Re: missing required positional arguments

On Thu, Nov 17, 2016 at 03:28:24AM +0000, Boylan, Ross wrote:
> I'm having trouble pulling an instance back from the database (ZEO).  It's a revision object from hglib package.  My first try did not import hglib in the client; the second try did.  Both got the same error; see below for fuller output.
> 
> Maybe the type in the database is defined using some kind of nested class I can't easily access, maybe tng.hglib.revision?
> 
> https://selenic.com/repo/python-hglib/file/tip/hglib/client.py defines
> class revision(tuple):
>     def __new__(cls, rev, node, tags, branch, author, desc, date):
>         return tuple.__new__(cls, (rev, node, tags, branch, author, desc, date))

This class does not support pickling.  Try it:

   >>> import pickle
   >>> r = revision(1, 2, 3, 4, 5, 6, 7)
   >>> p = pickle.dumps(r)
   >>> r2 = pickle.loads(p)

The simplest way to make it pickle-compatible would be to override
revision.__getnewargs__().

> Fuller history:
> Most of my code is in a package/module tng
> In an interactive session I did
> from tng import *
> as well as importing ZEO and other stuff, but NOT hglib.
> In the session I retrieved an object from the database, called a method on it that causes the 
> revision to be set (inside my module is an import hglib), and committed.
> 
> In another session I tried to read the object I just wrote.  That session did from tng import *; as noted I tried with and without import hglib.  Here's the error from that session:
> 
> Couldn't load state for tng.Basics.BigBatch 0x044d
> Traceback (most recent call last):
>   File "/home/ross/.local/lib/python3.4/site-packages/ZODB-5.0.0-py3.4.egg/ZODB/Connection.py", line 757, in setstate
>     self._reader.setGhostState(obj, p)
>   File "/home/ross/.local/lib/python3.4/site-packages/ZODB-5.0.0-py3.4.egg/ZODB/serialize.py", line 622, in setGhostState
>     state = self.getState(pickle)
>   File "/home/ross/.local/lib/python3.4/site-packages/ZODB-5.0.0-py3.4.egg/ZODB/serialize.py", line 615, in getState
>     return unpickler.load()
> TypeError: __new__() missing 6 required positional arguments: 'node', 'tags', 'branch', 'author', 'desc', and 'date'
> [the entire error was printed twice for some reason]

This is because the inherited tuple.__getnewargs__ returns a tuple with
one argument (which is a tuple itself) that is then passed to __new__.

HTH,
Marius Gedminas
-- 
There are 10 kinds of people in the world: Those who understand binary
mathematics and those who don't.

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