python - How to subtract two fields in django templates? -

before marking duplicate numerous other questions on so, read. have 3 fields, credit available, credit limit , credit balance. i'm getting values credit limit , credit balance database. display credit available, want credit limit-credit balance. tried doing other answers on stackoverflow, did not work

<tr>     <td style="text-align:center">{{ credit.credit_limit|add:"-{{credit.credit_balance}}" }}</td>     <td align="center">{{ credit.credit_limit}}</td>     <td align="center">{{ credit.credit_balance }}</td> </tr> 

can without writing new template tags or using mathfilter module?

the correct syntax adding limit balance is

{{ credit.credit_limit|add:credit.credit_balance }} 

as per https://docs.djangoproject.com/en/1.10/ref/templates/builtins/#add. unfortunately, putting minus sign in front of variable won't work make negative.

you use custom template filter, straightforward. might this:

@register.filter(name='subtract') def subtract(value, arg):     return value - arg 

then in template (after loading it) be:

{{ credit.credit_limit|subtract:credit.credit_balance }}