Computational Linguistics 4, Exercise 1: hoped, hopes, hoping

Code (run with py -X utf8, using the chapter's strip_suffix):

for w in ["hoped", "hopes", "hoping"]:
    print(w, "->", strip_suffix(w))

Output from the run:

hoped -> hop
hopes -> hop
hoping -> hop

Why it is wrong: the lemma is "hope". The stripper removes "ed", "es" and "ing"
but cannot know that the silent "e" belongs to the stem. The result "hop" is a
real English word with a different meaning, so the error looks like a correct
answer.

What the Stemming article says: a stem can be a fragment, not a dictionary
word (Porter turns argue, argued, argues, arguing and argus into "argu"), and
suffix stripping is "crude with irregular pairs". Here the stem happens to be a
real word, which hides the mistake.