Help with regular expression

Question

Python

I'm sorting out the base of the cladder, in particular, I need to get the case number from the records:
39/43k1str3
34kB
(it can be not only a number, but also a symbol) I
started doing it:
к([\d\.\W]+)стр{0,1}but it only finds records with the structure, in general, can anyone solve such a problem?

Answer 1

k(.+?)(str)?

Answer 2

k([\d\w]).*$

Answer 3

k([0-9A-Z]+) - right?
In general, there are few examples, it is difficult to understand what exactly is needed