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Use Azure Functions to Find Primes

Create an Azure Function in Python that takes an integer and returns a Boolean value of whether or not the number is prime.

Use the Azure Functions Command Line Interface (CLI) to create a new Python Azure Function App

If you are at an event, run the following command on the CLI:

docker run --rm -v ${PWD}:/pwd/ -w /pwd/ -p 7071:7071 -it aaronmsft/azure-functions-core-tools:latest bash
# create a virtual environment
python3.6 -m venv env
. env/bin/activate

Create a directory for the sample code and cd into it:

mkdir python_azure_func
cd python_azure_func

Create a virtual environment. This is a requirement to create a Python Azure Functions project:

py -3.6 -m venv .env
.\.env\Scripts\activate

Initialize a new Azure Functions App project.

func init prime_calculator

Highlight python (preview) with the arrow keys in the list of worker runtimes, press Enter to select. You should see output resembling:

Installing wheel package
Installing azure-functions==1.0.0b3 package
Installing azure-functions-worker==1.0.0b4 package
Running pip freeze
Writing .funcignore
Writing .gitignore
Writing host.json
Writing local.settings.json
Writing path\to\prime_calculator\.vscode\extensions.json

A new folder named prime_calculator is created. Change directory into this folder:

cd prime_calculator

Create an HTTP Triggered Azure Function

Execute the following command to create a new Azure Function in your app:

func new

Highlight HTTP trigger with the arrow keys in the list of templates, press Enter to select.

Note: if you get the error Unable to find project root. Expecting to find one of host.json, local.settings.json in project root. you likely need to change directory into the project directory, cd prime_calculator.

You will be prompted to name your function:

Function name: [HttpTrigger]

Name your function is_prime. Hit Enter and the CLI will create the files for this Function. The Function App file structure should now look like this:

prime_calculator
│   .funcignore         # Functions listed here will be excluded from deployment
│   .gitignore          # files and directories not to be checked into source control
│   host.json           # runtime settings, including which version of Azure Functions to use
│   local.settings.json # included in the .gitignore by default, these settings will be used when running locally
│   requirements.txt    # modules required to be installed for running the Function App
│
├───.vscode
│       extensions.json # read by VSCode to set extensions
│
└───is_prime            # directory holding all files for our `is_prime` Function
        function.json   # defines that __init__.py will be called and which bindings are used
        sample.dat      # contains a sample input for the Function
        __init__.py     # this module will be called when the Function is run

The default Function created for HTTPTrigger will take a name argument and greet the user.

Testing the Default Function in the Browser

To run the app locally, execute:

func host start

Once running, you should see:

Http Functions:

        is_prime: [GET,POST] http://localhost:7071/api/is_prime

This lists the endpoints made available by the app. In this case, only one URL http://localhost:7071/api/is_prime which will run the is_prime Function and accepts two HTTP methods, GET and POST.

To test the app, open any browser and go to the given URL. You should see a plain HTML page with the text Please pass a name on the query string or in the request body. Change the URL so that it reads http://localhost:7071/api/is_prime?name=PyCon. The page at this URL should display the text Hello PyCon!.

Note: If you are not seeing the correct response here, it would be a good time to ask for assistance. Understanding how to pass values to the Function using a query string is important for the rest of the lab.

Before moving on, shut down the app. In the command prompt, type ctrl+c, you will be asked to confirm Terminate batch job (Y/N)?. Respond with Y.

Writing is_prime

Execute code . to open the Azure Functions App in Visual Studio Code. In the app, open the file prime_calculator/is_prime/__init__.py.

This is the code you ran in the section above. If the HTTP endpoint receives a query string with a value mapping to the key name it returns Hello {name}!. Otherwise, it returns a 400 code with an error message.

Edit this code to add a function that calculates if an integer is a prime number. In the __init__.py file, add to the top of the file:

import math

and to the bottom of the file:

def is_prime(number: int) -> bool:
    """Tests primeness of number, returns true if prime."""
    min_divisor = 2
    max_divisor = math.ceil(math.sqrt(number))
    for divisor in range(min_divisor, max_divisor + 1):
        if number % divisor == 0:
            return False
    return True

Edit the main function in __init__.py to take an int as input and check if it's a prime number or not with the function.

def main(req: func.HttpRequest) -> func.HttpResponse:
    logging.info('Python HTTP trigger function processed a request.')

    number = req.params.get('number')
    try:
        number = int(number)
    except TypeError:
        return func.HttpResponse(
             "Please pass an integer corresponding to the key `number` on the query string or in the request body",
             status_code=400
        )

    response = "is prime" if is_prime(number) else "is composite"
    return func.HttpResponse(f"{number} {response}.")

Save the file and return to the terminal. To run the updated Azure Function App, execute:

func host start

Once running, you should see:

Http Functions:

        is_prime: [GET,POST] http://localhost:7071/api/is_prime

Visit the URL in a browser. You should get the response "Please pass an integer corresponding to the key `number` on the query string or in the request body". Try passing the Azure Function an integer by visiting the URL:

http://localhost:7071/api/is_prime?number=9

You should get the response "9 is composite".

Next Steps