如何在 django 中执行数学运算？

Question

i am trying to calculate the new_balance when a user withdraw any amount from thier main balance .

i am trying to perform this operation when the form is being submitted but i do not know if this is the perfect way to perform this operations. This is what i am trying to achive.

def withdrawal_request(request):
    ...
    if request.method == "POST":
        form = WithWithdrawalRequestForm(request.POST)
        if form.is_valid():
            new_form = form.save(commit=False)
            new_form.user = request.user

            if new_form.amount > all_earning:
                messages.warning(request, "You cannot withdraw more than what is in your wallet balance.")
                return redirect("core:withdrawal-request")
            elif pending_payout > new_balance:
                messages.warning(request, "You have reached your wallet limit")
                return redirect("core:withdrawal-request")
            else:
                new_form.save()
                new_balance = new_balance - new_form.amount
                messages.success(request, f"Withdrawal Request Is Been Processed...")
                return redirect("core:withdrawal-request")
        
    else:
        form = WithWithdrawalRequestForm(request.POST)
        

    context = {
            "form":form,
            "new_balance":new_balance,
        }
    return render(request, "core/withdrawal-request.html", context)

Answer 1

I was actually missing one more line

else:
   new_form.save()
   request.user.profile.main_all_earning = main_all_earning - new_form.amount
   request.user.profile.save()
   messages.success(request, f"Withdrawal Request Is Been Processed...")
   return redirect("core:withdrawal-request")

Answer 2

        else:
            new_form.save()
            new_balance = new_balance - new_form.amount
            messages.success(request, f"Withdrawal Request Is Been Processed...")
            return redirect("core:withdrawal-request")
    
else:
    form = WithWithdrawalRequestForm(request.POST)
    

context = {
        "form":form,
        "new_balance":new_balance,
    }
return render(request, "core/withdrawal-request.html", context)

You're returning at the end of the upper else statement, so you can't reach the line where you update your context . In Python a function exits after returning.