with_entities2.py

# -*- coding:utf-8 -*-
import sqlalchemy as sa
from sqlalchemy.sql import func as f
import sqlalchemy.orm as orm
from sqlalchemy.ext.declarative import declarative_base

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

class Person(Base):
    __tablename__ = "Person"
    query = Session.query_property()
    id = sa.Column(sa.Integer, primary_key=True)
    blood = sa.Column(sa.String(1)) #sloppy
    gender = sa.Column(sa.String(1)) #sloppy


"""
Person
id,  gender, blood
1,   F       A   
2,   M       AB  
3,   M       B   
4,   F       O   
5,   M       O   
"""

engine = sa.create_engine("sqlite://")
Session.bind = engine
Base.metadata.bind = engine
Base.metadata.create_all()

Session.add(Person(gender="F", blood="A"))
Session.add(Person(gender="M", blood="AB"))
Session.add(Person(gender="M", blood="B"))
Session.add(Person(gender="F", blood="O"))
Session.add(Person(gender="M", blood="O"))

q = Person.query
## q = some_filter(q)

q = q.with_entities(
    Person.blood, 
    f.sum(sa.case([(Person.gender=="F", 1)], else_=0)).label("F"), 
    f.sum(sa.case([(Person.gender=="M", 1)], else_=0)).label("M"), 
)
print("Blod, F, M")
for row in q.group_by(Person.blood).all():
    print("{o.blood}, {o.F}, {o.M}".format(o=row))

"""
Blod, F, M
A, 1, 0
AB, 0, 1
B, 0, 1
O, 1, 1
"""