模块之间的导入问题

【问题标题】：importing issues between modules模块之间的导入问题
【发布时间】：2017-02-19 14:07:44
【问题描述】： 
|--------FlaskApp
|----------------FlaskApp
|----------------__init__.py
|----------------view.py
|----------------models.py
|----------------db_create.py
|-----------------------static
|-----------------------templates
|-----------------------venv
|-----------------------__init__.py
|----------------flaskapp.wsgi

这是我的模块和文件夹布局，我在初始化时遇到了导入问题

db = sqlalchemy
我正在尝试将 db 导入到 views.py、models.py 和 db_create.py 但我收到各种导入错误，因为我现在没有以正确的方式导入 thr 我的问题是，如果我想将 db 导入到我指定的模块中，我将如何做到这一点而不会出现错误

部分导入db的代码

models.py

from FlaskApp import db

class UserInfo(db.Model):

__tablename_ = 'user_info'

id = db.Column(db.Integer, primary_key=True)
username = db.Column(db.String(80), unique=True)
email = db.Column(db.String(80), unique=True)
password = db.Column(db.String(100), nullable=False)
posts = relationship('UserPosts', backref='posts')

def __init__(self, username, email, password):
    self.username = username
    self.email = email
    self.password = password

def __repr__(self):
        return '{}-{}'.format(self.username, self.email)

views.py

from FlaskApp import db

@app.route('/')
@login_required     
def home():
    user = db.session.query(UserInfo).all()
    return render_template('home.html', user=user)

__init__.py

from flask_sqlalchemy import SQLAlchemy

db = SQLAlchemy(app)


tail /var/log/apache2/error.log
[Tue Oct 11 04:17:20.925573 2016] [wsgi:error] [pid 5049:tid 139870897813248] [client 174.58.31.189:55884] Traceback (most recent call last):, referer: http://localhost/
[Tue Oct 11 04:17:20.925618 2016] [wsgi:error] [pid 5049:tid 139870897813248] [client 174.58.31.189:55884]   File "/var/www/FlaskApp/flaskapp.wsgi", line 14, in <module>, referer: http://localhost/
[Tue Oct 11 04:17:20.925626 2016] [wsgi:error] [pid 5049:tid 139870897813248] [client 174.58.31.189:55884]     from FlaskApp import app as application, referer: http://localhost/
[Tue Oct 11 04:17:20.925638 2016] [wsgi:error] [pid 5049:tid 139870897813248] [client 174.58.31.189:55884]   File "/var/www/FlaskApp/FlaskApp/__init__.py", line 4, in <module>, referer: http://localhost/
[Tue Oct 11 04:17:20.925644 2016] [wsgi:error] [pid 5049:tid 139870897813248] [client 174.58.31.189:55884]     import FlaskApp.main, referer: http://localhost/
[Tue Oct 11 04:17:20.925653 2016] [wsgi:error] [pid 5049:tid 139870897813248] [client 174.58.31.189:55884]   File "/var/www/FlaskApp/FlaskApp/main.py", line 7, in <module>, referer: http://localhost/
[Tue Oct 11 04:17:20.925658 2016] [wsgi:error] [pid 5049:tid 139870897813248] [client 174.58.31.189:55884]     from models import UserInfo, referer: http://localhost/
[Tue Oct 11 04:17:20.925668 2016] [wsgi:error] [pid 5049:tid 139870897813248] [client 174.58.31.189:55884]   File "/var/www/FlaskApp/FlaskApp/models.py", line 2, in <module>, referer: http://localhost/
[Tue Oct 11 04:17:20.925673 2016] [wsgi:error] [pid 5049:tid 139870897813248] [client 174.58.31.189:55884]     from FlaskApp import db, referer: http://localhost/
[Tue Oct 11 04:17:20.925707 2016] [wsgi:error] [pid 5049:tid 139870897813248] [client 174.58.31.189:55884] ImportError: cannot import name 'db', referer: http://localhost/

我的目标不仅仅是解决一个错误，而是从现在开始能够以正确的方式导入

【问题讨论】：

  • 堆栈跟踪是什么？

标签： python flask flask-sqlalchemy python-3.5


【解决方案1】：

这实际上是 Flask 学习者最痛苦的时刻。基本上，您的 FlaskApp 依赖于 FlaskApp.main 然后 FlaskApp.models 然后回到 FlaskApp 这创建了循环依赖的完美案例。

通过将db 变量附加到__init__.py 中的app，这是我认为优雅和pythonic 的方式：

from flask_sqlalchemy import SQLAlchemy

db = SQLAlchemy(app)
app.db = db

with app.app_context():
    import FlaskApp.main

在main.py:

from flask import current_app as app
from .models import UserInfo


@app.route('/')
@login_required     
def home():
    user = app.db.session.query(UserInfo).all()
    return render_template('home.html', user=user)

在models.py:

from flask import current_app as app

db = app.db


class UserInfo(db.Model):

    __tablename_ = 'user_info'

    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(80), unique=True)
    email = db.Column(db.String(80), unique=True)
    password = db.Column(db.String(100), nullable=False)
    posts = relationship('UserPosts', backref='posts')

    def __init__(self, username, email, password):
        self.username = username
        self.email = email
        self.password = password

    def __repr__(self):
        return '{}-{}'.format(self.username, self.email)

然后您可以在应用程序的任何函数/方法中使用app.db 或current_app.db，而无需担心循环依赖。

【讨论】：

  • 我试试看
  • 如果我尝试使用懒惰的方式，我仍然无法在 models.py 中导入名称数据库，我不确定如何使用您的第二个建议
  • @quechon 我编辑了答案。忘记延迟加载方式，它实际上需要更多棘手的工作来加载模型。
【解决方案2】：

使用上述答案后得到这个

RuntimeError：在应用程序上下文之外工作。这通常意味着您尝试使用需要以某种方式与当前应用程序对象交互的功能。为了解决这个问题，使用 app.app_context() 设置应用程序上下文。有关详细信息，请参阅文档。
    tail -n 40 /var/log/apache2/error.log
[Wed Oct 12 00:20:02.315500 2016] [wsgi:error] [pid 19327:tid 139821662463744] [client 174.58.31.189:51784]     import FlaskApp.main
[Wed Oct 12 00:20:02.315510 2016] [wsgi:error] [pid 19327:tid 139821662463744] [client 174.58.31.189:51784]   File "/var/www/FlaskApp/FlaskApp/main.py", line 2, in <module>
[Wed Oct 12 00:20:02.315516 2016] [wsgi:error] [pid 19327:tid 139821662463744] [client 174.58.31.189:51784]     from .models import UserInfo
[Wed Oct 12 00:20:02.315526 2016] [wsgi:error] [pid 19327:tid 139821662463744] [client 174.58.31.189:51784]   File "/var/www/FlaskApp/FlaskApp/models.py", line 7, in <module>
[Wed Oct 12 00:20:02.315532 2016] [wsgi:error] [pid 19327:tid 139821662463744] [client 174.58.31.189:51784]     db = app.db
[Wed Oct 12 00:20:02.315542 2016] [wsgi:error] [pid 19327:tid 139821662463744] [client 174.58.31.189:51784]   File "/usr/local/lib/python3.5/dist-packages/werkzeug/local.py", line 343, in __getattr__
[Wed Oct 12 00:20:02.315547 2016] [wsgi:error] [pid 19327:tid 139821662463744] [client 174.58.31.189:51784]     return getattr(self._get_current_object(), name)
[Wed Oct 12 00:20:02.315557 2016] [wsgi:error] [pid 19327:tid 139821662463744] [client 174.58.31.189:51784]   File "/usr/local/lib/python3.5/dist-packages/werkzeug/local.py", line 302, in _get_current_object
[Wed Oct 12 00:20:02.315563 2016] [wsgi:error] [pid 19327:tid 139821662463744] [client 174.58.31.189:51784]     return self.__local()
[Wed Oct 12 00:20:02.315573 2016] [wsgi:error] [pid 19327:tid 139821662463744] [client 174.58.31.189:51784]   File "/usr/local/lib/python3.5/dist-packages/flask/globals.py", line 51, in _find_app
[Wed Oct 12 00:20:02.315579 2016] [wsgi:error] [pid 19327:tid 139821662463744] [client 174.58.31.189:51784]     raise RuntimeError(_app_ctx_err_msg)
[Wed Oct 12 00:20:02.315611 2016] [wsgi:error] [pid 19327:tid 139821662463744] [client 174.58.31.189:51784] RuntimeError: Working outside of application context.
[Wed Oct 12 00:20:02.315620 2016] [wsgi:error] [pid 19327:tid 139821662463744] [client 174.58.31.189:51784] 
[Wed Oct 12 00:20:02.315628 2016] [wsgi:error] [pid 19327:tid 139821662463744] [client 174.58.31.189:51784] This typically means that you attempted to use functionality that needed
[Wed Oct 12 00:20:02.315634 2016] [wsgi:error] [pid 19327:tid 139821662463744] [client 174.58.31.189:51784] to interface with the current application object in a way.  To solve
[Wed Oct 12 00:20:02.315641 2016] [wsgi:error] [pid 19327:tid 139821662463744] [client 174.58.31.189:51784] this set up an application context with app.app_context().  See the
[Wed Oct 12 00:20:02.315648 2016] [wsgi:error] [pid 19327:tid 139821662463744] [client 174.58.31.189:51784] documentation for more information.
[Wed Oct 12 00:20:02.813916 2016] [wsgi:error] [pid 19326:tid 139821670856448] [client 174.58.31.189:51786] mod_wsgi (pid=19326): Target WSGI script '/var/www/FlaskApp/flaskapp.wsgi' cannot be loaded as Python module., referer: http://localhost/
[Wed Oct 12 00:20:02.814030 2016] [wsgi:error] [pid 19326:tid 139821670856448] [client 174.58.31.189:51786] mod_wsgi (pid=19326): Exception occurred processing WSGI script '/var/www/FlaskApp/flaskapp.wsgi'., referer: http://localhost/
[Wed Oct 12 00:20:02.814917 2016] [wsgi:error] [pid 19326:tid 139821670856448] [client 174.58.31.189:51786] Traceback (most recent call last):, referer: http://localhost/
[Wed Oct 12 00:20:02.814972 2016] [wsgi:error] [pid 19326:tid 139821670856448] [client 174.58.31.189:51786]   File "/var/www/FlaskApp/flaskapp.wsgi", line 14, in <module>, referer: http://localhost/
[Wed Oct 12 00:20:02.814981 2016] [wsgi:error] [pid 19326:tid 139821670856448] [client 174.58.31.189:51786]     from FlaskApp import app as application, referer: http://localhost/
[Wed Oct 12 00:20:02.814993 2016] [wsgi:error] [pid 19326:tid 139821670856448] [client 174.58.31.189:51786]   File "/var/www/FlaskApp/FlaskApp/__init__.py", line 4, in <module>, referer: http://localhost/
[Wed Oct 12 00:20:02.814998 2016] [wsgi:error] [pid 19326:tid 139821670856448] [client 174.58.31.189:51786]     import FlaskApp.main, referer: http://localhost/
[Wed Oct 12 00:20:02.815008 2016] [wsgi:error] [pid 19326:tid 139821670856448] [client 174.58.31.189:51786]   File "/var/www/FlaskApp/FlaskApp/main.py", line 2, in <module>, referer: http://localhost/
[Wed Oct 12 00:20:02.815014 2016] [wsgi:error] [pid 19326:tid 139821670856448] [client 174.58.31.189:51786]     from .models import UserInfo, referer: http://localhost/
[Wed Oct 12 00:20:02.815024 2016] [wsgi:error] [pid 19326:tid 139821670856448] [client 174.58.31.189:51786]   File "/var/www/FlaskApp/FlaskApp/models.py", line 7, in <module>, referer: http://localhost/
[Wed Oct 12 00:20:02.815029 2016] [wsgi:error] [pid 19326:tid 139821670856448] [client 174.58.31.189:51786]     db = app.db, referer: http://localhost/
[Wed Oct 12 00:20:02.815040 2016] [wsgi:error] [pid 19326:tid 139821670856448] [client 174.58.31.189:51786]   File "/usr/local/lib/python3.5/dist-packages/werkzeug/local.py", line 343, in __getattr__, referer: http://localhost/
[Wed Oct 12 00:20:02.815046 2016] [wsgi:error] [pid 19326:tid 139821670856448] [client 174.58.31.189:51786]     return getattr(self._get_current_object(), name), referer: http://localhost/
[Wed Oct 12 00:20:02.815055 2016] [wsgi:error] [pid 19326:tid 139821670856448] [client 174.58.31.189:51786]   File "/usr/local/lib/python3.5/dist-packages/werkzeug/local.py", line 302, in _get_current_object, referer: http://localhost/
[Wed Oct 12 00:20:02.815061 2016] [wsgi:error] [pid 19326:tid 139821670856448] [client 174.58.31.189:51786]     return self.__local(), referer: http://localhost/
[Wed Oct 12 00:20:02.815071 2016] [wsgi:error] [pid 19326:tid 139821670856448] [client 174.58.31.189:51786]   File "/usr/local/lib/python3.5/dist-packages/flask/globals.py", line 51, in _find_app, referer: http://localhost/
[Wed Oct 12 00:20:02.815077 2016] [wsgi:error] [pid 19326:tid 139821670856448] [client 174.58.31.189:51786]     raise RuntimeError(_app_ctx_err_msg), referer: http://localhost/
[Wed Oct 12 00:20:02.815107 2016] [wsgi:error] [pid 19326:tid 139821670856448] [client 174.58.31.189:51786] RuntimeError: Working outside of application context., referer: http://localhost/
[Wed Oct 12 00:20:02.815114 2016] [wsgi:error] [pid 19326:tid 139821670856448] [client 174.58.31.189:51786] , referer: http://localhost/
[Wed Oct 12 00:20:02.815118 2016] [wsgi:error] [pid 19326:tid 139821670856448] [client 174.58.31.189:51786] This typically means that you attempted to use functionality that needed, referer: http://localhost/
[Wed Oct 12 00:20:02.815123 2016] [wsgi:error] [pid 19326:tid 139821670856448] [client 174.58.31.189:51786] to interface with the current application object in a way.  To solve, referer: http://localhost/
[Wed Oct 12 00:20:02.815139 2016] [wsgi:error] [pid 19326:tid 139821670856448] [client 174.58.31.189:51786] this set up an application context with app.app_context().  See the, referer: http://localhost/
[Wed Oct 12 00:20:02.815143 2016] [wsgi:error] [pid 19326:tid 139821670856448] [client 174.58.31.189:51786] documentation for more information., referer: http://localhost/

【讨论】：

  • 堆栈跟踪是什么？您需要将所有相关的导入放在app_context 中。如果没有更多信息，我无能为力。
  • 刚刚添加了堆栈跟踪
  • stacktrace 太短，不包含问题点。请确保日志结果以“Traceback（最近一次通话最后一次）”之类的内容开头。
  • 如何从 apache2 获得更长的文件
  • 使用tail -n 40 /var/log/apache2/error.log。命令中的“40”是行号。
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