It is unclear what your problem is.
- Did you “define”
stkand you are surprised Python does not find it?
- You do not know how to “define”
stk refers to the stk package from pypi. You installed it? Did you import it?
It is also desirable to show code as text. By using a screenshot, you exclude people from helping you. People are using this site through e-mail, they don’t see your screenshot, as do people who use screen readers. Please post code as text.
To see how to, read this: