I'm working on a data analysis project in Python and need to calculate both the mean and median of a dataset. I understand the basic concepts, but I'm looking for a Python code example that demonstrates how to do this efficiently.

Let's say I have a list of numbers:

data = [12, 45, 67, 23, 41, 89, 34, 54, 21]

I want to calculate both the mean and median of these numbers. Could you provide a Python code snippet that accomplishes this? Additionally, it would be helpful if you could explain any libraries or functions used in the code.

Thank you for your assistance in calculating these basic statistics for my data analysis project!