When I wrote the ASP.NET Core Website that calculates the factorial of a number I promised myself I would write a Python client that uses the factorial service. After a minor change to the website to handle custom http headers, I wrote a quick Python client using the Requests http library for Python. Here are the details.

Custom Headers and ASP.NET Core

The ASP.NET Core Website that calculates a factorial returns results like this when running in a browser.

ASP.NET Core Routing Tutorial Calculating a Factorial

This is fine for viewing in a browser, but for api-like clients it is better to just return the number without the formatting. Therefore, I made a minor change to factorialRequestHandler to look for a custom http header from my Python client and emit only the factorial for those requests. Here is the new code for Startup.

    public class Startup {
        public void ConfigureServices(IServiceCollection services) {

        public void Configure(IApplicationBuilder app) {

            var rb = new RouteBuilder(app);

            RequestDelegate factorialRequestHandler = c => {
                var number = c.GetRouteValue("number") as string;

                int value;
                if (Int32.TryParse(number, out value)) {
                    value = Math.Abs(value);
                    var results = Factorial.Calculate(value);

                    var response = $"{number}! = {results}";

                    if (c.Request.Headers.ContainsKey("user-agent")
                    && c.Request.Headers["user-agent"].Equals("python-app"))
                        response = results.ToString();

                    return c.Response.WriteAsync(response);

                return c.Response.WriteAsync("${number} is not an integer.");

            rb.MapGet("factorial/{number:int}", factorialRequestHandler);

            var routes = rb.Build();


If the user-agent in the http headers is set to "python-app", the service just returns the factorial and not the formatted string.

To be clear, in a browser without the custom http header, the factorial service will return:

15! = 1307674368000

When using the Python web client with the custom http header it will return:


Python Web Client using Requests Library

Now comes the easy part- creating a Python web client to list the factorials for numbers 1 through 10.

I really like the Requests http library for Python so I install it using pip:

pip install requests

Now I write a simple Python script that calls the factorial service of the ASP.NET Core Website to calculate the factorial for numbers 1 - 10. Here is the code.

import requests

headers = {'user-agent': 'python-app'}

for i in range(1, 11):
    r = requests.get('http://localhost:5000/factorial/' + str(i), headers=headers)
    print '{:2}! = {}'.format(i, r.text)

Here is the output.

 1! = 1
 2! = 2
 3! = 6
 4! = 24
 5! = 120
 6! = 720
 7! = 5040
 8! = 40320
 9! = 362880
10! = 3628800



I absolutely love learning both Python and ASP.NET Core at the same time, and I hope using the combination in this article is interesting to both Python and ASP.NET Core enthusiasts. In addition to a bunch of other tutorials, I know I want to write the service using Flask as well as using ASP.NET Core Web API. Thank you for reading!

P.S. My online cryptography class starts today!

Posted by Koder Dojo

I am learning both Python and ASP.NET Core, and I was able to use both when creating a Python web client to use the factorial service I created as an ASP.NET Core Website. If you are learning one or both of these technologies, I hope you find my articles useful. My Python cryptography class starts today so I think it might be time to write code dealing with classic ciphers :)

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