Specifying dependencies

Dependencies for python applications are declared in a standard requirements.txt file. For example:

Flask==MAJOR.MINOR.PATCH
google-cloud-storage

Replace MAJOR, MINOR, and PATCH with the desired Flask version numbers.

You can use any Linux-compatible Python package in the App Engine flexible environment, including packages that require native (C) extensions.

The Python runtime will automatically install all dependencies declared in your requirements.txt during deployment.

Installing dependencies locally

When developing and testing your application locally, we recommended you use venv to isolate your application's dependencies from your system packages. This also ensures that your dependencies will be the same version on your local machine and the deployed application.

To use venv to install dependencies, complete the following steps:

Mac OS / Linux

Note: These instructions describe how to set up a virtual environment in Python 3. For Python 2 apps, use virtualenv to set up a virtual environment.

1. Create an isolated Python environment:

   python3 -m venv env
   source env/bin/activate

2. If you're not in the directory that contains the sample code, navigate to the directory that contains the hello_world sample code. Then install dependencies:

   cd YOUR_SAMPLE_CODE_DIR
   pip install -r requirements.txt

Windows

Note: These instructions describe how to set up a virtual environment in Python 3. For Python 2 apps, use virtualenv to set up a virtual environment.

Use PowerShell to run your Python packages.

1. Locate your installation of PowerShell.
2. Right-click on the shortcut to PowerShell and start it as an administrator.
3. Create an isolated Python environment.

   python -m venv env
   .\env\Scripts\activate

4. Navigate to your project directory and install dependencies. If you're not in the directory that contains the sample code, navigate to the directory that contains the hello_world sample code. Then, install dependencies:

   cd YOUR_SAMPLE_CODE_DIR
   pip install -r requirements.txt

This ensures that when you run your app locally, only the dependencies that are declared in the requirements.txt file are available. The dependencies installed by App Engine during deployment are based on the contents of the requirements.txt file, not the contents of the env/ directory.

Tip: Often you will not know your exact dependencies. After you install dependencies, you can use pip freeze to write the name and version of all installed packages to your requirements.txt.

Installing a web framework

You'll need to use a web framework to enable your app to serve web requests. You can use any Python web framework including the following:

• Flask
• Django
• Pyramid
• Bottle
• web.py
• Tornado

To use a particular web framework, just add it to your requirements.txt:

Flask==MAJOR.MINOR.PATCH

Installing a WSGI server

Some web frameworks have built-in WSGI servers; however, few of them are suitable for serving production traffic. Most web applications use a standalone WSGI server such as Gunicorn, uWSGI or Waitress. For more information on installing, configuring, and using a WSGI server see application startup.

Installing the Cloud Client Libraries

The Cloud Client Libraries for Python is a client library for accessing Google Cloud services that significantly reduces the boilerplate code you have to write. The library provides high-level API abstractions so they're easier to understand. It embraces idioms of Python, works well with the standard Python library, and integrates better with your codebase.

For example, you can install the corresponding Python client library for Datastore or Cloud Storage to integrate those services with your app.

To install the Python client library for Cloud Datastore:

1. Install the client library locally by using pip:

   pip install google-cloud-datastore

2. Set up authentication. You can configure the Cloud Client Libraries for Python to handle authentication automatically. The client library can automatically handle authentication for you locally as well by using the Google Cloud CLI.

   gcloud auth login
   

3. Use the Datastore Client Libraries reference to implement support for the Cloud Datastore service in your app.

For a complete list of all of the Cloud Client Libraries for Python for the supported Google Cloud services, see APIs & Python Libraries.