Python is a scripting language with a large amount of support among open source developers. First created in 1991, Python remained a niche language that was popular for mathmatical tasks. The breakout of Ruby as a new, popular language in the early 2000's, Python got a second chance as part of the open source stack for online web applications. It's clean syntax has made it popular among beginning programmers, making Python experience a lot more common with accomplished software developers. Like Node and PHP, it has a vast library of functionality available from open source projects made available with PIP, the Python Package Index.
Django is one of Python's most popular projects and can be found in most web apps found online. It is at the heart of CMS apps like Mezzanine, Django CMS and the Cartridge e-commerce project. Django is a mature framework that contains a built in ORM, migration system and package format that makes building a website or service fast and efficient. Once you have a solid foundation built with Django, adding your specific features on top can be done in a clean and well structured way.
If you aren't looking for a large framework and want an agile micro-framework, Flask has the minimalist design you want. Perfect for web apps and RESTful APIs, Flask is perfect for small projects and unit testing.
Python's history with math and science means you also get access to some of the most cutting edge features like machine learning with TensorFlow, image recognition and processing with OpenCV and powerful Blockchain libraries. Many of these libraries hook in directly to functionality made with compiled code that allows your application to scale under high loads.
Python is one of the most mature development stacks available at the moment. Projects available for use have a long history of support, bug fixes and work across operating systems like Windows, OSX and Linux. Cloud services like Azure and AWS can be spun up and start serving Python based services in minutes.
One of the reasons Python is Parthenon's favorite development stack is the few risks you take by using it for web based services. There is no real risk to choosing Python unless it is not the best fit for your project.