Your First Function: Python

This guide takes you through the process of writing a Cloud Function using the Python runtime. There are two types of Cloud Functions:

  • An HTTP function, which you invoke from standard HTTP requests.
  • A background function, which you use to handle events from your Cloud infrastructure, such as messages on a Cloud Pub/Sub topic, or changes in a Cloud Storage bucket.

The sample shows how to create a simple HTTP function.

Guide structure

  1. Creating a GCP project using Cloud SDK
  2. Creating a function
  3. Specifying dependencies
  4. Deploying your function
  5. Testing your function

Creating a GCP project using Cloud SDK

  1. Sign in to your Google Account.

    If you don't already have one, sign up for a new account.

  2. In the Cloud Console, on the project selector page, select or create a Cloud project.

    Go to the project selector page

  3. Make sure that billing is enabled for your Google Cloud project. Learn how to confirm billing is enabled for your project.

  4. Enable the Cloud Functions and Cloud Build APIs.

    Enable the APIs

  5. Install and initialize the Cloud SDK.
  6. Update and install gcloud components:
    gcloud components update
  7. Need a command prompt? You can use the Google Cloud Shell. The Google Cloud Shell is a command line environment that already includes the Google Cloud SDK, so you don't need to install it. The Google Cloud SDK also comes preinstalled on Google Compute Engine Virtual Machines.

  8. Prepare your development environment.

    Go to the Python setup guide

Creating a function

  1. Create a directory on your local system for the function code:

    Linux or Mac OS X

    mkdir ~/helloworld
    cd ~/helloworld
    

    Windows

    mkdir %HOMEPATH%\helloworld
    cd %HOMEPATH%\helloworld
    
  2. Create a main.py file in the helloworld directory with the following contents:

    from flask import escape
    
    def hello_http(request):
        """HTTP Cloud Function.
        Args:
            request (flask.Request): The request object.
            <https://flask.palletsprojects.com/en/1.1.x/api/#incoming-request-data>
        Returns:
            The response text, or any set of values that can be turned into a
            Response object using `make_response`
            <https://flask.palletsprojects.com/en/1.1.x/api/#flask.make_response>.
        """
        request_json = request.get_json(silent=True)
        request_args = request.args
    
        if request_json and 'name' in request_json:
            name = request_json['name']
        elif request_args and 'name' in request_args:
            name = request_args['name']
        else:
            name = 'World'
        return 'Hello {}!'.format(escape(name))

    This example function takes a name supplied in the HTTP request and returns a greeting, or "Hello World!" when no name is supplied.

Specifying dependencies

Dependencies in Python are managed with pip and expressed in a metadata file called requirements.txt. This file must be in the same directory as the main.py file that contains your function code.

  1. Create a requirements.txt file in the helloworld directory.

  2. Add the function's dependency, in this case the Flask package, to your requirements.txt file by adding the following line:

    Flask==1.0.2
    

Deploying the function

To deploy the function with an HTTP trigger, run the following command in the helloworld directory:

gcloud functions deploy hello_http --runtime python38 --trigger-http --allow-unauthenticated

The --allow-unauthenticated flag lets you reach the function without authentication. To require authentication, omit the flag.

Testing the function

  1. When the function finishes deploying, take note of the httpsTrigger.url property or find it using the following command:

    gcloud functions describe hello_http
    

    It should look like this:

    https://GCP_REGION-PROJECT_ID.cloudfunctions.net/hello_http
  2. Visit this URL in your browser. You should see a "Hello World!" message.

    Try passing a name in the HTTP request, for example by using the following URL:

    https://GCP_REGION-PROJECT_ID.cloudfunctions.net/hello_http?name=NAME

    You should see the message "Hello NAME!"

Viewing logs

Using the command-line tool

Logs for Cloud Functions are viewable in the Stackdriver Logging UI, and via the gcloud command-line tool.

To view logs for your function with the gcloud tool, use the logs read command, followed by the name of the function:

gcloud functions logs read hello_http

The output should resemble the following:

LEVEL  NAME        EXECUTION_ID  TIME_UTC                 LOG
D      hello_http  pdb5ys2t022n  2019-09-18 23:29:09.791  Function execution started
D      hello_http  pdb5ys2t022n  2019-09-18 23:29:09.798  Function execution took 7 ms, finished with status code: 200

Using the Logging dashboard

You can also view logs for Cloud Functions from the Cloud Console.