问为什么使用sqlite插入SQLAlchemy比直接使用sqlite3慢25倍？

EN

#!/usr/bin/env python
# Why is SQLAlchemy with SQLite so slow?
# Output from this program:
# SqlAlchemy: Total time for 100000 records 10.74 secs
# sqlite3:    Total time for 100000 records  0.40 secs


import time
import sqlite3

from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, Integer, String,  create_engine 
from sqlalchemy.orm import scoped_session, sessionmaker

Base = declarative_base()
DBSession = scoped_session(sessionmaker())

class Customer(Base):
    __tablename__ = "customer"
    id = Column(Integer, primary_key=True)
    name = Column(String(255))

def init_sqlalchemy(dbname = 'sqlite:///sqlalchemy.db'):
    engine  = create_engine(dbname, echo=False)
    DBSession.configure(bind=engine, autoflush=False, expire_on_commit=False)
    Base.metadata.drop_all(engine)
    Base.metadata.create_all(engine)

def test_sqlalchemy(n=100000):
    init_sqlalchemy()
    t0 = time.time()
    for i in range(n):
        customer = Customer()
        customer.name = 'NAME ' + str(i)
        DBSession.add(customer)
    DBSession.commit()
    print "SqlAlchemy: Total time for " + str(n) + " records " + str(time.time() - t0) + " secs"

def init_sqlite3(dbname):
    conn = sqlite3.connect(dbname)
    c = conn.cursor()
    c.execute("DROP TABLE IF EXISTS customer")
    c.execute("CREATE TABLE customer (id INTEGER NOT NULL, name VARCHAR(255), PRIMARY KEY(id))")
    conn.commit()
    return conn

def test_sqlite3(n=100000, dbname = 'sqlite3.db'):
    conn = init_sqlite3(dbname)
    c = conn.cursor()
    t0 = time.time()
    for i in range(n):
        row = ('NAME ' + str(i),)
        c.execute("INSERT INTO customer (name) VALUES (?)", row)
    conn.commit()
    print "sqlite3: Total time for " + str(n) + " records " + str(time.time() - t0) + " sec"

if __name__ == '__main__':
    test_sqlalchemy(100000)
    test_sqlite3(100000)