'NoneType' 和 'float' 错误 - 如何避免 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

There's probably a possibility for self.type that you are either not checking or checking but then not returning anything. If you don't return anything, python will return None for you.

So if for example self.get_exit_cpu() is bigger than 0, but self.type is something you're not checking, say "Long Long" , then the else statement won't execute and nothing will be manually returned - meaning None will be returned.

Answer 2

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 .