: pipenv install
+- run: pipenv test
+```
+
 # Using `setup-python` with a self hosted runner
 
 Python distributions are only available for the same [environments](https://github.com/actions/virtual-environments#available-environments) that GitHub Actions hosted environments are available for. If you are using an unsupported version of Ubuntu such as `19.04` or another Linux distribution such as Fedora, `setup-python` will not work. If you have a supported self-hosted runner and you would like to use `setup-python`, there are a few extra things you need to make sure are set up so that new versions of Python can be downloaded and configured on your runner.