[Twisted-Python] Inheriting DatagramProtocol, which is an old-style class

Tom Most twm at freecog.net
Fri Feb 7 22:58:48 MST 2020


Old-style classes remain old-style for compatibility reasons. You have some options, though:

1. Set the TWISTED_NEWSTYLE environment variable [1] to make all such old-style classes new-style.
2. When subclassing it, also subclass object, making the result new-style.
3. Switch to Python 3, where all-classes are new-style.

Option 3 is the best, since we will drop Python 2.7 support soon enough. Option 1 may be helpful when migrating a codebase.

---Tom

[1]: https://github.com/twisted/twisted/blob/c0a51509974e995537212efc5074140388585da6/src/twisted/python/compat.py#L61

On Fri, Feb 7, 2020, at 9:44 PM, Maarten ter Huurne wrote:
> On Saturday, 8 February 2020 01:50:04 CET Go Luhng wrote:
> > I am creating a child class
> > `Child(twisted.internet.protocol.DatagramProtocol)` to implement a
> > custom UDP multicast protocol.
> > 
> > I need to add an `__init__()` to `Child`, but as part of that I need
> > to call `super()` which is impossible because `DatagramProtocol` is
> > old-style.
> > 
> > How should I proceed?
> 
> There is no __init__() in DatagramProtocol or in its superclass 
> AbstractDatagramProtocol, so you can just skip the call.
> 
> > Also, why are there old-style classes in the latest release of
> > Twisted?
> 
> I don't know the reason, but it seems to be deliberate, since 
> AbstractDatagramProtocol is annotated with @_oldStyle in the source.
> 
> Bye,
> 		Maarten



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