As per public statements, Google has ~100 million lines of Python code. Also, Google has used Python very heavily from the start, meaning that some of that code was written in Python 1.x or early 2.x days, before the language had packages, before standard modules like 'logging' or 'unittest', even before booleans(!).

It's just a lot of code to migrate. It takes time.

Disclaimer: Work at Google, wrote some of that code.

Sure, but why not support it in an external facing product? No one externally depends on that old google code.

Started as an internal tool, at least according to medium & other blog posts.

It is in the works [0], and like people said since Google uses Python 2.7 that's the verison that was supported by default.

[0] https://stackoverflow.com/questions/46941308/python-3-suppor...

They can release a version that supports 2.7 much sooner

Jupyter switch really easily from Python2.7 to Python 3 to C# because the front end and backend are separated. Not sure why they are having issue here.