[nostrademons]

It depends how you define "mainstream".

Python was definitely around, had a very strong community, and a number of very significant programs written in it. (Among them: the first versions of BitTorrent and Google.) However, if you were a random dev applying for a random job, you would most likely have to work in C++, Java, or C#. It was relatively difficult getting a job where you would write the majority of your code in Python. Certainly they existed, and many jobs would have you write small one-off scripts in Python, but the actual core product would usually be one of Java/C#/C++.

Remember that in 2009, Google had 20K employees while IBM (which was a major booster of Java) had 400K. And at Google, Python wasn't really allowed for major projects (Search had been rewritten from Python to C++ when it got big in 2000), so you'd be using Java or C++ anyway. Data science wasn't really a thing, and if you did machine learning you used frameworks like Weka or home-grown stuff.