Re: using forloop.counter to access data

[Andre Terra]

You could always try writing a custom template tag or filter as someone
else suggested earlier in the thread before resorting to JavaScript.

Cheers,
AT
On Mar 21, 2012 5:41 PM, "Larry Martell"  wrote:

> On Wed, Mar 21, 2012 at 12:52 PM, James  wrote:
> >
> >
> > On Wednesday, March 21, 2012 10:41:08 AM UTC-4, Larry@gmail.comwrote:
> >>
> >> On Wed, Mar 21, 2012 at 7:53 AM, James <> wrote:
> >> >
> >> >
> >> > On Wednesday, March 21, 2012 8:47:23 AM UTC-4, larry@gmail.com
> >> > wrote:
> >> >>
> >> >> This is probably a stupid newbie question 
> >> >>
> >> >> I want to access a column of data in a row using forloop.counter, but
> >> >> I cannot get it to work.
> >> >>
> >> >> In my test code, if I display {{ forloop.counter }} I get 2
> >> >> If I display {{ headers.0.2 }} I get ToolType
> >> >> But if I display {{ headers.0.forloop.counter }} I get nothing
> >> >>
> >> >> What is the proper syntax for this?
> >> >
> >> >
> >> > the forloop.counter and friends will simply give you information about
> >> > the
> >> > iteration, it won't give you any information about the data in the
> >> > queryset
> >>
> >> Yes, I realize that. I am using it withing a loop to try an access a
> >> specific item of data. The code I showed was just an example from one
> >> iteration of the loop.
> >>
> >> > (I'm assuming this is what you mean when you say column).
> >> >
> >> > Here are the
> >> >
> >> > docs
> https://docs.djangoproject.com/en/dev/ref/templates/builtins/?from=olddocs#for
> >> >
> >> >  If you want to access the column of data, assuming it's referenced
> from
> >> > a
> >> > model, just the attribute of that model. If you passed in a list to
> the
> >> > template, you just use the django "dot" look-up syntax.
> >>
> >> Perhaps my question wasn't clear. I have a list called headers. From
> >> within a for loop I want the n'th item from the first row. In the loop
> >> I am trying to access {{ headers.0.forloop.counter }} but I get no
> >> value from that. But if I hard code the number (as a test), e.g.:  {{
> >> headers.0.2 }} then I do get the value.
> >
> >  With regards to your reply:
> >
> >
> >>  Yes, I realize that. I am using it withing a loop to try an access a
> >> specific item of data. The code I showed was just an example from one
> >> iteration of the loop.
> >
> >
> > You can't use forloop and friends in the manner you attempting to use it.
> > It's The reason is, headers.0 has no attribute named "forloop"
> >
> > The best that you could do here, in this situation, is to create a custom
> > filter and pass it forloop.counter as variable like so:
> > {{ headers.0|forloop.counter }} You will of course have to write that
> filter
> > out first, register it, and install it in the template.
> >
> > I'm still not sure if this is the right approach. Why not just iterate
> over
> > the list itself, if you want to print the nth item within the list?
>
> That would be really inefficient, as the table can have thousands of
> rows, with 30 columns each. I'd have to iterate through the header row
> for each column in each row to get the value to put into the href.
>
> > Or,
> > structure the list/queryset from the view such that you don't have to do
> > such acrobatics.
> >
> >>  But if I hard code the number (as a test), e.g.:  {{
> >> headers.0.2 }} then I do get the value.
> >
> >
> > This works because headers.0 has an attribute that works by way of the
> > django dot look up. See Tom Evan's post regarding this.
> >
> > It seems to me that you have a list of lists (and not a single list). In
> > which case, you can just iterate over the first list and iterate over the
> > second list. If you need some control flow, just use the standard if /
> else
> > conditions. But, maybe I'm missing something?
>
> Yes, I think you are. I have 2 header rows, and thousands of data
> rows. For each column in each data row I have to construct a href. One
> of the parameters in the href comes from the first header row. The
> header rows get processed first, then the data rows (to build the
> table). So by the time I am processing the data I don't have the
> header any more. I should probably just do this in javascript.
>
> > Even easier would be to use django's introspect feature and create models
> > based on the tables in the DB, query the DB using the models and create
> > querysets. Then you can access and display the data in a more
> > coherent manner.
> >
> > see the docs here for
> > introspection:
> https://docs.djangoproject.com/en/dev/howto/legacy-databases/?from=olddocs
>
>
> That already is the case. I am trying to add functionality to an existing
> app.
>
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Re: using forloop.counter to access data

[Larry Martell]

On Wed, Mar 21, 2012 at 12:52 PM, James  wrote:
>
>
> On Wednesday, March 21, 2012 10:41:08 AM UTC-4, larry@gmail.com wrote:
>>
>> On Wed, Mar 21, 2012 at 7:53 AM, James <> wrote:
>> >
>> >
>> > On Wednesday, March 21, 2012 8:47:23 AM UTC-4, larry@gmail.com
>> > wrote:
>> >>
>> >> This is probably a stupid newbie question 
>> >>
>> >> I want to access a column of data in a row using forloop.counter, but
>> >> I cannot get it to work.
>> >>
>> >> In my test code, if I display {{ forloop.counter }} I get 2
>> >> If I display {{ headers.0.2 }} I get ToolType
>> >> But if I display {{ headers.0.forloop.counter }} I get nothing
>> >>
>> >> What is the proper syntax for this?
>> >
>> >
>> > the forloop.counter and friends will simply give you information about
>> > the
>> > iteration, it won't give you any information about the data in the
>> > queryset
>>
>> Yes, I realize that. I am using it withing a loop to try an access a
>> specific item of data. The code I showed was just an example from one
>> iteration of the loop.
>>
>> > (I'm assuming this is what you mean when you say column).
>> >
>> > Here are the
>> >
>> > docs https://docs.djangoproject.com/en/dev/ref/templates/builtins/?from=olddocs#for
>> >
>> >  If you want to access the column of data, assuming it's referenced from
>> > a
>> > model, just the attribute of that model. If you passed in a list to the
>> > template, you just use the django "dot" look-up syntax.
>>
>> Perhaps my question wasn't clear. I have a list called headers. From
>> within a for loop I want the n'th item from the first row. In the loop
>> I am trying to access {{ headers.0.forloop.counter }} but I get no
>> value from that. But if I hard code the number (as a test), e.g.:  {{
>> headers.0.2 }} then I do get the value.
>
>  With regards to your reply:
>
>
>>  Yes, I realize that. I am using it withing a loop to try an access a
>> specific item of data. The code I showed was just an example from one
>> iteration of the loop.
>
>
> You can't use forloop and friends in the manner you attempting to use it.
> It's The reason is, headers.0 has no attribute named "forloop"
>
> The best that you could do here, in this situation, is to create a custom
> filter and pass it forloop.counter as variable like so:
> {{ headers.0|forloop.counter }} You will of course have to write that filter
> out first, register it, and install it in the template.
>
> I'm still not sure if this is the right approach. Why not just iterate over
> the list itself, if you want to print the nth item within the list?

That would be really inefficient, as the table can have thousands of
rows, with 30 columns each. I'd have to iterate through the header row
for each column in each row to get the value to put into the href.

> Or,
> structure the list/queryset from the view such that you don't have to do
> such acrobatics.
>
>>  But if I hard code the number (as a test), e.g.:  {{
>> headers.0.2 }} then I do get the value.
>
>
> This works because headers.0 has an attribute that works by way of the
> django dot look up. See Tom Evan's post regarding this.
>
> It seems to me that you have a list of lists (and not a single list). In
> which case, you can just iterate over the first list and iterate over the
> second list. If you need some control flow, just use the standard if / else
> conditions. But, maybe I'm missing something?

Yes, I think you are. I have 2 header rows, and thousands of data
rows. For each column in each data row I have to construct a href. One
of the parameters in the href comes from the first header row. The
header rows get processed first, then the data rows (to build the
table). So by the time I am processing the data I don't have the
header any more. I should probably just do this in javascript.

> Even easier would be to use django's introspect feature and create models
> based on the tables in the DB, query the DB using the models and create
> querysets. Then you can access and display the data in a more
> coherent manner.
>
> see the docs here for
> introspection: https://docs.djangoproject.com/en/dev/howto/legacy-databases/?from=olddocs


That already is the case. I am trying to add functionality to an existing app.

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Re: using forloop.counter to access data

[James]

On Wednesday, March 21, 2012 10:41:08 AM UTC-4, larry@gmail.com wrote:
>
> On Wed, Mar 21, 2012 at 7:53 AM, James <> wrote:
> >
> >
> > On Wednesday, March 21, 2012 8:47:23 AM UTC-4, Larry@gmail.comwrote:
> >>
> >> This is probably a stupid newbie question 
> >>
> >> I want to access a column of data in a row using forloop.counter, but
> >> I cannot get it to work.
> >>
> >> In my test code, if I display {{ forloop.counter }} I get 2
> >> If I display {{ headers.0.2 }} I get ToolType
> >> But if I display {{ headers.0.forloop.counter }} I get nothing
> >>
> >> What is the proper syntax for this?
> >
> >
> > the forloop.counter and friends will simply give you information about 
> the
> > iteration, it won't give you any information about the data in the 
> queryset
>
> Yes, I realize that. I am using it withing a loop to try an access a
> specific item of data. The code I showed was just an example from one
> iteration of the loop.
>
> > (I'm assuming this is what you mean when you say column).
> >
> > Here are the
> > docs 
> https://docs.djangoproject.com/en/dev/ref/templates/builtins/?from=olddocs#for
> >
> >  If you want to access the column of data, assuming it's referenced from 
> a
> > model, just the attribute of that model. If you passed in a list to the
> > template, you just use the django "dot" look-up syntax.
>
> Perhaps my question wasn't clear. I have a list called headers. From
> within a for loop I want the n'th item from the first row. In the loop
> I am trying to access {{ headers.0.forloop.counter }} but I get no
> value from that. But if I hard code the number (as a test), e.g.:  {{
> headers.0.2 }} then I do get the value.
>
 With regards to your reply:


 Yes, I realize that. I am using it withing a loop to try an access a
> specific item of data. The code I showed was just an example from one
> iteration of the loop.


You can't use forloop and friends in the manner you attempting to use it. 
It's The reason is, headers.0 has no attribute named "forloop"

The best that you could do here, in this situation, is to create a custom 
filter and pass it forloop.counter as variable like so:
{{ headers.0|forloop.counter }} You will of course have to write that 
filter out first, register it, and install it in the template.

I'm still not sure if this is the right approach. Why not just iterate over 
the list itself, if you want to print the nth item within the list? Or, 
structure the list/queryset from the view such that you don't have to do 
such acrobatics.

 But if I hard code the number (as a test), e.g.:  {{
> headers.0.2 }} then I do get the value. 


This works because headers.0 has an attribute that works by way of the 
django dot look up. See Tom Evan's post regarding this.

It seems to me that you have a list of lists (and not a single list). In 
which case, you can just iterate over the first list and iterate over the 
second list. If you need some control flow, just use the standard if / else 
conditions. But, maybe I'm missing something?

Even easier would be to use django's introspect feature and create models 
based on the tables in the DB, query the DB using the models and create 
querysets. Then you can access and display the data in a more 
coherent manner.

see the docs here for introspection: 
https://docs.djangoproject.com/en/dev/howto/legacy-databases/?from=olddocs


 

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Re: using forloop.counter to access data

[Tom Evans]

On Wed, Mar 21, 2012 at 2:58 PM, Larry Martell  wrote:
> OK, but is there some reason {{ headers.0.forloop.counter } does not
> work when forloop.counter has a value of 2, yet {{ headers.0.2 }}
> does work?

Django never does variable interpolation when resolving dot separated variables.

What django does do when it resolves dot separated variables is well documented:

https://docs.djangoproject.com/en/1.3/topics/templates/#variables

So outputting 'headers.0.forloop.counter' first finds the 'headers'
variable, and gets the 0th entry. In fact, first of all it tries

  headers.get('0')

IE, a dictionary lookup. This fails, so it tries

  getattr(headers, '0')

IE, an attribute lookup. This fails, so it tries

  headers.0() *

IE, a method call. This fails, so it tries

  headers[0]

IE, a list index lookup.

Having got 'headers.0' resolved, it would then step on to the next
part of the lookup - 'forloop'.

I think if you trace through yourself what it will do to lookup
forloop as a dictionary entry of headers[0], an attribute of
headers[0], a method call of headers[0] or a list index lookup of
headers[0], you will see that obviously all of these would fail. If
you replace forloop.counter with the raw value '2' and repeat the
process, you'll see why that works as well.

Cheers

Tom

* It doesn't actually do this, I haven't checked the code, but it
probably does something like this:

  val = headers.get('0')
  if not val:
val = getattr(headers, '0')
if callable(val):
  return val()
  if not val:
val = headers[0]
  return val

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Re: using forloop.counter to access data

[Larry Martell]

On Wed, Mar 21, 2012 at 8:32 AM, Tom Evans  wrote:
> On Wed, Mar 21, 2012 at 12:47 PM, Larry Martell  
> wrote:
>> This is probably a stupid newbie question 
>>
>> I want to access a column of data in a row using forloop.counter, but
>> I cannot get it to work.
>>
>> In my test code, if I display {{ forloop.counter }} I get 2
>> If I display {{ headers.0.2 }} I get ToolType
>> But if I display {{ headers.0.forloop.counter }} I get nothing
>>
>> What is the proper syntax for this?
>>
>
> The preferred solution is to structure your data better in your view
> so that writing the template to render the data is straightforward.

This is a very large existing app, and I am new at this job. That have
a table of data and they want me to make some of the data in the table
into links that take them to a more detailed view of the data. The
functionality to provide this more detailed view of the data already
exist in the app. So I am just trying to construct the href. As I
iterate through the table data, I need info from the header to build
the href.

>
> The pragmatic solution is to use a custom filter to access your
> current data structures:
>
> http://stackoverflow.com/questions/2024660/django-sort-dict-in-template

OK, but is there some reason {{ headers.0.forloop.counter } does not
work when forloop.counter has a value of 2, yet {{ headers.0.2 }}
does work?

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Re: using forloop.counter to access data

[Larry Martell]

On Wed, Mar 21, 2012 at 7:53 AM, James  wrote:
>
>
> On Wednesday, March 21, 2012 8:47:23 AM UTC-4, larry@gmail.com wrote:
>>
>> This is probably a stupid newbie question 
>>
>> I want to access a column of data in a row using forloop.counter, but
>> I cannot get it to work.
>>
>> In my test code, if I display {{ forloop.counter }} I get 2
>> If I display {{ headers.0.2 }} I get ToolType
>> But if I display {{ headers.0.forloop.counter }} I get nothing
>>
>> What is the proper syntax for this?
>
>
> the forloop.counter and friends will simply give you information about the
> iteration, it won't give you any information about the data in the queryset

Yes, I realize that. I am using it withing a loop to try an access a
specific item of data. The code I showed was just an example from one
iteration of the loop.

> (I'm assuming this is what you mean when you say column).
>
> Here are the
> docs https://docs.djangoproject.com/en/dev/ref/templates/builtins/?from=olddocs#for
>
>  If you want to access the column of data, assuming it's referenced from a
> model, just the attribute of that model. If you passed in a list to the
> template, you just use the django "dot" look-up syntax.

Perhaps my question wasn't clear. I have a list called headers. From
within a for loop I want the n'th item from the first row. In the loop
I am trying to access {{ headers.0.forloop.counter }} but I get no
value from that. But if I hard code the number (as a test), e.g.:  {{
headers.0.2 }} then I do get the value.

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Re: using forloop.counter to access data

[Tom Evans]

On Wed, Mar 21, 2012 at 12:47 PM, Larry Martell  wrote:
> This is probably a stupid newbie question 
>
> I want to access a column of data in a row using forloop.counter, but
> I cannot get it to work.
>
> In my test code, if I display {{ forloop.counter }} I get 2
> If I display {{ headers.0.2 }} I get ToolType
> But if I display {{ headers.0.forloop.counter }} I get nothing
>
> What is the proper syntax for this?
>

The preferred solution is to structure your data better in your view
so that writing the template to render the data is straightforward.

The pragmatic solution is to use a custom filter to access your
current data structures:

http://stackoverflow.com/questions/2024660/django-sort-dict-in-template

Cheers

Tom

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Re: using forloop.counter to access data

[James]

On Wednesday, March 21, 2012 8:47:23 AM UTC-4, larry@gmail.com wrote:
>
> This is probably a stupid newbie question 
>
> I want to access a column of data in a row using forloop.counter, but
> I cannot get it to work.
>
> In my test code, if I display {{ forloop.counter }} I get 2
> If I display {{ headers.0.2 }} I get ToolType
> But if I display {{ headers.0.forloop.counter }} I get nothing
>
> What is the proper syntax for this?
>

the forloop.counter and friends will simply give you information about the 
iteration, it won't give you any information about the data in the queryset 
(I'm assuming this is what you mean when you say column).

Here are the docs 
https://docs.djangoproject.com/en/dev/ref/templates/builtins/?from=olddocs#for

 If you want to access the column of data, assuming it's referenced from a 
model, just the attribute of that model. If you passed in a list to the 
template, you just use the django "dot" look-up syntax.

Docs here: https://docs.djangoproject.com/en/dev/ref/templates/api/#render

So, let's say your list looks like a = [1,2,3,4] and in your context it 
looks like c ={'a':a}

if you want to reference the second "column" (index really) you would just 
do {{ a.1 }}, this will render the number "2".

You would use forloop.counter for something like, let's say we passed in 
hundreds of such lists. And, for whatever reason, once we reach the 100th 
iteration, we want the loop to end.

Then we would do this:

{% for list in list_of_lists %}
  {{ list.1 }}
{% if forloop.counter == 100 %}
{% endfor %}
{% endif %}
{% if forloop. last %} 
{% endfor %}
{% endif %} 

The last if / endif is not necessary, but I wanted to show some control 
flow using the forloop context. In fact, I wouldn't do this at all at the 
template level. I would instead limit the queryset to 100 when creating the 
queryset and pass that in and then just iterate over it like any other 
queryset, but I think you see what I mean.

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using forloop.counter to access data

[Larry Martell]

This is probably a stupid newbie question 

I want to access a column of data in a row using forloop.counter, but
I cannot get it to work.

In my test code, if I display {{ forloop.counter }} I get 2
If I display {{ headers.0.2 }} I get ToolType
But if I display {{ headers.0.forloop.counter }} I get nothing

What is the proper syntax for this?

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