Thank you Mike, it works !
Le samedi 24 février 2018 16:35:57 UTC+1, Mike Bayer a écrit :
>
> On Sat, Feb 24, 2018 at 5:33 AM, Sven <sven....@gmail.com <javascript:>>
> wrote:
> > Hello,
> >
> > I have now a small example which illustrates the problem.
> >
> > Program logic : each NPC inherites from Character and each NPC is based
> on a
> > prototype. It means, for example, that you can define the prototype
> > "red_guard" and then create 100 red guards all based on this prototype.
> Most
> > part of the NPC attributes are stored in the class Prototype. For
> example, I
> > can define in the prototype that a red guard has 1000 health point and
> it
> > will be reflected automatically in every NPC based on the prototype.
> This is
> > why, the __getattr_ function of NPC is looking in the prototype
> attributes.
>
>
> your NPC class is making it impossible to test if the class has an
> attribute present or not and additionally `__getattr__()` assumes that
> the "self.prototype" attribute is present, when it's not, causing an
> endless loop:
>
> class Character(object):
> def __init__(self):
> if hasattr(self, '_foo'):
> print("yup")
>
>
> class Prototype(object):
> pass
>
>
> class NPC(Character):
> def __init__(self):
> Character.__init__(self)
> self.prototype = Prototype()
>
> def __getattr__(self, nom_attr):
> return getattr(self.prototype, nom_attr)
>
> NPC()
>
>
> using pdb inside of __getattr__ would reveal that the attributes
> being asked for here start with underscores, so one way to work around
> this is:
>
> def __getattr__(self, nom_attr):
> if nom_attr.startswith("_"):
> return object.__getattribute__(self, nom_attr)
> else:
> return getattr(self.prototype, nom_attr)
>
>
>
>
>
>
>
>
> >
> > Code:
> >
> > from sqlalchemy import create_engine
> > from sqlalchemy.orm import sessionmaker
> > from sqlalchemy.ext.declarative import declarative_base
> > from sqlalchemy import Column, Integer, String, ForeignKey
> > from sqlalchemy import orm
> > from sqlalchemy.orm import relationship
> >
> > BaseBDD = declarative_base()
> > engine = create_engine('sqlite:///getattr_loop.db', echo=True)
> > Session = sessionmaker(bind=engine)
> > session = Session()
> >
> > class Prototype(BaseBDD):
> > __tablename__ = "prototypes"
> > id = Column(Integer, primary_key=True)
> >
> > npc = relationship("NPC", back_populates="prototype")
> >
> > class Character(BaseBDD):
> > __tablename__ = "personnages"
> > id = Column(Integer, primary_key=True)
> >
> > type = Column(String)
> >
> > __mapper_args__ = {
> > 'polymorphic_on':type,
> > 'polymorphic_identity':'personnage'
> > }
> >
> > class NPC(Character):
> >
> > prototype_id = Column(ForeignKey('prototypes.id'))
> > prototype = relationship("Prototype", back_populates="npc")
> >
> > __mapper_args__ = {
> > 'polymorphic_identity':'npc'
> > }
> >
> > def __init__(self, prototype):
> > Character.__init__(self)
> > self.prototype = prototype
> > prototype.npc.append(self)
> >
> > def __getattr__(self, nom_attr):
> > return getattr(self.prototype, nom_attr)
> >
> > BaseBDD.metadata.create_all(engine)
> >
> > proto_jean = Prototype()
> > jean = NPC(proto_jean)
> >
> > Trace:
> >
> > Traceback (most recent call last):
> > File "C:\Users\Sven\Downloads\loop_test_trace.py", line 52, in
> <module>
> > jean = NPC(proto_jean)
> > File "<string>", line 2, in __init__
> > File
> "C:\Python34\lib\site-packages\sqlalchemy\orm\instrumentation.py",
> > line 379, in _new_state_if_none
> > if hasattr(instance, self.STATE_ATTR):
> > File "C:\Users\Sven\Downloads\loop_test_trace.py", line 47, in
> __getattr__
> > return getattr(self.prototype, nom_attr)
> > File "C:\Python34\lib\site-packages\sqlalchemy\orm\attributes.py",
> line
> > 242, in __get__
> > return self.impl.get(instance_state(instance), dict_)
> > File "C:\Users\Sven\Downloads\loop_test_trace.py", line 47, in
> __getattr__
> > return getattr(self.prototype, nom_attr)
> > File "C:\Python34\lib\site-packages\sqlalchemy\orm\attributes.py",
> line
> > 242, in __get__
> > return self.impl.get(instance_state(instance), dict_)
> > File "C:\Users\Sven\Downloads\loop_test_trace.py", line 47, in
> __getattr__
> > return getattr(self.prototype, nom_attr)
> > File "C:\Python34\lib\site-packages\sqlalchemy\orm\attributes.py",
> line
> > 242, in __get__
> > return self.impl.get(instance_state(instance), dict_)
> > File "C:\Users\Sven\Downloads\loop_test_trace.py", line 47, in
> __getattr__
> > return getattr(self.prototype, nom_attr)
> >
> > Unfortunately, the line "return getattr(self.prototype, nom_attr)" is
> > causing an endless loop.
> >
> > Has someone a solution ? How can I avoid this loop ?
> >
> > Thank you !
> >
> > Sven
> >
> >
> > --
> > SQLAlchemy -
> > The Python SQL Toolkit and Object Relational Mapper
> >
> > http://www.sqlalchemy.org/
> >
> > To post example code, please provide an MCVE: Minimal, Complete, and
> > Verifiable Example. See http://stackoverflow.com/help/mcve for a full
> > description.
> > ---
> > You received this message because you are subscribed to the Google
> Groups
> > "sqlalchemy" group.
> > To unsubscribe from this group and stop receiving emails from it, send
> an
> > email to sqlalchemy+...@googlegroups.com <javascript:>.
> > To post to this group, send email to sqlal...@googlegroups.com
> <javascript:>.
> > Visit this group at https://groups.google.com/group/sqlalchemy.
> > For more options, visit https://groups.google.com/d/optout.
>
--
SQLAlchemy -
The Python SQL Toolkit and Object Relational Mapper
http://www.sqlalchemy.org/
To post example code, please provide an MCVE: Minimal, Complete, and Verifiable
Example. See http://stackoverflow.com/help/mcve for a full description.
---
You received this message because you are subscribed to the Google Groups
"sqlalchemy" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to sqlalchemy+unsubscr...@googlegroups.com.
To post to this group, send email to sqlalchemy@googlegroups.com.
Visit this group at https://groups.google.com/group/sqlalchemy.
For more options, visit https://groups.google.com/d/optout.
