Turn text into a string of letters in python?

So I am trying to make a piece if code that can take a string, ignore all plain text in it, and return a list of numbers but I am running into trouble.

basically, I want to turn "I want to eat 2 slices of pizza for dinner, and then 1 scoop of ice cream for desert" into [2,1] (just an example)

    dummy = dummy.split(" ")
                    j = 0
                    for i in dummy:
                        dummy[j]=i.rstrip("\D")
                        j+=1
                        print(dummy[j-1])

is what i have tried but it didn't remove anything. i tried the rstrip("\D") because i thought that was supposed to remove text but does not seem to work for a list.

any ideas where i went wrong or ways to fix this?

Turn text into a string of letters in python?