CODEWITHSUNDEEP
pythondjango
jayt
jayt

Reputation: 768

Django - Unsupported operand type(s) for decimal and method

I'm trying to add two values (one from a method and one from a field) in my Django models.py.

class Object(models.Model):
    value = models.DecimalField()
    def scaled_value(self):
        scaled_val = float(self.value) * 3
        return scaled_val
    def add_val_and_scaled_val(self):
        sum = self.scaled_value + self.value
        return sum

When I try to get the value of the sum from the 'add_val_and_scaled_val' method in my template like this {% Object.add_val_and_scaled_val %} then I get the TypeError...

TypeError at /objects/detail/object-12345678/
unsupported operand type(s) for +: 'instancemethod' and 'Decimal'

The instancemethod which the error refers to (self.scaled_value) should return a decimal value should it not? What am I doing wrong? Thanks.

Upvotes: 0

Views: 963

Answers (2)

Daniel Roseman
Daniel Roseman

Reputation: 599490

scaled_value is a method, you need to call it in your calculation not just refer to it.

sum = self.scaled_value() + self.value

(Although I'm not sure of the point of any of this code. x*3 + x just equals x*4, no?)

Upvotes: 1

jamylak
jamylak

Reputation: 133514

The instancemethod which the error refers to (self.scaled_value) should return a decimal value should it not

def scaled_value(self):
    scaled_val = float(self.value) * 3
    return scaled_val

No it shouldn't because in scaled_value you explicity convert to a float

Also you need to change this code 

def add_val_and_scaled_val(self):
    sum = self.scaled_value() + self.value # you had self.scaled_value
    return sum

You should reconsider adding float and Decimal however

Lastly, would recommend against shadowing the builtin sum function with sum = ...

Upvotes: 0

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