'NoneType' and 'float' Error - How to avoid NoneType

Question

I've tried to structure my code so if NoneType is a result it will be converted into 0. However, I still seem to get None past through to the next function. Why is that?

Error in line 321, in get_profit_loss_value_fees

result = self.get_profit_loss_value() - self.get_fees()

TypeError: unsupported operand type(s) for -: 'NoneType' and 'float'

def get_profit_loss_value(self):
    if self.get_exit_cpu() > 0:
        if self.type == 'Long':
            result = self.get_entries().aggregate(
            get_profit_loss_value=Sum('amount', output_field=models.FloatField()
                                           ) * (self.get_exit_cpu() - self.get_entry_cpu()))['get_profit_loss_value']
            return 0 if result is None else result
        elif self.type == 'Short':
            ...
    else:
        return 0

def get_profit_loss_value_fees(self):
    result = self.get_profit_loss_value() - self.get_fees()
    return result

---

As requested Entire Traceback:

Traceback (most recent call last):
  File "C:\Users\winkl\tj3\venv\lib\site-packages\django\core\handlers\exception.py", line 34, in inner
    response = get_response(request)
  File "C:\Users\winkl\tj3\venv\lib\site-packages\django\core\handlers\base.py", line 145, in _get_response
    response = self.process_exception_by_middleware(e, request)
  File "C:\Users\winkl\tj3\venv\lib\site-packages\django\core\handlers\base.py", line 143, in _get_response
    response = response.render()
  File "C:\Users\winkl\tj3\venv\lib\site-packages\django\template\response.py", line 105, in render
    self.content = self.rendered_content
  File "C:\Users\winkl\tj3\venv\lib\site-packages\django\template\response.py", line 83, in rendered_content
    return template.render(context, self._request)
  File "C:\Users\winkl\tj3\venv\lib\site-packages\django\template\backends\django.py", line 61, in render
    return self.template.render(context)
  File "C:\Users\winkl\tj3\venv\lib\site-packages\django\template\base.py", line 171, in render
    return self._render(context)
  File "C:\Users\winkl\tj3\venv\lib\site-packages\django\template\base.py", line 163, in _render
    return self.nodelist.render(context)
  File "C:\Users\winkl\tj3\venv\lib\site-packages\django\template\base.py", line 936, in render
    bit = node.render_annotated(context)
  File "C:\Users\winkl\tj3\venv\lib\site-packages\django\template\base.py", line 903, in render_annotated
    return self.render(context)
  File "C:\Users\winkl\tj3\venv\lib\site-packages\django\template\loader_tags.py", line 150, in render
    return compiled_parent._render(context)
  File "C:\Users\winkl\tj3\venv\lib\site-packages\django\template\base.py", line 163, in _render
    return self.nodelist.render(context)
  File "C:\Users\winkl\tj3\venv\lib\site-packages\django\template\base.py", line 936, in render
    bit = node.render_annotated(context)
  File "C:\Users\winkl\tj3\venv\lib\site-packages\django\template\base.py", line 903, in render_annotated
    return self.render(context)
  File "C:\Users\winkl\tj3\venv\lib\site-packages\django\template\loader_tags.py", line 62, in render
    result = block.nodelist.render(context)
  File "C:\Users\winkl\tj3\venv\lib\site-packages\django\template\base.py", line 936, in render
    bit = node.render_annotated(context)
  File "C:\Users\winkl\tj3\venv\lib\site-packages\django\template\base.py", line 903, in render_annotated
    return self.render(context)
  File "C:\Users\winkl\tj3\venv\lib\site-packages\django\template\defaulttags.py", line 209, in render
    nodelist.append(node.render_annotated(context))
  File "C:\Users\winkl\tj3\venv\lib\site-packages\django\template\base.py", line 903, in render_annotated
    return self.render(context)
  File "C:\Users\winkl\tj3\venv\lib\site-packages\django\template\defaulttags.py", line 309, in render
    return nodelist.render(context)
  File "C:\Users\winkl\tj3\venv\lib\site-packages\django\template\base.py", line 936, in render
    bit = node.render_annotated(context)
  File "C:\Users\winkl\tj3\venv\lib\site-packages\django\template\base.py", line 903, in render_annotated
    return self.render(context)
  File "C:\Users\winkl\tj3\venv\lib\site-packages\django\template\defaulttags.py", line 309, in render
    return nodelist.render(context)
  File "C:\Users\winkl\tj3\venv\lib\site-packages\django\template\base.py", line 936, in render
    bit = node.render_annotated(context)
  File "C:\Users\winkl\tj3\venv\lib\site-packages\django\template\base.py", line 903, in render_annotated
    return self.render(context)
  File "C:\Users\winkl\tj3\venv\lib\site-packages\django\template\base.py", line 986, in render
    output = self.filter_expression.resolve(context)
  File "C:\Users\winkl\tj3\venv\lib\site-packages\django\template\base.py", line 670, in resolve
    obj = self.var.resolve(context)
  File "C:\Users\winkl\tj3\venv\lib\site-packages\django\template\base.py", line 795, in resolve
    value = self._resolve_lookup(context)
  File "C:\Users\winkl\tj3\venv\lib\site-packages\django\template\base.py", line 857, in _resolve_lookup
    current = current()
  File "C:\Users\winkl\tj3\portfolios\models.py", line 321, in get_profit_loss_value_fees
    result = self.get_profit_loss_value() - self.get_fees()
TypeError: unsupported operand type(s) for -: 'NoneType' and 'float'

Answer 1

You could always make a wrapper around def get_profit_loss_value(self):

def get_profit_loss_value_or_None(self):
   # All code as now

def get_profit_loss_value(self):
    ret = self.get_profit_loss_value_or_None()
    return 0 if ret is None else ret

This may also protect against any future changes which result in unforeseen returns of None.