Is there a way to start unit tests which cover only changed code?

In my Python project, we have a big number of unit tests (some thousands). Though they are logically distributed between files and classes, I need sometimes a lot of time in order to find ones, which cover the functionality I'm changing.

Of course, I can run all test from some specific file/class, but again because of big number of that tests, It'll be time-consuming to run them continuously (I'm executing unit tests each time after saving a file in my IDE).

So in general I need some solution which will do following activities at a time:

• Tracks which files have been changed since last file saving
• Traces dependencies between code that have been changed in those files and unit tests which cover that code
• Selectively executes only those unit tests which cover the code that has been affected

Does anyone have idea about something similar?

Thanks!