TypeError: unsupported operand type(s) for /: 'float' and 'decimal.Decimal'

Question

Let us consider my views.py

def ajax_add_other_order_item(request,id):
   client = request.user.client

   def _convert(from_currency, to_currency, price):
       custom_rate_obj = client.custom_rates.filter(currency=to_currency).first()
       if custom_rate_obj is None or custom_rate_obj.exchange_rate in (0, None):
          custom_rate_obj = ExchangeRates.objects.latest('created')
       return custom_rate_obj.convert(from_currency, to_currency, price)
   if request.method == 'POST':
      unit = request.POST.get('u_price') or 0
      if supplier.currency:
         currency = supplier.currency
      else:
         currency = request.POST.get('currency', 'GBP')
      purchase_price = _convert(currency, 'GBP', float(unit))
      try:
          exchange_price = float(unit)/purchase_price
      except ZeroDivisionError:
          exchange_price = 0
      if form_brought_in == 'CT':
            val = 2.5
      elif form_brought_in == 'BR' or form_brought_in == 'RB':
            val = 3.5
      else:
            val = 0.0
     trade_price = math.ceil(_convert(currency, client.currency, float(unit)) * val)

here is my models.py (where custom_rate_obj.convert function is defined)

class ExchangeRates(TimeStampedModel):
    date = models.DateField(unique=True)
    timestamp = models.BigIntegerField(blank=True, null=True)
    base_currency = models.CharField(max_length=10, default='GBP')
    data = JSONField()

    def get_currency_rate(self, currency):
        return Decimal(self.data[currency])

    def convert(self, from_currency, to_currency, value):
        from_rate = self.get_currency_rate(from_currency)
        to_rate = self.get_currency_rate(to_currency)


        return round((Decimal(value or 0) / from_rate) * to_rate, 6)

Here is my error traceback

Traceback (most recent call last):
  File "/home/harika/lightdegree/lib/python3.7/site-packages/django/core/handlers/exception.py", line 34, in inner
    response = get_response(request)
  File "/home/harika/lightdegree/lib/python3.7/site-packages/django/core/handlers/base.py", line 115, in _get_response
    response = self.process_exception_by_middleware(e, request)
  File "/home/harika/lightdegree/lib/python3.7/site-packages/django/core/handlers/base.py", line 113, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "/home/harika/lightdegree/lib/python3.7/site-packages/django/views/decorators/csrf.py", line 54, in wrapped_view
    return view_func(*args, **kwargs)
  File "/home/harika/lightdegree/lib/python3.7/site-packages/django/contrib/auth/decorators.py", line 21, in _wrapped_view
    return view_func(request, *args, **kwargs)
  File "/home/harika/krishna test/dev-1.8/mcam/server/mcam/stock/views.py", line 4476, in ajax_add_other_order_item
    trade_price = math.ceil(_convert(currency, client.currency, float(unit)) * val)
TypeError: unsupported operand type(s) for *: 'decimal.Decimal' and 'float'

Here i am getting error TypeError: unsupported operand type(s) for /: 'float' and 'decimal.Decimal' Please help to solve this issue

Answer 1

You can not divide a float with a Decimal, since a decimal has a fixed number of digits, whereas a float uses the IEEE-754 encoding and has not a fixed number of digits.

You can convert the number to a Decimal, and then do the division accordingly:

from decimal import Decimal

try:
    exchange_price = Decimal(unit)/purchase_price
except ZeroDivisionError:
    exchange_price = Decimal(0)

for the vals you should do the same:

if form_brought_in == 'CT':
    val = Decimal('2.5')
elif form_brought_in == 'BR' or form_brought_in == 'RB':
    val = Decimal('3.5')
else:
    val = Decimal(0)

Answer 2

from decimal import Decimal

...

exchange_price = Decimal(unit)/purchase_price