Proper way to declare custom exceptions in modern Python?

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Proper way to declare custom exceptions in modern Python?

original source : https://stackoverflow.com/questions/1319615/proper-way-to-declare-custom-exceptions-in-modern-python

#1 answer for me 

With modern Python Exceptions, you don’t need to abuse .message, or override .__str__() or .__repr__() or any of it. If all you want is an informative message when your exception is raised, do this:

class MyException(Exception):
    pass

raise MyException("My hovercraft is full of eels")

That will give a traceback ending with MyException: My hovercraft is full of eels.

If you want more flexibiilty from the exception, you could pass a dictionary as the argument:

raise MyException({"message":"My hovercraft is full of animals", "animal":"eels"})

However, to get at those details in an except block is a bit more complicated; they are stored in the args attribute, which is a list. You would need to do something like this:

try:
    raise MyException({"message":"My hovercraft is full of animals", "animal":"eels"})
except MyException as e:
    details = e.args[0]
    print(details["animal"])

It is still possible to pass in multiple items into the exception, but this will be deprecated in the future. If you do need more than a single piece of information, then you should consider fully subclassing Exception.

#2 answer for me 

Maybe I missed the question, but why not:

class MyException(Exception):
    pass

Edit: to override something (or pass extra args), do this:

class ValidationError(Exception):
    def __init__(self, message, errors):

        # Call the base class constructor with the parameters it needs
        super(ValidationError, self).__init__(message)

        # Now for your custom code...
        self.errors = errors

That way you could pass dict of error messages to the second param, and get to it later with e.errors

Django many to many relationship with join table-specific fields

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Django many to many relationship with join table-specific fields

original source : https://stackoverflow.com/questions/21366680/django-many-to-many-relationship-with-join-table-specific-fields

Using the through argument to ManyToManyField you can explicitly define the join table and put the balance field there.

class Orgs(models.Model):
    ...
    members = ManyToManyField(Members, through='Membership')

class Members(models.Model):
    ...

class Membership(models.Model)
    org = models.ForeignKey(Orgs)
    member = models.ForeignKey(Members)
    balance = models.DecimalField()  # or whatever your field type is