Functions Python Runtime

Functions are blocks of code that run on demand without the need to manage any infrastructure. Develop on your local machine, test your code from the command line (using doctl), then deploy to a production namespace or App Platform — no servers required.

Functions supports Python 3.9 (python:3.9) and Python 3.11 (python:3.11). Specify the desired runtime and version with the runtime key in your project.yml file, or by using the Runtime dropdown when creating a function through the control panel.

The Functions Python runtime passes two parameters to your handler function, and expects either no return value or a properly formatted response dictionary.

A Python Echo Function

Here is a Python function that responds with all the event and context information available to it:

def main(event, context):
    return {
        "body": {
            "event": event,
            "context": {
                "activationId": context.activation_id,
                "apiHost": context.api_host,
                "apiKey": context.api_key,
                "deadline": context.deadline,
                "functionName": context.function_name,
                "functionVersion": context.function_version,
                "namespace": context.namespace,
                "requestId": context.request_id,
            },
        },
    }

This can be useful for getting started with the Functions platform or for debugging.

The runtime expects a function called main to act as the entry point or the handler. This handler function is the only function where the runtime will pass in data and receive responses.

You can set a different function name as the handler using the main key in project.yml.

The main function above takes two parameters, an event dictionary and a context object. It returns them as the body of the response array. This data structure is automatically converted to JSON and returned.

The Python runtime’s context object is not JSON serializable, so each key is manually referenced when creating the response.

Parameters

The handler function is always passed two parameters, event and context.

Note

Information about function parameters that is not language-specific can be found in the Parameters and Responses reference documentation.

The first parameter, event, is the input event that initiated the function. When this is an HTTP event, it’s called a web event.

The second parameter, context, is data about the function’s execution environment, such as memory allocations and time remaining before a timeout.

Both parameters are optional and you may ignore them if your function doesn’t require the information they provide. The parameter list for your handler function should look like one of the following:

• (event, context): Accesses both parameters.
• (event): Accesses only the event parameter.
• (_, context): Accesses only the context parameter (_ is a common convention for unused parameters, though you may need to mark it as unused to satisfy your linter or IDE).
• () : Accesses neither.

Here is a function that uses both parameters to return a personalized Hello world and the function’s version number:

def main(event, context):
    name = event.get("name", "stranger")
    version = context.function_version
    return {"body": f'Hello {name}! This is version {version}'}

If you add this function to your namespace, you can call it by pasting its URL in your browser and adding a name field in a query string at the end:

Note

You can get the URL for your function from the control panel interface, or by running the following command on the command line:

doctl serverless function get <function-name> --url

https://<your-function-url>?name=Sammy

Or use curl to send the input as form data in the body of the request:

curl -d 'name=Sammy' <your-function-url>

Either way, the function returns the response body:

Hello Sammy! This is function version 0.0.2.

Event Parameter

The event parameter is a dictionary. It is structured like the following example:

{
	"http": {
		"headers": {
			"accept": "*/*",
			"accept-encoding": "gzip",
			"user-agent": "curl/7.85.0",
			"x-forwarded-for": "203.0.113.11",
			"x-forwarded-proto": "https",
			"x-request-id": "5df6f6b0d00b58217439c8376fcae23a"
		},
		"method": "POST",
		"path": ""
	},
	"shark": "hammerhead"
}

This example event has had a shark: hammerhead input passed to it. This has been parsed and added as a top-level key to the object.

More details on the information contained in the event parameter is available under the Event Parameter section of the Parameters and Responses reference documentation.

Context Parameter

The context parameter is a class. It has the following properties, shown here with example data:

{
	"activation_id": "5f56b7e9fbd84b2f96b7e9fbd83b2f2e",
	"api_host": "https://faas-nyc1-2ef2e6cc.doserverless.co",
	"api_key": "",
	"deadline": 1675959023728,
	"function_name": "/fn-52ad03a2-8660-4f7c-55a5-81aa8bbe73b1/example",
	"function_version": "0.0.10",
	"namespace": "fn-52ad03a2-8660-4f7c-55a5-81aa8bbe73b1",
	"request_id": "452164dfeced0a7ad91ee675609024e7"
}

Additionally, it has one method, get_remaining_time_in_millis(), which returns an int of the milliseconds remaining before the function times out.

More details on the information contained in the context parameter is available under the Context Parameter section of the Parameters and Responses reference documentation.

Returns

To send a response, your function must return a properly formatted response dictionary. If your function does not need to send a response, you may return an empty dictionary, nothing at all, or omit the return statement entirely.

Here is a response dictionary that would return a string as the response body:

{ "body": "Hello world" }

If the body is a Python dictionary or list, it is automatically serialized as JSON and returned with a Content-Type: application/json header. This function returns the event parameter as JSON:

def main(event, context):
	return { "body": { "event": event } }

You may also specify the response’s status code and headers. The status code can be an integer or a string:

def main(event, context):
	return {
		"body": "Hello world",
		"statusCode": 200,
		"headers": {
			"Content-Type": "text/plain"
		}
	}

More details on the response can be found in the Returns section of the Parameters and Responses reference documentation.

Example Functions

Return JSON

If the body is a dictionary or list, it is automatically serialized as JSON and returned with a Content-Type: application/json header.

def main():
	return {
		"body": [{"type": "hammerhead"}, {"type": "mako"}]
	}

Return an Image

To return an image or other media type, set the correct Content-Type header and return a base64-encoded body:

def main():
	gif = "R0lGODlhAQABAAD/ACwAAAAAAQABAAACADs="
	return {
		"headers": { "Content-Type": "image/gif" },
		"statusCode": 200,
		"body": gif
  }

Return an HTTP Redirect

A 302 status code and location header redirects an HTTP client to a new URL:

def main():
	return {
		"headers": { "location": "https://example.com" },
		"statusCode": 302
  }

Return HTML and Set a Cookie

Set cookies with the Set-Cookie header, and use the Content-Type: 'text/html' header to return HTML content:

def main():
	return {
		"headers": {
			"Set-Cookie": "UserID=Sammy; Max-Age=3600; Version=",
			"Content-Type": "text/html"
		},
		"statusCode": 200,
		"body": "<html><body><h3>hello</h3></body></html>"
	}

More Example Functions

Some more complex example Python functions are available on GitHub:

Python SendGrid Emails

github.com

Python Twilio SMS

github.com

Python Joke API

github.com

Log to the Console

Any text output to stdout and stderr is logged and can be accessed through the doctl command line tool. Use doctl serverless activations logs --follow to follow logs for all functions in the current namespace, or specify a single function with --function.

See the doctl serverless activations logs reference for more information or add the --help flag to the command for help output.

Use Python Packages and Dependencies

Python functions can import external dependencies. Some common packages are included in the Python runtime (version 3.11 and higher), and others can be deployed using a requirements.txt file and a build script.

Use Packages Provided by the Runtime

Beginning with version 3.11, the Python runtime includes some common PyPI packages. You can import these packages in your functions without providing a requirements.txt and build script.

Each version of the Python runtime will always provide the same major version of its included packages. Minor and patch version updates will be applied throughout the lifetime of a runtime version.

To use these packages, import them in your Python code. Here is an example Python function that uses the pandas package:

import pandas

def main():
	return { "body": str(pandas) }

Python 3.11 Runtime

The following packages are provided by the Python 3.11 runtime:

To use a package not provided by the runtime, follow the instructions in the next section to include it in a virtual environment with your deployed function code.

Add Packages With a Virtual Environment

Python functions with external dependencies not provided by the runtime can be deployed with a build script and a requirements.txt file.

First make sure that the file containing the handler function is named __main__.py. Here is an example Python function that uses the cowsay package:

import cowsay

def main(event):
	name = event.get("name", "stranger")
	greeting = cowsay.get_output_string('cow', f'Hello {name} from Python!')
	return { "body": greeting }

The requirements.txt file for this function:

cowsay==5.0

A build.sh script is required to create a virtualenv and install the packages:

#!/bin/bash

set -e

virtualenv --without-pip virtualenv

# Uncomment if you're using the Python 3.9 runtime
# pip install -r requirements.txt --target virtualenv/lib/python3.9/site-packages

# Uncomment if you're using the Python 3.11 runtime
# pip install -r requirements.txt --target virtualenv/lib/python3.11/site-packages

The virtualenv must be created with the virtualenv command and be named virtualenv. This script uses the --without-pip flag to avoid installing pip into the virtualenv. This reduces the final size of the built function, freeing up space for other dependencies.

The build system’s built-in pip is used to install requirements directly to the appropriate path using the --target option. If you are building locally, your local machine is the build system and must have the runtime’s version of Python installed, as well as pip and virtualenv.

Make sure the above files are in a properly formatted project directory then deploy with doctl serverless deploy <your-project-directory>. You may use the --remote-build flag to run the build remotely.

Include Files in Built Function

To include arbitrary files with your deployed function (for example, config files and templates), place the files in your function directory. By default, all files in the function directory will be included in the deployed function. This can be customized using .ignore and .include files. See the Build Process reference for details.

Here is an example function that reads text content from a file:

Directory structure:

.
├── packages
│   └── <package-name>
│       └── <function-name>
│           ├── __main__.py
│           └── to_be_included.txt
└── project.yml

    
        
            
def main():
  with open('to_be_included.txt', 'r') as file:
    file_contents = file.read()
    return {
      'body': f'File contents: "{file_contents}"'
    }

        
    

    
        
            
Hello, World!

        
    

When invoked, the response is:

File contents: "Hello, World!"