Python数据结构-我需要使用SQL插件吗？如果需要，如何使用？

Question

I have the following class with associated attributes:

class Company(object):
    self.ticker # string
    self.company # string
    self.creator # string
    self.link # string
    self.prices # list of tuples (this could be many hundreds of entries long)
    self.creation_date # date entry

I populate individual companies and then store a list of companies into class Companies:

class Companies(object):
    def __init__(self):
        self.companies = []
    def __len__(self):
        return len(self.companies)
    def __getitem__(self, key):
        return self.companies[key]
    def __repr__(self):
        return 'Company list of length %i' % (self.__len__())
    def add(self, company):
        self.companies.append(company)

I want to be able to easily perform queries such as Companies.find(creator="someguy") and have the class return a list of all companies created by someguy. I also want to be able to run a query such as Companies.find(creation_date > x) and return a list of all entries created after a certain date.

I have a little bit of experience of doing similar work with Django's built in SQL functionality and found that to be pretty convenient. However, this project isn't using Django and I don't know if there are any other, smaller packages that provide this functionality. I'd like to keep the interfacing with the SQL server to a minimum because I don't have much experience with the language.

Here are my questions:

1. To do the above, do I need to use an external database program? Or, does a package exist that will do the above, and also allow me to easily save the data (pickling or other)? I feel, perhaps unjustifiably so, that things start becoming messier and more complicated when you start incorporating SQL.
2. If a database is not necessary for the above, how do you evaluate when you have enough data where you will want to incorporate an external database?
3. What packages, eg Django, exist to minimize the SQL legwork?
4. All this being said, what do you recommend I do?

Answer 1

SQLAlchemy is a full featured Python ORM (Object Relational Mapper). It can be found at http://www.sqlalchemy.org/ .

Example usage to define a new object:

from sqlalchemy import Column, Integer, String

class User(Base):
    __tablename__ = 'users'

    id = Column(Integer, primary_key=True)
    name = Column(String)
    fullname = Column(String)
    password = Column(String)

def __init__(self, name, fullname, password):
    self.name = name
    self.fullname = fullname
    self.password = password

To create a new User:

>>> ed_user = User('ed', 'Ed Jones', 'edspassword')
>>> ed_user.name
'ed'
>>> ed_user.password
'edspassword'

To write to the database (after creating a new session):

ed_user = User('ed', 'Ed Jones', 'edspassword')
session.add(ed_user)
session.commit()

And to query:

our_user = session.query(User).filter_by(name='ed').first() 
>>> our_user
<User('ed','Ed Jones', 'edspassword')>

More details can be found at http://docs.sqlalchemy.org/en/rel_0_8/orm/tutorial.html (taken from docs).