Math filter

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sum abiut

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Jul 18, 2017, 10:22:09 PM7/18/17
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Hi,
needed direction maths filters on django templates. for example how to you perform this on a template.

a*b +b*c

i did      a|mul:b|add:b|mul:c    but got a wrong answer. Please point me to right direction.

cheers,

James Schneider

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Jul 19, 2017, 1:51:21 AM7/19/17
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I wouldn't do any sort of advanced math in the template. It should be completed in the view and added to the template context, then referenced as a template variable. The template processor has no concept of the order of operations in math. 

-James 

Vijay Khemlani

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Jul 19, 2017, 8:42:51 AM7/19/17
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Also I guess mathfilters just executes left-to-right

so

a|mul:b|add:b|mul:c

is (((a * b) + b) * c)

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Mike Morris

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Jul 19, 2017, 6:41:04 PM7/19/17
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I am a newbie, but I think the answer is that you can't do that in the template - instead, calculate the number in the view and pass it to the template in the context dictionary.

I think it's a design philosophy of Django Template Language to not support this as it muddies the border between data and presentation. They've obviously made some exceptions for the really common/easy use cases - like "|add"

There are other template languages that do support that of course; if its important enough you could look at changing the template engine...

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Mike Morris

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Jul 19, 2017, 7:29:00 PM7/19/17
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Of course, if they're integers you could implement the "mul" as a loop of "add"s... clumsy, but would work.

Vijay Khemlani

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Jul 19, 2017, 9:21:08 PM7/19/17
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I'm guessing he's using the mathfilters package


On Wed, Jul 19, 2017 at 7:28 PM, Mike Morris <mi...@musicplace.com> wrote:

Of course, if they're integers you could implement the "mul" as a loop of "add"s... clumsy, but would work.


On 07/19/2017 03:39 PM, Mike Morris wrote:

I am a newbie, but I think the answer is that you can't do that in the template - instead, calculate the number in the view and pass it to the template in the context dictionary.

I think it's a design philosophy of Django Template Language to not support this as it muddies the border between data and presentation. They've obviously made some exceptions for the really common/easy use cases - like "|add"

There are other template languages that do support that of course; if its important enough you could look at changing the template engine...




On 07/18/2017 07:21 PM, sum abiut wrote:
Hi,
needed direction maths filters on django templates. for example how to you perform this on a template.

a*b +b*c

i did      a|mul:b|add:b|mul:c    but got a wrong answer. Please point me to right direction.

cheers,
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Mike Morris

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Jul 19, 2017, 10:03:40 PM7/19/17
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On 07/19/2017 06:20 PM, Vijay Khemlani wrote:
> I'm guessing he's using the mathfilters package
>
> https://github.com/dbrgn/django-mathfilters

Arggghhh... my ignorance is showing! I hope I included an "I'm new here" disclaimer in the original post!!!

Anyway, never heard of it, I'll take a look!

Thank You Vijay!


Vijay Khemlani

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Jul 20, 2017, 8:46:34 AM7/20/17
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Don't worry, I only knew about the project because I use it in a small part of an application that can't execute computations on the view

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