Stack Overflow MCVE - SqlAlchemy schema extension

from datetime import datetime, timedelta
import os

from sqlalchemy import Column, BigInteger, String, CHAR, TIMESTAMP
from sqlalchemy import create_engine, func
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.inspection import inspect
from sqlalchemy.orm.session import sessionmaker

# Part 1: Setup

OrmBase = declarative_base()

class Encounter(OrmBase):
    __tablename__ = 'encounter_table'
    encounterid = Column(BigInteger, primary_key=True)
    title = Column(String(64))
    starttime = Column(TIMESTAMP)
    endtime = Column(TIMESTAMP)


class Combatant(OrmBase):
    __tablename__ = 'combatant_table'
    combatantid = Column(BigInteger, primary_key=True)
    ally = Column(CHAR(1))
    name = Column(String(64))
    starttime = Column(TIMESTAMP)
    endtime = Column(TIMESTAMP)
    damage = Column(BigInteger)

envFile = 'envfile.txt'
if envFile != '' and envFile is not None:
    with open(envFile) as envVars:
        for line in envVars:
            var, val = line.split('=', 1)
            var = var.strip()
            val = val.strip()
            os.environ[var] = val

engine = create_engine(os.environ['DBCONNECTION'])
Session = sessionmaker(bind=engine)
dbSession = Session()

# Part 2: Where Things Work

columns = [
      {'attr': 'title', 'name': 'Encounter'},
      {'attr': 'starttime', 'name': 'Start Time'}
  ]

objects = dbSession.query(Encounter) \
        .filter(Encounter.endtime > (datetime.now() - timedelta(days=33))) \
        .order_by(Encounter.endtime.desc()).limit(5).all()

for obj in objects:
    for col in columns:
        v = inspect(obj).attrs[col['attr']].value
        printVal = col['formatter'](v) if col.get('formatter', None) else v
        print('Column:', col['name'], ', Value:', printVal)
    print('-----------')

# Part 3: Trying to extend the data model

def characterQuery(dbSession):
    return dbSession.query(
        Combatant.name.label('name'),
        func.min(Combatant.starttime).label('firstSeen'),
        func.max(Combatant.endtime).label('lastSeen'),
        func.sum(Combatant.damage).label('damage'),
                           ).group_by(Combatant.name)

# Part 4: Where things fall apart

columns = [
      {'attr': 'name', 'name': 'Character Name'},
      {'attr': 'firstSeen', 'name': 'First Seen'},
      {'attr': 'lastSeen', 'name': 'Last Seen'},
      {'attr': 'duration', 'name': 'Total Seen (s)'},
      {'attr': 'damage', 'name': 'Total Damage'},
  ]

objects = characterQuery(dbSession) \
        .having(func.max(Combatant.endtime) >
                (datetime.now() - timedelta(days=33))) \
        .order_by(func.max(Combatant.endtime).desc()).limit(25).all()

for obj in objects:
    for col in columns:
        v = inspect(obj).attrs[col['attr']].value
        printVal = col['formatter'](v) if col.get('formatter', None) else v
        print('Column:', col['name'], ', Value:', printVal)
    print('-----------')