Beginning Python - From Novice to Professional

CHAPTER 6 ■ ABSTRACTION 123
(5, 6, 7)
{'foo': 1, 'bar': 2}
>>> print_params_4(1, 2)
1 2 3
()
{}
By combining all these techniques, you can do quite a lot. If you wonder how some combination
might work (or whether it’s allowed), just try it! (In the next section, you see how * and
** can be used at the point of call as well, regardless of whether they were used in the function
definition.)
Now, back to the original problem: how you can use this in the name-storing example.
The solution is shown here:
def store(data, *full_names):
for full_name in full_names:
names = full_name.split()
if len(names) == 2: names.insert(1, '')
labels = 'first', 'middle', 'last'
for label, name in zip(labels, names):
people = lookup(data, label, name)
if people:
people.append(full_name)
else:
data[label][name] = [full_name]
Using this function is just as easy as using the previous version, which only accepted
one name:
>>> d = {}
>>> init(d)
>>> store(d, 'Han Solo')
But now you can also do this:
>>> store(d, 'Luke Skywalker', 'Anakin Skywalker')
>>> lookup(d, 'last', 'Skywalker')
['Luke Skywalker', 'Anakin Skywalker']
Reversing the Process
Now you’ve learned about gathering up parameters in tuples and dictionaries, but it is in fact
possible to do the “opposite” as well, with the same two operators, * and **. What might the
opposite of parameter gathering be? Let’s say we have the following function available:
def add(x, y): return x + y
■Note You can find a more efficient version of this function in the operator module.