[solomatov]

The main advantage of Python for you is that you know the language and the libraries, and when you start something new, it's critical that you work on the project, not on learning a new technology.

The main advantage of JVM and CLR for large scale development is support for static types. But, Python has a standard for type annotations (https://www.python.org/dev/peps/pep-0484/) which allow you to have all the language services which are available for static languages (refactoring, completion, etc) available for the Python. Not all libraries have these annotations, but you can provide it yourself, or separate code with annotations from code without annotations.

You should also take into account that JVM, and CLR have much better runtime performance than Python, almost on par with C++, so you should think about this if it's important for your app to use resources as efficiently as possible, but typically it's not as important for SaaS projects.

[chuckus]

True, I've been using type notations with all my Python 3.5+ projects (and works very well with PyCharm), though noting that this is only a recent addition, available (officially) for very recent Python releases and is not enforced out of the box. And yes, delivering on the project is critical, especially for startups at the very beginning where you're still trying to find product-market fit so sudden production changes need to be swift.