Re: Making functions callable

[Anthony Hawkes]

Thanks Guys, especially Javier! I've spent so much time trawling Google for 
this info!

On Thursday, 27 March 2014 04:57:30 UTC+8, Anthony Hawkes wrote:
>
> Hi Guys,
>
> I'm running into a problem with django(I guess this would also affect 
> Python in general) where if I create a view eg
> def view(year=today.year())
> The year is never re-evaluated until the server is reloaded/restarted
>
> I'm trying to figure out how to make a callable method accessible as a 
> property if this is even possible to try and rectify this(not sure if this 
> is even the correct approach). I've had a look at some magic methods but 
> can't figure it out.
>
> Basically I want to make eg
>
> def year(something):
> return 'blah'
>
> Accessible using object.year as well as object.year()
>
> Any pointers/ideas etc?
>

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Re: Making functions callable

[Javier Guerra Giraldez]

On Wed, Mar 26, 2014 at 5:53 PM, Anthony  wrote:
> I've yet to test it but I read a few people stating to use lambdas
> variables/properties. Is it definitely the case that it will only evaluate
> once?


from the python docs (2.7):

Default parameter values are evaluated when the function definition is
executed. This means that the expression is evaluated once, when the
function is defined, and that the same “pre-computed” value is used
for each call. This is especially important to understand when a
default parameter is a mutable object, such as a list or a dictionary:
if the function modifies the object (e.g. by appending an item to a
list), the default value is in effect modified. This is generally not
what was intended. A way around this is to use None as the default,
and explicitly test for it in the body of the function.

-- 
Javier

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Re: Making functions callable

[John DeRosa]

Not sure what is going on without seeing the code. But something is None when 
it should be a string, as the exception is telling you.

It's often easiest to try out problem code interactively in Python, and zero in 
on the problem.

John


On Mar 26, 2014, at 3:53 PM, Anthony  wrote:

> Thanks John,
> 
> I've yet to test it but I read a few people stating to use lambdas 
> variables/properties. Is it definitely the case that it will only evaluate 
> once?
> 
> Either way I've embarked on the mission to make methods return as properties 
> and have found @property decorator to fit my needs, the issue was I was 
> calling Object.property not ObjectI().property, However I want to apply this 
> functionality to all my methods and am using:
> 
> __getattribute__
> 
> def __getattribute__(self, item):
> super(DateCalc, self).__getattribute__(item)
> 
> But I've run into the problem that my __init__ properties don't seem to be 
> initialised eg I get
> self._date_actual = datetime.strptime("{Y}-{m}-{d}".format(Y=year, m=month, 
> d=day), self._format_global).date() TypeError: must be string, not None
> 
> Anyone have an idea about what's going on?
> 
> 
> On Thu, Mar 27, 2014 at 5:07 AM, John DeRosa  wrote:
> For the default value to work as you expect, do this:
> 
> def view(request, year=None):
> if year is None:
> year = today.year()
> 
> 
> Kwarg defaults are evaluated when the module is interpreted for the first 
> time.
> 
> John
> 
> 
> On Mar 26, 2014, at 1:57 PM, Anthony Hawkes  wrote:
> 
>> Hi Guys,
>> 
>> I'm running into a problem with django(I guess this would also affect Python 
>> in general) where if I create a view eg
>> def view(year=today.year())
>> The year is never re-evaluated until the server is reloaded/restarted
>> 
>> I'm trying to figure out how to make a callable method accessible as a 
>> property if this is even possible to try and rectify this(not sure if this 
>> is even the correct approach). I've had a look at some magic methods but 
>> can't figure it out.
>> 
>> Basically I want to make eg
>> 
>> def year(something):
>> return 'blah'
>> 
>> Accessible using object.year as well as object.year()
>> 
>> Any pointers/ideas etc?
>> 
>> -- 
>> You received this message because you are subscribed to the Google Groups 
>> "Django users" group.
>> To unsubscribe from this group and stop receiving emails from it, send an 
>> email to django-users+unsubscr...@googlegroups.com.
>> 
>> To post to this group, send email to django-users@googlegroups.com.
>> Visit this group at http://groups.google.com/group/django-users.
>> To view this discussion on the web visit 
>> https://groups.google.com/d/msgid/django-users/e7adace8-ffc9-4f77-b970-e73bed5ae8e1%40googlegroups.com.
>> For more options, visit https://groups.google.com/d/optout.
> 
> 
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> 
> 
> 
> -- 
> Anthony Hawkes
> E-Mail: lifesillus...@gmail.com
> Ph: 0400 372 260
> 
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Re: Making functions callable

[Mike Dewhirst]

On 27/03/2014 7:57am, Anthony Hawkes wrote:

Hi Guys,

I'm running into a problem with django(I guess this would also affect
Python in general) where if I create a view eg
def view(year=today.year())
The year is never re-evaluated until the server is reloaded/restarted

I'm trying to figure out how to make a callable method accessible as a
property if this is even possible to try and rectify this(not sure if
this is even the correct approach). I've had a look at some magic
methods but can't figure it out.

Basically I want to make eg

def year(something):
 return 'blah'


You should be able to pass the callable as an argument. It then gets 
evaluated each time it is called ...


Here is one I use ... from time to time :)

def when():
return datetime.now(tz=pytz.utc)




Accessible using object.year as well as object.year()

Any pointers/ideas etc?

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Re: Making functions callable

[Anthony]

Thanks John,

I've yet to test it but I read a few people stating to use lambdas
variables/properties. Is it definitely the case that it will only evaluate
once?

Either way I've embarked on the mission to make methods return as
properties and have found @property decorator to fit my needs, the issue
was I was calling Object.property not ObjectI().property, However I want to
apply this functionality to all my methods and am using:

__getattribute__

def __getattribute__(self, item):
super(DateCalc, self).__getattribute__(item)

But I've run into the problem that my __init__ properties don't seem to be
initialised eg I get
self._date_actual = datetime.strptime("{Y}-{m}-{d}".format(Y=year, m=month,
d=day), self._format_global).date() TypeError: must be string, not None

Anyone have an idea about what's going on?


On Thu, Mar 27, 2014 at 5:07 AM, John DeRosa  wrote:

> For the default value to work as you expect, do this:
>
> def view(request, year=None):
> if year is None:
> year = today.year()
>
>
> Kwarg defaults are evaluated when the module is interpreted for the first
> time.
>
> John
>
>
> On Mar 26, 2014, at 1:57 PM, Anthony Hawkes 
> wrote:
>
> Hi Guys,
>
> I'm running into a problem with django(I guess this would also affect
> Python in general) where if I create a view eg
> def view(year=today.year())
> The year is never re-evaluated until the server is reloaded/restarted
>
> I'm trying to figure out how to make a callable method accessible as a
> property if this is even possible to try and rectify this(not sure if this
> is even the correct approach). I've had a look at some magic methods but
> can't figure it out.
>
> Basically I want to make eg
>
> def year(something):
> return 'blah'
>
> Accessible using object.year as well as object.year()
>
> Any pointers/ideas etc?
>
> --
> You received this message because you are subscribed to the Google Groups
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> .
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>
>
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>
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>



-- 
Anthony Hawkes
E-Mail: lifesillus...@gmail.com
Ph: 0400 372 260

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Re: Making functions callable

[John DeRosa]

For the default value to work as you expect, do this:

def view(request, year=None):
if year is None:
year = today.year()


Kwarg defaults are evaluated when the module is interpreted for the first time.

John


On Mar 26, 2014, at 1:57 PM, Anthony Hawkes  wrote:

> Hi Guys,
> 
> I'm running into a problem with django(I guess this would also affect Python 
> in general) where if I create a view eg
> def view(year=today.year())
> The year is never re-evaluated until the server is reloaded/restarted
> 
> I'm trying to figure out how to make a callable method accessible as a 
> property if this is even possible to try and rectify this(not sure if this is 
> even the correct approach). I've had a look at some magic methods but can't 
> figure it out.
> 
> Basically I want to make eg
> 
> def year(something):
> return 'blah'
> 
> Accessible using object.year as well as object.year()
> 
> Any pointers/ideas etc?
> 
> -- 
> You received this message because you are subscribed to the Google Groups 
> "Django users" group.
> To unsubscribe from this group and stop receiving emails from it, send an 
> email to django-users+unsubscr...@googlegroups.com.
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Making functions callable

[Anthony Hawkes]

Hi Guys,

I'm running into a problem with django(I guess this would also affect 
Python in general) where if I create a view eg
def view(year=today.year())
The year is never re-evaluated until the server is reloaded/restarted

I'm trying to figure out how to make a callable method accessible as a 
property if this is even possible to try and rectify this(not sure if this 
is even the correct approach). I've had a look at some magic methods but 
can't figure it out.

Basically I want to make eg

def year(something):
return 'blah'

Accessible using object.year as well as object.year()

Any pointers/ideas etc?

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