On Fri, 25 Jul 2014 17:06:17 -0700, Bruce Whealton wrote:
> OK, Eclipse with PyDev doesn't like this first line, with the function:
> def add(self, (sub, pred, obj)):
In Python 2, you could include parenthesised parameters inside function
declarations as above. That is effectively a short cut for this version,
where you collect a single argument and then expand it into three
variables:
def add(self, sub_pred_obj):
sub, pred, obj = sub_pred_obj
In Python 3, that functionality was dropped and is no longer allowed. Now
you have to use the longer form.
[...]
> There are other places where I thought that there were too many
> parentheses and I tried removing one set of them. For example this
> snippet here:
>
> def remove(self, (sub, pred, obj)):
> """
> Remove a triple pattern from the graph. """
> triples = list(self.triples((sub, pred, obj)))
Firstly, the remove method expects to take a *single* argument (remember
that self is automatically provided by Python) which is then automatically
expanded into three variables sub, pred, obj. So you have to call it with a
list or tuple of three items (or even a string of length exactly 3).
Then, having split this list or tuple into three items, it then joins them
back again into a tuple:
(sub, pred, obj)
passes that tuple to the triples method:
self.triples((sub, pred, obj))
(not shown, but presumably it uses the same parenthesised parameter trick),
and then converts whatever triples returns into a list:
list(self.triples((sub, pred, obj)))
that list then being bound to the name "triples".
> Are the two sets parentheses needed after self.triples? That syntax is
> confusing to me. It seems that it should be triples =
> list(self.triples(sub, pred, obj))
It's needed because the triples method is written
def triples(self, (sub, pred, obj)):
instead of the more obvious:
def triples(self, sub, pred, obj):
--
Steven
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