Python 每次重新启动程序时删除Sqlite3数据库

更新： 我删除了drop表if exists行，并得到了错误

python minitwit.py
Traceback (most recent call last):
  File "minitwit.py", line 254, in <module>
    init_db()
  File "minitwit.py", line 57, in init_db
    db.cursor().executescript(f.read())
sqlite3.OperationalError: table user already exists

我正在运行这个名为minitwit的免费烧瓶示例，希望对其稍加修改。每次重新启动程序时，我都无法使用以前注册的用户登录。我使用终端中的命令行检查了数据库，看它是否真的不在那里，表是空的！如何使数据库中的数据在每次重新启动程序时保持不变？谢谢

Flask的演示程序minitwit：

---

我刚刚向这个init_db方法添加了try-except块，还从schema.sql中删除了drop-table if-exists行。请参阅问题中的update，现在我可以重新启动程序并从数据库加载保存的数据

def init_db():
    """Creates the database tables."""
    with app.app_context():
        db = get_db()
        with app.open_resource('schema.sql', mode='r') as f:
            try:
                db.cursor().executescript(f.read())
            except sqlite3.OperationalError, msg:
                print msg
        db.commit()

---

问题可能是schema.sql中的内容。@ScottHunter我添加了schema.sql。一个想法：为了避免这种情况，我认为应该在应用程序启动时这样做：1检查数据库文件是否已经存在1a如果已经存在，打开并继续进行2如果没有，调用init_db来创建表。这样，代码只在必要时被调用。

# -*- coding: utf-8 -*-
"""
    MiniTwit
    ~~~~~~~~

    A microblogging application written with Flask and sqlite3.

    :copyright: (c) 2010 by Armin Ronacher.
    :license: BSD, see LICENSE for more details.
"""

import time
from sqlite3 import dbapi2 as sqlite3
from hashlib import md5
from datetime import datetime
from flask import Flask, request, session, url_for, redirect, \
     render_template, abort, g, flash, _app_ctx_stack
from werkzeug import check_password_hash, generate_password_hash


# configuration
DATABASE = 'minitwit.db'
PER_PAGE = 30
DEBUG = True
SECRET_KEY = 'development key'

# create our little application :)
app = Flask(__name__)
app.config.from_object(__name__)
app.config.from_envvar('MINITWIT_SETTINGS', silent=True)


def get_db():
    """Opens a new database connection if there is none yet for the
    current application context.
    """
    top = _app_ctx_stack.top
    if not hasattr(top, 'sqlite_db'):
        top.sqlite_db = sqlite3.connect(app.config['DATABASE'])
        top.sqlite_db.row_factory = sqlite3.Row
    return top.sqlite_db


@app.teardown_appcontext
def close_database(exception):
    """Closes the database again at the end of the request."""
    top = _app_ctx_stack.top
    if hasattr(top, 'sqlite_db'):
        top.sqlite_db.close()


def init_db():
    """Creates the database tables."""
    with app.app_context():
        db = get_db()
        with app.open_resource('schema.sql', mode='r') as f:
            db.cursor().executescript(f.read())
        db.commit()


def query_db(query, args=(), one=False):
    """Queries the database and returns a list of dictionaries."""
    cur = get_db().execute(query, args)
    rv = cur.fetchall()
    return (rv[0] if rv else None) if one else rv


def get_user_id(username):
    """Convenience method to look up the id for a username."""
    rv = query_db('select user_id from user where username = ?',
                  [username], one=True)
    return rv[0] if rv else None


def format_datetime(timestamp):
    """Format a timestamp for display."""
    return datetime.utcfromtimestamp(timestamp).strftime('%Y-%m-%d @ %H:%M')


def gravatar_url(email, size=80):
    """Return the gravatar image for the given email address."""
    return 'http://www.gravatar.com/avatar/%s?d=identicon&s=%d' % \
        (md5(email.strip().lower().encode('utf-8')).hexdigest(), size)


@app.before_request
def before_request():
    g.user = None
    if 'user_id' in session:
        g.user = query_db('select * from user where user_id = ?',
                          [session['user_id']], one=True)


@app.route('/')
def timeline():
    """Shows a users timeline or if no user is logged in it will
    redirect to the public timeline.  This timeline shows the user's
    messages as well as all the messages of followed users.
    """
    if not g.user:
        return redirect(url_for('public_timeline'))
    return render_template('timeline.html', messages=query_db('''
        select message.*, user.* from message, user
        where message.author_id = user.user_id and (
            user.user_id = ? or
            user.user_id in (select whom_id from follower
                                    where who_id = ?))
        order by message.pub_date desc limit ?''',
        [session['user_id'], session['user_id'], PER_PAGE]))


@app.route('/public')
def public_timeline():
    """Displays the latest messages of all users."""
    return render_template('timeline.html', messages=query_db('''
        select message.*, user.* from message, user
        where message.author_id = user.user_id
        order by message.pub_date desc limit ?''', [PER_PAGE]))


@app.route('/<username>')
def user_timeline(username):
    """Display's a users tweets."""
    profile_user = query_db('select * from user where username = ?',
                            [username], one=True)
    if profile_user is None:
        abort(404)
    followed = False
    if g.user:
        followed = query_db('''select 1 from follower where
            follower.who_id = ? and follower.whom_id = ?''',
            [session['user_id'], profile_user['user_id']],
            one=True) is not None
    return render_template('timeline.html', messages=query_db('''
            select message.*, user.* from message, user where
            user.user_id = message.author_id and user.user_id = ?
            order by message.pub_date desc limit ?''',
            [profile_user['user_id'], PER_PAGE]), followed=followed,
            profile_user=profile_user)


@app.route('/<username>/follow')
def follow_user(username):
    """Adds the current user as follower of the given user."""
    if not g.user:
        abort(401)
    whom_id = get_user_id(username)
    if whom_id is None:
        abort(404)
    db = get_db()
    db.execute('insert into follower (who_id, whom_id) values (?, ?)',
              [session['user_id'], whom_id])
    db.commit()
    flash('You are now following "%s"' % username)
    return redirect(url_for('user_timeline', username=username))


@app.route('/<username>/unfollow')
def unfollow_user(username):
    """Removes the current user as follower of the given user."""
    if not g.user:
        abort(401)
    whom_id = get_user_id(username)
    if whom_id is None:
        abort(404)
    db = get_db()
    db.execute('delete from follower where who_id=? and whom_id=?',
              [session['user_id'], whom_id])
    db.commit()
    flash('You are no longer following "%s"' % username)
    return redirect(url_for('user_timeline', username=username))


@app.route('/add_message', methods=['POST'])
def add_message():
    """Registers a new message for the user."""
    if 'user_id' not in session:
        abort(401)
    if request.form['text']:
        db = get_db()
        db.execute('''insert into message (author_id, text, pub_date)
          values (?, ?, ?)''', (session['user_id'], request.form['text'],
                                int(time.time())))
        db.commit()
        flash('Your message was recorded')
    return redirect(url_for('timeline'))


@app.route('/login', methods=['GET', 'POST'])
def login():
    """Logs the user in."""
    if g.user:
        return redirect(url_for('timeline'))
    error = None
    if request.method == 'POST':
        user = query_db('''select * from user where
            username = ?''', [request.form['username']], one=True)
        if user is None:
            error = 'Invalid username'
        elif not check_password_hash(user['pw_hash'],
                                     request.form['password']):
            error = 'Invalid password'
        else:
            flash('You were logged in')
            session['user_id'] = user['user_id']
            return redirect(url_for('timeline'))
    return render_template('login.html', error=error)


@app.route('/register', methods=['GET', 'POST'])
def register():
    """Registers the user."""
    if g.user:
        return redirect(url_for('timeline'))
    error = None
    if request.method == 'POST':
        if not request.form['username']:
            error = 'You have to enter a username'
        elif not request.form['email'] or \
                 '@' not in request.form['email']:
            error = 'You have to enter a valid email address'
        elif not request.form['password']:
            error = 'You have to enter a password'
        elif request.form['password'] != request.form['password2']:
            error = 'The two passwords do not match'
        elif get_user_id(request.form['username']) is not None:
            error = 'The username is already taken'
        else:
            db = get_db()
            db.execute('''insert into user (
              username, email, pw_hash) values (?, ?, ?)''',
              [request.form['username'], request.form['email'],
               generate_password_hash(request.form['password'])])
            db.commit()
            flash('You were successfully registered and can login now')
            return redirect(url_for('login'))
    return render_template('register.html', error=error)


@app.route('/logout')
def logout():
    """Logs the user out."""
    flash('You were logged out')
    session.pop('user_id', None)
    return redirect(url_for('public_timeline'))


# add some filters to jinja
app.jinja_env.filters['datetimeformat'] = format_datetime
app.jinja_env.filters['gravatar'] = gravatar_url


if __name__ == '__main__':
    init_db()
    app.run('127.0.0.1', debug=True, port=5000, ssl_context=('xxx', 'xxx'))

drop table if exists user;
create table user (
  user_id integer primary key autoincrement,
  username text not null,
  email text not null,
  pw_hash text not null
);

drop table if exists follower;
create table follower (
  who_id integer,
  whom_id integer
);

drop table if exists message;
create table message (
  message_id integer primary key autoincrement,
  author_id integer not null,
  text text not null,
  pub_date integer
);


drop table if exists access_token;
create table access_token (
  user_id integer not null,
  access_token_text text not null
);

def init_db():
    """Creates the database tables."""
    with app.app_context():
        db = get_db()
        with app.open_resource('schema.sql', mode='r') as f:
            try:
                db.cursor().executescript(f.read())
            except sqlite3.OperationalError, msg:
                print msg
        db.commit()