I was fresh at university, around 2001, and our mathematics professor introduced us to Python with NumPy/SciPy as an alternative to the commercial math tools. There aren't many events that changed my career as much as that. Being exposed only to compiled languages before that, it blew my mind. It was friendly, expressive and came with batteries included.

There was a huge sense of community around Python, that I didn't really see elsewhere in the programming world. It started with these scientific libraries. Python wouldn't be what Python is today without NumPy. It was nice to see in the last years the boost of the Python scientific community, with basically anything machine learning using Python as the DSL.