Re: Dictionaries and dot notation
Martin Drautzburg a écrit : > Daniel Nogradi wrote: > > > What if I want to create a datastructure that can be used in dot notation without having to create a class, i.e. because those objects have no behavior at all? >>> >>>A class inheriting from dict and implementing __getattr__ and >>>__setattr__ should do the trick... >> >> >>It can do the trick but one has to be careful with attributes that are >>used by dict such as update, keys, pop, etc. Actually it's noted in a >>comment at >>http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/361668 why the >>whole idea (attribute access of dictionaries) is a bad idea and I tend >>to agree. > > > Oh thank you. So all I have to do is have my object's class implement > __setattr__ and __getattr__, or derive it from a class that does so? > And I could save my "attributes" anywhere within my instance variables. > So I could even add a dictionary whose name does not conflict with what > python uses and whose key/value pairs hold the attributes I want to > access with dot notation and delegate all the python attributes to > their native positions? Oh I see, thats tricky. I still need to be > aware of the builtin stuff one way or the other. Yeps. FWIW, Daniel is right to raise a warning here, and I should have think one more minute before posting - since in fact in this case you don't care about dict-like behaviour. > Interesting. -- http://mail.python.org/mailman/listinfo/python-list
Re: Dictionaries and dot notation
On 2007-04-22, Martin Drautzburg <[EMAIL PROTECTED]> wrote: > Daniel Nogradi wrote: > > >>> > What if I want to create a datastructure that can be used in dot >>> > notation without having to create a class, i.e. because those >>> > objects have no behavior at all? >>> >>> A class inheriting from dict and implementing __getattr__ and >>> __setattr__ should do the trick... >> >> >> It can do the trick but one has to be careful with attributes that are >> used by dict such as update, keys, pop, etc. Actually it's noted in a >> comment at >> http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/361668 why the >> whole idea (attribute access of dictionaries) is a bad idea and I tend >> to agree. > > Oh thank you. So all I have to do is have my object's class implement > __setattr__ and __getattr__, or derive it from a class that does so? > And I could save my "attributes" anywhere within my instance variables. > So I could even add a dictionary whose name does not conflict with what > python uses and whose key/value pairs hold the attributes I want to > access with dot notation and delegate all the python attributes to > their native positions? Oh I see, thats tricky. I still need to be > aware of the builtin stuff one way or the other. Maybe you can do the opposite and create a class that implements __getitem__ and __setitem__ in function of attribute access. The following is an example: class Rec(object): def __init__(__, **kwargs): for key,value in kwargs.items(): setattr(__, key, value) def __getitem__(self, key): return getattr(self, key) def __setitem__ (self, key, val): setattr(self, key, val) rec = Rec(a=1) print rec.a print rec["a"] rec.b = 2 print rec["b"] rec["c"] = 3 print rec.c -- Antoon Pardon -- http://mail.python.org/mailman/listinfo/python-list
Re: Dictionaries and dot notation
En Mon, 23 Apr 2007 03:14:32 -0300, Martin Drautzburg <[EMAIL PROTECTED]> escribió: > I did not notice that I can use a single class (or a module) for > all my datastructures, because I can "plug in" new attributes into the > instance without the class knowing about them. > > I was mistaken to believe that I had to know about attributes at the > time of class creation. But your expample does not require that. Should > have read this more carefully. Welcome to Python and its dynamic nature! -- Gabriel Genellina -- http://mail.python.org/mailman/listinfo/python-list
Re: Dictionaries and dot notation
Alex Martelli wrote:
> Martin Drautzburg <[EMAIL PROTECTED]> wrote:
>
>> > mydata = data( )
>> > mydata.foo = 'foo'
>> > mydata.bar = 'bar'
>> >
>> > print mydata.foo
>> > print mydata.bar
>>
>> I am aware of all this.
>> Okay let me rephrase my question: is there a way of using dot
>> notation without having to create a class?
>
> Sure, all you need to create is an *INSTANCE* of a suitable type or
> class. For example:
>
d = dict(foo=23, bar=45)
m = new.module('for_martin')
m.__dict__.update(d)
m.foo
> 23
m.bar
> 45
>
> A module may be appropriate, since it's little more than a "wrapper
> around a dict to access items by dot notation":-).
Thanks, I finally got it. Even your previous example actually does the
trick. I did not notice that I can use a single class (or a module) for
all my datastructures, because I can "plug in" new attributes into the
instance without the class knowing about them.
I was mistaken to believe that I had to know about attributes at the
time of class creation. But your expample does not require that. Should
have read this more carefully.
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Re: Dictionaries and dot notation
Martin Drautzburg <[EMAIL PROTECTED]> wrote:
> > mydata = data( )
> > mydata.foo = 'foo'
> > mydata.bar = 'bar'
> >
> > print mydata.foo
> > print mydata.bar
>
> I am aware of all this.
> Okay let me rephrase my question: is there a way of using dot notation
> without having to create a class?
Sure, all you need to create is an *INSTANCE* of a suitable type or
class. For example:
>>> d = dict(foo=23, bar=45)
>>> m = new.module('for_martin')
>>> m.__dict__.update(d)
>>> m.foo
23
>>> m.bar
45
>>>
A module may be appropriate, since it's little more than a "wrapper
around a dict to access items by dot notation":-).
Alex
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Re: Dictionaries and dot notation
Martin Drautzburg <[EMAIL PROTECTED]> writes: > Okay let me rephrase my question: is there a way of using dot > notation without having to create a class? Dot notation, e.g. 'foo.bar', is parsed by the interpreter as "access the attribute named 'bar' of the object 'foo'". Objects have attributes either by virtue of the class having them, or the object getting them assigned after creation. Can you describe what you would change in the above, or can you re-word your request based on these facts? -- \ "Our products just aren't engineered for security." -- Brian | `\ Valentine, senior vice-president of Microsoft Windows | _o__) development | Ben Finney -- http://mail.python.org/mailman/listinfo/python-list
Re: Dictionaries and dot notation
Daniel Nogradi wrote: >> > What if I want to create a datastructure that can be used in dot >> > notation without having to create a class, i.e. because those >> > objects have no behavior at all? >> >> A class inheriting from dict and implementing __getattr__ and >> __setattr__ should do the trick... > > > It can do the trick but one has to be careful with attributes that are > used by dict such as update, keys, pop, etc. Actually it's noted in a > comment at > http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/361668 why the > whole idea (attribute access of dictionaries) is a bad idea and I tend > to agree. Oh thank you. So all I have to do is have my object's class implement __setattr__ and __getattr__, or derive it from a class that does so? And I could save my "attributes" anywhere within my instance variables. So I could even add a dictionary whose name does not conflict with what python uses and whose key/value pairs hold the attributes I want to access with dot notation and delegate all the python attributes to their native positions? Oh I see, thats tricky. I still need to be aware of the builtin stuff one way or the other. Interesting. -- http://mail.python.org/mailman/listinfo/python-list
Re: Dictionaries and dot notation
> mydata = data( ) > mydata.foo = 'foo' > mydata.bar = 'bar' > > print mydata.foo > print mydata.bar I am aware of all this. Okay let me rephrase my question: is there a way of using dot notation without having to create a class? -- http://mail.python.org/mailman/listinfo/python-list
Re: Dictionaries and dot notation
Martin Drautzburg a écrit :
> This may be pretty obvious for most of you:
>
> When I have an object (an instance of a class "Foo") I can access
> attributes via dot notation:
>
> aFoo.bar
>
> however when I have a dictionary
>
> aDict = {"bar":"something"}
>
> I have to write
>
> aDict["bar"]
>
> What if I want to create a datastructure that can be used in dot
> notation without having to create a class, i.e. because those objects
> have no behavior at all?
A class inheriting from dict and implementing __getattr__ and
__setattr__ should do the trick...
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Re: Dictionaries and dot notation
Bruno Desthuilliers a écrit :
> Martin Drautzburg a écrit :
>
>> This may be pretty obvious for most of you:
>>
>> When I have an object (an instance of a class "Foo") I can access
>> attributes via dot notation:
>>
>> aFoo.bar
>>
>> however when I have a dictionary
>> aDict = {"bar":"something"}
>>
>> I have to write
>>
>> aDict["bar"]
>>
>> What if I want to create a datastructure that can be used in dot
>> notation without having to create a class, i.e. because those objects
>> have no behavior at all?
>
>
> A class inheriting from dict and implementing __getattr__ and
> __setattr__ should do the trick...
Oh, yes, if you don't care about dict-like behaviour, you can also just:
class Data(object):
def __init__(self, **kw):
self.__dict__.update(kw)
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Re: Dictionaries and dot notation
> > This may be pretty obvious for most of you:
> >
> > When I have an object (an instance of a class "Foo") I can access
> > attributes via dot notation:
> >
> > aFoo.bar
> >
> > however when I have a dictionary
> >
> > aDict = {"bar":"something"}
> >
> > I have to write
> >
> > aDict["bar"]
> >
> > What if I want to create a datastructure that can be used in dot
> > notation without having to create a class, i.e. because those objects
> > have no behavior at all?
>
> A class inheriting from dict and implementing __getattr__ and
> __setattr__ should do the trick...
It can do the trick but one has to be careful with attributes that are
used by dict such as update, keys, pop, etc. Actually it's noted in a
comment at http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/361668
why the whole idea (attribute access of dictionaries) is a bad idea
and I tend to agree.
Daniel
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Re: Dictionaries and dot notation
> > This may be pretty obvious for most of you:
> >
> > When I have an object (an instance of a class "Foo") I can access
> > attributes via dot notation:
> >
> > aFoo.bar
> >
> > however when I have a dictionary
> >
> > aDict = {"bar":"something"}
> >
> > I have to write
> >
> > aDict["bar"]
> >
> > What if I want to create a datastructure that can be used in dot
> > notation without having to create a class, i.e. because those objects
> > have no behavior at all?
> >
> > I know that accessing an instance variable via bracket notation would
> > really have to be written as:
> >
> > aFoo.__dict__['bar']
> >
> > but this does not bring me any further, because I would still have to
> > plug in that __dict__ thing into my datastructure, which leads us to
> > the same question as above.
> >
> > Can anyone tell me what I am missing here?
What's wrong with creating a dummy class?
class data:
pass
mydata = data( )
mydata.foo = 'foo'
mydata.bar = 'bar'
print mydata.foo
print mydata.bar
Daniel
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Re: Dictionaries and dot notation
Martin Drautzburg wrote:
> This may be pretty obvious for most of you:
>
> When I have an object (an instance of a class "Foo") I can access
> attributes via dot notation:
>
> aFoo.bar
>
> however when I have a dictionary
>
> aDict = {"bar":"something"}
>
> I have to write
>
> aDict["bar"]
>
> What if I want to create a datastructure that can be used in dot
> notation without having to create a class, i.e. because those objects
> have no behavior at all?
>
> I know that accessing an instance variable via bracket notation would
> really have to be written as:
>
> aFoo.__dict__['bar']
>
> but this does not bring me any further, because I would still have to
> plug in that __dict__ thing into my datastructure, which leads us to
> the same question as above.
>
> Can anyone tell me what I am missing here?
This?
http://docs.python.org/ref/attribute-access.html
Stefan
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Dictionaries and dot notation
This may be pretty obvious for most of you:
When I have an object (an instance of a class "Foo") I can access
attributes via dot notation:
aFoo.bar
however when I have a dictionary
aDict = {"bar":"something"}
I have to write
aDict["bar"]
What if I want to create a datastructure that can be used in dot
notation without having to create a class, i.e. because those objects
have no behavior at all?
I know that accessing an instance variable via bracket notation would
really have to be written as:
aFoo.__dict__['bar']
but this does not bring me any further, because I would still have to
plug in that __dict__ thing into my datastructure, which leads us to
the same question as above.
Can anyone tell me what I am missing here?
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