Re: beginner, idomatic python 2
bambam a écrit : > "Bruno Desthuilliers" <[EMAIL PROTECTED]> > wrote in message news:[EMAIL PROTECTED] >> As a side note, in Python, inheritance ... >> ... should usually not be used for typing. > > :~( > I'm sorry, I don't even know what that means... The code I > have inherited from someone only a little more knowledgeable > than me, and is still full of development artifacts anyway. > > The Pwr and Psp classes inherit from the Device class not > neccessarily because that is a Good Thing, more because > the development process led to them being thought of that > way. All devices have a mixture of common and differing > attributes. > > What is 'typing'? > Mmm... Most CS experts don't really agree on this, and I'm certainly not one (expert). So I won't even try to explain it by myself, and let you google for "type system", "static typing", "dynamic typing", "duck typing" etc... Now what I meant here is that in Python, you don't have to make class B inherit from class A to let you use an instance of B where an instance of A was expected - all you need is that both objects share the set of attributes and methods you're going to use. Inheritence is only useful for sharing common code. HTH -- http://mail.python.org/mailman/listinfo/python-list
Re: beginner, idomatic python 2
On 2007-08-31, bambam <[EMAIL PROTECTED]> wrote: > "Bruno Desthuilliers" > <[EMAIL PROTECTED]> wrote in > message news:[EMAIL PROTECTED] >> As a side note, in Python, inheritance ... ... should usually >> not be used for typing. > >:~( > I'm sorry, I don't even know what that means... The code I have > inherited from someone only a little more knowledgeable than > me, and is still full of development artifacts anyway. > > The Pwr and Psp classes inherit from the Device class not > neccessarily because that is a Good Thing, more because the > development process led to them being thought of that way. All > devices have a mixture of common and differing attributes. > > What is 'typing'? In a language with strict types, you may need to make a set of classes all inherit from one base class simply in order to get the code to compile. A common example is a set of classes that all behave like file streams. You don't need to do this in Python. Simply have the object provide the right methods and you are done. -- Neil Cerutti -- http://mail.python.org/mailman/listinfo/python-list
Re: beginner, idomatic python 2
"Bruno Desthuilliers" <[EMAIL PROTECTED]> wrote in message news:[EMAIL PROTECTED] > > As a side note, in Python, inheritance ... > ... should usually not be used for typing. :~( I'm sorry, I don't even know what that means... The code I have inherited from someone only a little more knowledgeable than me, and is still full of development artifacts anyway. The Pwr and Psp classes inherit from the Device class not neccessarily because that is a Good Thing, more because the development process led to them being thought of that way. All devices have a mixture of common and differing attributes. What is 'typing'? Steve. -- http://mail.python.org/mailman/listinfo/python-list
Re: beginner, idomatic python 2
Thank you. I'm glad to see that I don't need to choose between two opposing viewpoints :~) Steve. -- http://mail.python.org/mailman/listinfo/python-list
Re: beginner, idomatic python 2
bambam a écrit :
Steve, could you please stop top-posting ?-) TIA
> "Dan Bishop" <[EMAIL PROTECTED]> wrote in message
> news:[EMAIL PROTECTED]
>> On Aug 23, 10:21 pm, "bambam" <[EMAIL PROTECTED]> wrote:
>>> Would someone like to suggest a replacement for this? This is a
>>> function that returns different kinds of similar objects, depending
>>> on what is asked for. PSP and PWR are classes. I don't really
>>> want to re-write the calling code very much: I'm just wondering
>>> if the function can be replaced with some kind of OOP pattern.
>>>
>>> def Device(DeviceType):
>>> if DeviceType=='PSP':
>>> return PSP()
>>> elif DeviceType=="Power Supply"
>>> return PWR()
>>> etc...
>>>
>>> Thanks!
>> Typically, you'd use a dictionary:
>>
>> DEVICE_DICT = {
>>'PSP': PSP.
>>'Power Supply': PWR,
>># etc.
>> }
>>
>> and your function would simply return DEVICE_DICT[device_type]()
>>
> Thank you. I didn't reply earlier because I was trying to get my
> head around what you wrote, which was strange and foreign
> to me.
>
> It seems to me that the dictionary object you suggested is a
> direct replacement for the function code,
Almost, yes !-)
> only more efficient
> because the case table is internalised with a hash table, and
> the original if/elif/else case table was unlikely to be implemented
> as a hash table.
>
> And presumably, it is idiomatic
It is. Dicts are probably the central data structure in Python, and are
highly optimised. You'll find quite a lot of dict-based dispatch in
Python code.
> because Python programmers
> expect to use dictionaries for their lookup tables.
Indeed - that's what dictionnaries are for.
> You have answered a question I didn't know enough to ask :~)
> --which is why I started with the general question, so I don't
> feel too stupid about that --.
>
> And now I wonder about the 'other' question. Should I consider
> dynamically overriding the methods in my 'Device' class, instead
> of creating separate classes for the Psp and Pwr devices?
> I could create an object of the base Device class, and at init
> I could make sure the methods were connected for a Psp or
> a Pwr device. When (if ever) is that a good idea?
While it's technically possible, I wouldn't advise such a design (which
looks pretty close to the Prototype pattern) unless you need to have
something *highly* extensible and customisable (and even then, there are
other - possibly better - ways, depending on the context). If the Device
taxonomy is stable and well defined, you're certainly
DoingTheSimplestThing (here, a dict-based dispatch encapsulated in a
factory function...).
As a side note, in Python, inheritance is mostly an implementation
detail, and should usually not be used for typing.
My 2 cents...
--
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Re: beginner, idomatic python 2
bambam wrote:
[but he top-posted]
> "Dan Bishop" <[EMAIL PROTECTED]> wrote in message
> news:[EMAIL PROTECTED]
>> On Aug 23, 10:21 pm, "bambam" <[EMAIL PROTECTED]> wrote:
>>> Would someone like to suggest a replacement for this? This is a
>>> function that returns different kinds of similar objects, depending
>>> on what is asked for. PSP and PWR are classes. I don't really
>>> want to re-write the calling code very much: I'm just wondering
>>> if the function can be replaced with some kind of OOP pattern.
>>>
>>> def Device(DeviceType):
>>> if DeviceType=='PSP':
>>> return PSP()
>>> elif DeviceType=="Power Supply"
>>> return PWR()
>>> etc...
>>>
>>> Thanks!
>> Typically, you'd use a dictionary:
>>
>> DEVICE_DICT = {
>>'PSP': PSP.
>>'Power Supply': PWR,
>># etc.
>> }
>>
>> and your function would simply return DEVICE_DICT[device_type]()
>>
> Thank you. I didn't reply earlier because I was trying to get my
> head around what you wrote, which was strange and foreign
> to me.
>
> It seems to me that the dictionary object you suggested is a
> direct replacement for the function code, only more efficient
> because the case table is internalised with a hash table, and
> the original if/elif/else case table was unlikely to be implemented
> as a hash table.
>
> And presumably, it is idiomatic because Python programmers
> expect to use dictionaries for their lookup tables.
>
> You have answered a question I didn't know enough to ask :~)
> --which is why I started with the general question, so I don't
> feel too stupid about that --.
>
> And now I wonder about the 'other' question. Should I consider
> dynamically overriding the methods in my 'Device' class, instead
> of creating separate classes for the Psp and Pwr devices?
> I could create an object of the base Device class, and at init
> I could make sure the methods were connected for a Psp or
> a Pwr device. When (if ever) is that a good idea?
>
The fact that it's technically possible in Python doesn't mean it's
always a good idea. I prefer to reserve that kind of behavior for when
the effective behavior of an object needs to change after it's been
created. Here you know at creation time which type you want, so it makes
sense to me to create exactly that kind of object. Otherwise you are
obscuring your program's structure by using dynamic type modification
unnecessarily.
Just my $0.02, others will have different opinions.
regards
Steve
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Re: beginner, idomatic python 2
Thank you. I didn't reply earlier because I was trying to get my
head around what you wrote, which was strange and foreign
to me.
It seems to me that the dictionary object you suggested is a
direct replacement for the function code, only more efficient
because the case table is internalised with a hash table, and
the original if/elif/else case table was unlikely to be implemented
as a hash table.
And presumably, it is idiomatic because Python programmers
expect to use dictionaries for their lookup tables.
You have answered a question I didn't know enough to ask :~)
--which is why I started with the general question, so I don't
feel too stupid about that --.
And now I wonder about the 'other' question. Should I consider
dynamically overriding the methods in my 'Device' class, instead
of creating separate classes for the Psp and Pwr devices?
I could create an object of the base Device class, and at init
I could make sure the methods were connected for a Psp or
a Pwr device. When (if ever) is that a good idea?
Steve.
"Dan Bishop" <[EMAIL PROTECTED]> wrote in message
news:[EMAIL PROTECTED]
> On Aug 23, 10:21 pm, "bambam" <[EMAIL PROTECTED]> wrote:
>> Would someone like to suggest a replacement for this? This is a
>> function that returns different kinds of similar objects, depending
>> on what is asked for. PSP and PWR are classes. I don't really
>> want to re-write the calling code very much: I'm just wondering
>> if the function can be replaced with some kind of OOP pattern.
>>
>> def Device(DeviceType):
>> if DeviceType=='PSP':
>> return PSP()
>> elif DeviceType=="Power Supply"
>> return PWR()
>> etc...
>>
>> Thanks!
>
> Typically, you'd use a dictionary:
>
> DEVICE_DICT = {
>'PSP': PSP.
>'Power Supply': PWR,
># etc.
> }
>
> and your function would simply return DEVICE_DICT[device_type]()
>
--
http://mail.python.org/mailman/listinfo/python-list
Re: beginner, idomatic python 2
bambam a écrit :
>> trying to be "idiomatic"
>
> ...I hope that if a python programmer looks at my code it
> won't be an excuse to discard it.
Hopefully not - and nothing forces you into adopting the common
convention !-) But it's a fact that Python relies heavily on naming
conventions, and that it greatly helps readability.
> Less of an issue with Python
> than with C/C++, but since I'm just starting...
>
> def device(DeviceType):
> if DeviceType=='PSP':
> return Psp()
> elif DeviceType=="Power Supply"
> return Pwr()
>
> What about the parameter "DeviceType"?
DEVICE_TYPES = {
'PSP' : Psp,
'Power Supply' : Pwr,
}
def get_device(device_type):
cls = DEVICE_TYPES.get(device_type, None)
if cls is not None:
return cls()
# implicitly returns None, which may or not be a GoodThing(tm)
HTH
--
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Re: beginner, idomatic python 2
> trying to be "idiomatic" ...I hope that if a python programmer looks at my code it won't be an excuse to discard it. Less of an issue with Python than with C/C++, but since I'm just starting... def device(DeviceType): if DeviceType=='PSP': return Psp() elif DeviceType=="Power Supply" return Pwr() What about the parameter "DeviceType"? Also, I see what you mean now, DEVICE_DICT is upper case because it is a 'constant' -- I'd missed that point. Steve. "Bruno Desthuilliers" <[EMAIL PROTECTED]> wrote in message news:[EMAIL PROTECTED] > bambam a écrit : >> Would someone like to suggest a replacement for this? This is a >> function that returns different kinds of similar objects, depending >> on what is asked for. PSP and PWR are classes. I don't really >> want to re-write the calling code very much: I'm just wondering >> if the function can be replaced with some kind of OOP pattern. > > Dan already answered to this. Just as a side note, and since you're trying > to be "idiomatic", Python's naming convention is to use all_lower for > functions, MixedCaps for classes (except - mostly for historical reasons - > the builtin types...), and ALL_LOWER for symbolic (pseudo) constants. > > >> def Device(DeviceType): >> if DeviceType=='PSP': >> return PSP() >> elif DeviceType=="Power Supply" >> return PWR() >> etc... >> >> >> Thanks! -- http://mail.python.org/mailman/listinfo/python-list
Re: beginner, idomatic python 2
Bruno Desthuilliers a écrit : (snip) > and ALL_LOWER That's 'ALL_UPPER', of course :( > for symbolic (pseudo) > constants. > -- http://mail.python.org/mailman/listinfo/python-list
Re: beginner, idomatic python 2
bambam a écrit : > Would someone like to suggest a replacement for this? This is a > function that returns different kinds of similar objects, depending > on what is asked for. PSP and PWR are classes. I don't really > want to re-write the calling code very much: I'm just wondering > if the function can be replaced with some kind of OOP pattern. Dan already answered to this. Just as a side note, and since you're trying to be "idiomatic", Python's naming convention is to use all_lower for functions, MixedCaps for classes (except - mostly for historical reasons - the builtin types...), and ALL_LOWER for symbolic (pseudo) constants. > def Device(DeviceType): > if DeviceType=='PSP': > return PSP() > elif DeviceType=="Power Supply" > return PWR() > etc... > > > Thanks! > > -- http://mail.python.org/mailman/listinfo/python-list
Re: beginner, idomatic python 2
On Aug 23, 10:21 pm, "bambam" <[EMAIL PROTECTED]> wrote:
> Would someone like to suggest a replacement for this? This is a
> function that returns different kinds of similar objects, depending
> on what is asked for. PSP and PWR are classes. I don't really
> want to re-write the calling code very much: I'm just wondering
> if the function can be replaced with some kind of OOP pattern.
>
> def Device(DeviceType):
> if DeviceType=='PSP':
> return PSP()
> elif DeviceType=="Power Supply"
> return PWR()
> etc...
>
> Thanks!
Typically, you'd use a dictionary:
DEVICE_DICT = {
'PSP': PSP.
'Power Supply': PWR,
# etc.
}
and your function would simply return DEVICE_DICT[device_type]()
--
http://mail.python.org/mailman/listinfo/python-list
beginner, idomatic python 2
Would someone like to suggest a replacement for this? This is a function that returns different kinds of similar objects, depending on what is asked for. PSP and PWR are classes. I don't really want to re-write the calling code very much: I'm just wondering if the function can be replaced with some kind of OOP pattern. def Device(DeviceType): if DeviceType=='PSP': return PSP() elif DeviceType=="Power Supply" return PWR() etc... Thanks! -- http://mail.python.org/mailman/listinfo/python-list
