Hi. I'm just starting to use python.
I am anxious about how best to set and access items one level down in a data structure if I am using __setitem__ and __getitem__.
At the moment I can do
for a data structure Data:
object.Data = { 'one' : [1, 2, {}, 4], 'two' : [5, 6, {}, 8]}
What is the goal of this data structure? I have a feeling this needs to be refactored...
However, if I wish to access object.Data['one'][0] for instance, I am using the following:
object['three'] = [0, 'val0'] # set x = object['three'][0] # get
Seems like you'd do much better with names for the items rather than an index. Maybe something like:
py> class Record(object):
... def __init__(self, foo, bar, dict, baz):
... self.foo = foo
... self.bar = bar
... self.dict = dict
... self.baz = baz
... def __repr__(self):
... return 'Record(%r, %r, %r, %r)' % (
... self.foo, self.bar, self.dict, self.baz)
...
py> data = dict(one=Record(1, 2, {}, 4),
... two=Record(5, 6, {}, 8))
py> data
{'two': Record(5, 6, {}, 8), 'one': Record(1, 2, {}, 4)}
py> data['one'].foo = 'val0'
py> data
{'two': Record(5, 6, {}, 8), 'one': Record('val0', 2, {}, 4)}
py> data['one'].foo
'val0'Is this advisable? I'm worried the syntax is very odd.
Yes it is odd. If you want to be more consistent with other Python syntax, but you don't want to use a Record, check for keys as tuples:
py> class C(object):
... def __init__(self):
... self.data = {}
... def __setitem__(self, x, value):
... try:
... name, index = x
... self.data.setdefault(name, {})[index] = value
... except ValueError:
... self.data[x] = value
... def __getitem__(self, x):
... try:
... name, index = x
... return self.data[name][index]
... except ValueError:
... return self.data[x]
...
py> c = C()
py> c.data
{}
py> c['one', 0] = 1
py> c['one', 3] = 4
py> c['two', 1] = 6
py> c['two', 2] = {}
py> c.data
{'two': {1: 6, 2: {}}, 'one': {0: 1, 3: 4}}
py>As you can see, Python has builin syntax support to allow tuples to be used as dict keys. (The parentheses can be omitted.)
Still, I think the class-based solution is much better than the __getitem__/__setitem__ one.
STeVe -- http://mail.python.org/mailman/listinfo/python-list
