On Sat, Feb 24, 2018 at 5:33 AM, Sven <sven.du...@gmail.com> 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+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. -- 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.