Re: [Tutor] is it legal to have a class within a def
johnf [EMAIL PROTECTED] wrote def someMethod(): class MyClass(object): . if something: . return someval Did you try it? def f(): ... class C: pass ... return C ... def g(x): ... class C: pass ... if x == 42: ... return C ... else: return 666 ... c = f() c class __main__.C at 0x7ff1bbfc It works for me... -- Alan Gauld Author of the Learn to Program web site http://www.freenetpages.co.uk/hp/alan.gauld ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] is it legal to have a class within a def
bob gailer [EMAIL PROTECTED] wrote So the question becomes why would you want to do that? The main reason I could think of was to create a factory method for dynamically creating classes based on input parameters - for example currency convertors or similar. Equally you could change method implementations by passing lambdas etc. Useful in certain other languages but much less so in Python which allows dynamic changes to classes/objects after creation anyway. Alan G. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] is it legal to have a class within a def
johnf [EMAIL PROTECTED] wrote 1 and 3 are my reasons. I'm creating a Dabo app. When I attempted to create a special class that contained a dialog box I discovered that the dialog class created an indepentant type of window and allowed my program to continue running without waiting for the dialog to return a value first. Are you sure you made it a modal dialog? Any dialog will do that if it is opened modelessly, you need to use the modal version to make it block the app. Putting the class code in a functiion is legal but very inefficient and also prevents you from storing state etc in the dialog - you would need to reinitialise all valuues on each use. Thats OK if its simple but a lot of work(and slow) if its complex. HTH, -- Alan Gauld Author of the Learn to Program web site http://www.freenetpages.co.uk/hp/alan.gauld ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] is it legal to have a class within a def
On Thursday 03 January 2008 12:22:25 am Alan Gauld wrote: Are you sure you made it a modal dialog? Any dialog will do that if it is opened modelessly, you need to use the modal version to make it block the app. Yes. I believe the way I have coded the dialog causes a bug. If I create a static dialog and use showModal() it works as expected. Putting the class code in a functiion is legal but very inefficient and also prevents you from storing state etc in the dialog - you would need to reinitialise all valuues on each use. Thats OK if its simple but a lot of work(and slow) if its complex. I am creating a function that does a lookup of PK or FK fields. If the user does type in the correct identifier then the dialog does not appear and is not created. If the user types in a partial of the key then the dialog appears and the user picks from the list. The details of the dialog are dynamic for each call (based on some meta data) of the showModal(). So I started thinking why would I need the class outside of the function. If I instead used import class would I get a performance improvement? The function creates an instance each time it is required and then releases and closes. I am very interested in this possible difference between importing the class vs using the inline class. Any thoughts as what the difference is will help me understand Python a little better. -- John Fabiani ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] is it legal to have a class within a def
johnf [EMAIL PROTECTED] wrote If the user types in a partial of the key then the dialog appears and the user picks from the list. The details of the dialog are dynamic for each call (based on some meta data) of the showModal(). This might be a valid case for defining the class in the function since it could be that the number of fields, the labels etc change depending on the input values. That is exactly the kind of place where a local class makes sense. I am very interested in this possible difference between importing the class vs using the inline class. Any thoughts as what the difference is will help me understand Python a little better. There is no great secret, its just that by putting the class definition into the function you have to execute the definition each time you execute the function. If you put the class in a module and import it then the class definition is executed at import time and thats it. But if you need to change the definition each time you instantiate the dialog you will have a very complex init method so you might find it easier to redefine the class each time instead. -- Alan Gauld Author of the Learn to Program web site http://www.freenetpages.co.uk/hp/alan.gauld ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] is it legal to have a class within a def
On Thursday 03 January 2008 10:13:18 am Alan Gauld wrote:
johnf [EMAIL PROTECTED] wrote
If the user types in a partial of the key then the dialog
appears and the user picks from the list. The details of the dialog
are
dynamic for each call (based on some meta data) of the showModal().
This might be a valid case for defining the class in the function
since
it could be that the number of fields, the labels etc change depending
on the input values. That is exactly the kind of place where a local
class
makes sense.
I am very interested in this possible difference between importing
the class
vs using the inline class. Any thoughts as what the difference is
will help
me understand Python a little better.
There is no great secret, its just that by putting the class
definition
into the function you have to execute the definition each time you
execute the function. If you put the class in a module and import
it then the class definition is executed at import time and thats it.
But if you need to change the definition each time you instantiate the
dialog you will have a very complex init method so you might find
it easier to redefine the class each time instead.
Thanks for the response. Having only a short period using python under my
belt I find your type of help reassuring.
--
John Fabiani
___
Tutor maillist - Tutor@python.org
http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] is it legal to have a class within a def
johnf wrote: So I started thinking why would I need the class outside of the function. If I instead used import class would I get a performance improvement? The function creates an instance each time it is required and then releases and closes. I am very interested in this possible difference between importing the class vs using the inline class. There is another possibility which is probably what I would do - just define the class at global scope in the same module that uses it. Instead of def f(): class Z(object): pass # do something with Z write def f(): # do something with Z class Z(object): pass I.e. you don't have to put the class def'n in a separate module. Kent ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
[Tutor] is it legal to have a class within a def
def someMethod(): class MyClass(object): . if something: . return someval -- John Fabiani ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] is it legal to have a class within a def
johnf wrote: def someMethod(): class MyClass(object): . if something: . return someval Legal? Well the police won't come after you! Python allows a class statement anywhere. So this use is part of the language. So the question becomes why would you want to do that? Considerations: 1 - this usage creates a local object MyClass. The object will not be visible outside the function. The class definition is executed each time the function is called. 2 - the object could be returned or assigned to a global or added to a parameter that is a collection. 3 - if no instances are created in the function the object will disappear once the function execution ends. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] is it legal to have a class within a def
On Wednesday 02 January 2008 09:31:19 pm you wrote: johnf wrote: def someMethod(): class MyClass(object): . if something: . return someval Legal? Well the police won't come after you! That's a good thing! Python allows a class statement anywhere. So this use is part of the language. So the question becomes why would you want to do that? Considerations: 1 - this usage creates a local object MyClass. The object will not be visible outside the function. The class definition is executed each time the function is called. 2 - the object could be returned or assigned to a global or added to a parameter that is a collection. 3 - if no instances are created in the function the object will disappear once the function execution ends. 1 and 3 are my reasons. I'm creating a Dabo app. When I attempted to create a special class that contained a dialog box I discovered that the dialog class created an indepentant type of window and allowed my program to continue running without waiting for the dialog to return a value first. However, I noticed if I created the dialog within a function my program stopped and waited until the dialog was closed to continue. I think that I could define the Classes outside of the function and just import them when needed. But then I wanted a self contained function so I asked why not place the class code in the function? What is the difference? -- John Fabiani ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
