Question

我在工作区中有工作空间和任务蓝图，工作空间视图工作空间/ apis.py和任务视图任务/ apis.py

我想从workspace / apis.py中的Task模型导入Task类，但我不能。

工作区模型：

class Workspace(db.Model):
    __tablename__ = 'workspace'
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.Unicode(50), nullable=False)
    created_on = db.Column(db.DateTime, default=datetime.utcnow)
    users = db.relationship('User', secondary=workspace_users,
                        backref=db.backref('workspaces', lazy='dynamic'),        lazy='dynamic')
    owners = db.relationship('User', secondary=workspace_owners,
                         backref=db.backref('own_workspaces', lazy='dynamic'), lazy='dynamic')
    teams = db.relationship('Team', cascade="all,delete", backref='workspace', lazy='dynamic')
    projects = db.relationship('Project', cascade="all,delete", backref='workspace', lazy='dynamic')
    tags = db.relationship('Tag', cascade="all,delete", backref='workspace', lazy='dynamic')
    user_costs = db.relationship('UserRate', backref='workspace', lazy='dynamic')
    clients = db.relationship('Client', backref='workspace', lazy='dynamic')

和任务模型：

class Task(db.Model):
    __tablename__ = 'task'
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.Unicode(120), nullable=False)
    start_time = db.Column(db.DateTime, default=datetime.datetime.utcnow)
    end_time = db.Column(db.DateTime)
    second = db.Column(db.Integer)
    rate = db.Column(db.Float)
    status = db.Column(db.Boolean, default=True)
    project_id = db.Column(db.Integer, db.ForeignKey('project.id'))
    owner_id = db.Column(db.Integer, db.ForeignKey('user.id'))
    tags = db.relationship('Tag', secondary=task_tag,
                           backref=db.backref('tasks', lazy='dynamic'), lazy='dynamic')

在任务视图中我可以导入Workspace类，但在工作区视图中我无法导入任务类。

错误：

Traceback (most recent call last):
  File "./run.py", line 8, in <module>
    from project.application import create_app, db
  File "/home/itmard/git/toggle-dev/project/__init__.py", line 1, in <module>
    from project.application import create_app
  File "/home/itmard/git/toggle-dev/project/application.py", line 5, in <module>
    from project.apps.task.models import calculate_user_rate
  File "/home/itmard/git/toggle-dev/project/apps/task/__init__.py", line 12, in <module>
    from . import apis
  File "/home/itmard/git/toggle-dev/project/apps/task/apis.py", line 12, in <module>
    from project.apps.task.models import Task
  File "/home/itmard/git/toggle-dev/project/apps/task/models.py", line 7, in <module>
    from project.apps.user_rate.models import UserRate
  File "/home/itmard/git/toggle-dev/project/apps/user_rate/__init__.py", line 8, in <module>
    from . import views
  File "/home/itmard/git/toggle-dev/project/apps/user_rate/views.py", line 10, in <module>
    from project.apps.user_rate.forms import AddUserRateForm
  File "/home/itmard/git/toggle-dev/project/apps/user_rate/forms.py", line 11, in <module>
    from project.apps.workspace.models import workspaces
  File "/home/itmard/git/toggle-dev/project/apps/workspace/__init__.py", line 12, in <module>
    from . import apis
  File "/home/itmard/git/toggle-dev/project/apps/workspace/apis.py", line 12, in <module>
    from project.apps.task.models import Task
ImportError: cannot import name Task

项目结构：

├── project
│   ├── application.py
│   ├── apps
│   │   ├── task
│   │   │   ├── apis.py
│   │   │   ├── forms.py
│   │   │   ├── __init__.py
│   │   │   ├── __init__.py~
│   │   │   ├── models.py
│   │   │   └── views.py
│   │   └── workspace
│   │       ├── apis.py
│   │       ├── forms.py
│   │       ├── __init__.py
│   │       ├── models.py
│   │       └── views.py

Answer 1

考虑以下情况：

main.py

from a import whats_up
print whats_up()

模块a：

first = 1
from b import second
third = 3
def whats_up():
    return first + second + third

模块b：

second = 2
from a import first
print first
from a import third
print third

此代码遇到同样的问题。

模块a在导入时会为其创建一个对象。然后，它将first分配给该对象。接下来，Python将开始导入模块b。请注意，我们尚未向模块third分配a！

加载模块b后，它会分配second，然后尝试从first导入a。这样成功，因此将打印1。然后，它会尝试从third导入a。这是发生错误的地方：a从未将其加载到定义third的位置。

现在让我们看看你的堆栈跟踪：

您的追溯如下所示：

Traceback (most recent call last):
  File "./run.py", line 8, in <module>
    from project.application import create_app, db
  File "/home/itmard/git/toggle-dev/project/__init__.py", line 1, in <module>
    from project.application import create_app
  File "/home/itmard/git/toggle-dev/project/application.py", line 5, in <module>
    from project.apps.task.models import calculate_user_rate
  File "/home/itmard/git/toggle-dev/project/apps/task/__init__.py", line 12, in <module>
    from . import apis
  File "/home/itmard/git/toggle-dev/project/apps/task/apis.py", line 12, in <module>
    from project.apps.task.models import Task
  ...
  File "/home/itmard/git/toggle-dev/project/apps/user_rate/forms.py", line 11, in <module>
    from project.apps.workspace.models import workspaces
  File "/home/itmard/git/toggle-dev/project/apps/workspace/__init__.py", line 12, in <module>
    from . import apis
  File "/home/itmard/git/toggle-dev/project/apps/workspace/apis.py", line 12, in    <module>
    from project.apps.task.models import Task

请注意...之前的部分：此时，正在导入tasks.models模块。但是，在第7行，您可以这样做：

from project.apps.user_rate.models import UserRate

在完全定义Task模型之前，您开始加载user_rate.models模块，该模块本身有一堆定义，如果您遵循堆栈跟踪，则返回其中一个模块还试图导入apps.tasks.models。

这导致循环依赖性（例如，模块1依赖于模块2，模块2依赖于取决于模块1的模块3）。您需要重新思考模块如何相互依赖以解决此问题。

Flask导入错误

1 个答案: