What is the meaning of angle brackets in Python?

That is Cython's syntax for type casting/coercion. It is not plain Python. Notice the file extension is .pyx

You can learn more about them in the documentation for Cython.

Here's an example taken from the doc page:

cdef char *p, float *q
p = <char*>q

Using Cython is not uncommon with projects like scikit-learn, where one gains significant optimisations by mixing readable Python with blazing-speed C.

Take a look at Cython documentation, about types.

Additionally you could note that the file extension is .pyx and on the top of the file there are cimport statements.