[Tutor] when I create an instance of a class that inherits from Python dictionary, my data disappears
kent37 at tds.net
Sat Oct 7 14:46:07 CEST 2006
Bob Gailer wrote:
> tpc247 at gmail.com wrote:
>> hi all, I would like to create a class that specializes Python
>> dictionary. I would like an instance of this class to store objects
>> representing html form data, and I would like to have an instance of
>> this Data_Set class be able to use the Python dictionary method pop to
>> remove objects as I see fit. I defined the following:
>> class Data_Set(dict):
>> def __init__(self, dict_of_datum_objects, required=None):
>> self.keys = dict_of_datum_objects.keys
>> self.values = dict_of_datum_objects.values
>> self.required = required
>> For some reason, whenever I create an instance of this class with
>> data, all I get is an empty dictionary.
>> Am I doing something wrong ?
> Err, yes. You are assuming that assigning to self.keys and self.values
> creates dictionary entries. All that actually does is assign the 2 lists
> to 2 attributes.
> Try instead self.update(dict_of_datum_objects).
In general, when you create a subclass, the subclass __init__() method
should call the base class __init__(). Otherwise the base class is not
initialized. That is what you see - you get an empty dict.
The syntax for the call to the base class __init__() is a little
strange, it looks like this:
where base is the name of the base class and args are the arguments for
the base class __init__() method.
As Bob points out, you are also making unwarranted assumptions about the
way dict stores its data.
def __init__(self, dict_of_datum_objects, required=None):
self.required = required
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