High numerical precision floats with MySQL and the SQLAlchemy ORM

Question

I store some numbers in a MySQL using the ORM of SQLAlchemy. When I fetch them afterward, they are truncated such that only 6 significant digits are conserved, thus losing a lot of precision on my float numbers. I suppose there is an easy way to fix this but I can't find how. For example, the following code:

import sqlalchemy as sa
from sqlalchemy.pool import QueuePool
import sqlalchemy.ext.declarative as sad

Base    = sad.declarative_base()
Session = sa.orm.scoped_session(sa.orm.sessionmaker())

class Test(Base): 
    __tablename__   = "test"
    __table_args__  = {'mysql_engine':'InnoDB'}
    no      = sa.Column(sa.Integer, primary_key=True)
    x       = sa.Column(sa.Float)


a = 43210.123456789
b = 43210.0
print a, b, a - b

dbEngine = sa.create_engine("mysql://chore:BlockWork33!@localhost", poolclass=QueuePool, pool_size=20,  
                                 pool_timeout=180)              
Session.configure(bind=dbEngine)   
session = Session()            

dbEngine.execute("CREATE DATABASE IF NOT EXISTS test")
dbEngine.execute("USE test")  
Base.metadata.create_all(dbEngine)   

try:
    session.add_all([Test(x=a), Test(x=b)])
    session.commit()
except:
    session.rollback()
    raise

[(a,), (b,)] = session.query(Test.x).all()
print a, b, a - b

produces

43210.1234568 43210.0 0.123456788999
43210.1 43210.0 0.0999999999985

and I would need a solution for it to produce

43210.1234568 43210.0 0.123456788999
43210.1234568 43210.0 0.123456788999

Answer 1

Per our discussion in the comments: sa.types.Float(precision=[precision here]) instead of sa.Float allows you to specify precision; however, sa.Float(Precision=32) has no effect. See the documentation for more information.