Implement discard and remove function

[pymia]

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[pymia]

I signed it!

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[googlebot]

CLAs look good, thanks!

[mina86]

This also needs tests and documentation. And some good documentation because semantics of removing elements from a prefix set aren’t obvious. For example, what should be the result of the following:

ps = pygtrie.PrefixSet(factory=pygtrie.StringTrie)
ps.add('foo/bar/baz')
assert 'foo/bar/baz/qux' in ps
ps.remove('foo/bar/baz/qux')  # Should it throw?
'foo/bar/baz/qux' in ps  # Is this True?

[mina86]

Clearly, this pass should be return, no?

[mina86]

Uh? Why are you catching the exception? It should be propagated.

More importantly, why are you duplicating the implementation? It’s much better to implement discard in terms of remove, i.e.:

    def remove(self, key):
        …

    def discard(self, key):
        try:
            self.remove(key)
        except KeyError:
            pass

[mina86]

I don’t understand why you have this special case. node.children = {} is enough to remove all the children, you don’t have to iterate over them.

[mina86]

This leaves out empty nodes which don’t lead to anything. For example, if you first add foo/bar/baz you get a prefix set with three nodes:

foo → bar → baz

Only baz’s value is set. If you now remove foo/bar you end up with an empty set which nonetheless has two nodes:

foo → bar