Question

I am using YAML and SQLAlchemy. I defined my object, and I am able to use YAML to print that just fine. However, when I try to use YAML on the object returned from a SQLAlchemy query, it is failing with the error can't pickle int objects. I printed out the instance returned from SQLAlchemy, and it is showing the correct type. I’ll let the code do the talking:

class HashPointer(Base):
    __tablename__ = 'hash_pointers'

    id = Column(Integer, primary_key=True)
    hash_code = Column(VARBINARY(64), unique=True)
    file_pointer = Column(Text)

    def __init__(self, hash_code, file_pointer):
        self.hash_code = hash_code
        self.file_pointer = file_pointer

    def __repr__(self):
        return "<HashPointer('%s', '%s')>" % (self.hash_code, self.file_pointer)

from sqlalchemy import create_engine
from sqlalchemy.orm import sessionmaker
Engine = create_engine("mysql://user:pass@localhost/db", echo=True)
Session = sessionmaker(bind=Engine)
session = Session()
fhash = HashPointer(0x661623708235, "c:\\test\\001.txt")

# PRINTS FINE
print(yaml.dump(fhash))

for instance in session.query(HashPointer).all():
    # PRINTS FINE AS __repr__
    print instance

    # THROWS ERROR, 'CAN'T PICKLE INT OBJECTS'
    print(yaml.dump(instance))

Answer 1

Try adding the following to your class:

def __reduce__(self):
    'Return state information for pickling'
    return self.__class__, (int(self.hash_code), str(self.file_pointer))