Computational Linguistics 6, Exercise 2: John hit the ball

Code (run with py -X utf8, after the chapter's script):

rules["NP"].append(("Name",))
lexicon["Name"] = {"john"}
for t in parse("john hit the ball".split()):
    print(show(t))
print(len(parse("john hit the ball".split())))

Output from the run:

[S [NP john] [VP hit [NP the ball]]]
1

One parse.

Comparison with the Parse tree article's description (S root; NP John; VP
containing V hit and an NP made of D the and N ball):
- Same shape: S -> NP VP, with the VP holding the verb and an NP.
- Label differences: the article calls the determiner D and I called it Det.
- My display hides the lexical categories (V, Det, N, Name) because show()
  prints only the word at a leaf; the tree records them internally. The
  article's picture shows them.
- My NP for "john" goes through the Name category; the article's tree places
  the word under NP in its description, and I cannot see the picture to say
  whether it shows an intermediate category.

The article's tree is an image, so this comparison rests on its text
description.