在django模型上导入错误

I wrote this funcion on a utils.py located on the app direcroty:

我写了这篇关于utils的文章。py位于app direcroty:

from bm.bmApp.models import Client

def get_client(user):
    try:
        client = Client.objects.get(username=user.username)
    except Client.DoesNotExist:
        print "User Does not Exist"
        return None
    else:       
        return client

def to_safe_uppercase(string):
    if string is None:
        return ''
    return string.upper()

Then when i use the function to_safe_uppercase on my models.py file, by importing it in this way:

然后当我在模型上使用to_safe_uppercase函数时。py文件，通过这种方式导入:

from bm.bmApp.utils import to_safe_uppercase 

I got the python error:

我得到了python错误:

     from bm.bmApp.utils import to_safe_uppercase
ImportError: cannot import name to_safe_uppercase

I got the solution for this problem when i change the import statement for:

当我将导入语句改为:

from bm.bmApp.utils import *

But i can't understand why is this, why when i import the specific function i got the error?

但是我不明白为什么，为什么当我导入特定的函数时我得到了错误?

3 个解决方案

#1

You are doing what is known as a Circular import.

您正在执行循环导入。

models.py:

models.py:

from bm.bmApp.utils import to_safe_uppercase

utils.py:

utils.py:

from bm.bmApp.models import Client

Now when you do import bm.bmApp.models The interpreter does the following:

现在当你导入bmapp的时候。模型译员做以下工作:

1. models.py - Line 1: try to import bm.bmApp.utils
2. 模型。py -第1行:尝试导入bm.bmApp.utils
3. utils.py - Line 1: try to import bm.bmApp.models
4. 跑龙套。py - Line 1:尝试导入bm.bmApp.models
5. models.py - Line 1: try to import bm.bmApp.utils
6. 模型。py -第1行:尝试导入bm.bmApp.utils
7. utils.py - Line 1: try to import bm.bmApp.models
8. 跑龙套。py - Line 1:尝试导入bm.bmApp.models
9. ...
10. …

The easiest solution is to move the import inside the function:

最简单的解决方案是将导入移动到函数内部:

utils.py:

utils.py:

def get_client(user):
    from bm.bmApp.models import Client
    try:
        client = Client.objects.get(username=user.username)
    except Client.DoesNotExist:
        print "User Does not Exist"
        return None
    else:       
        return client

def to_safe_uppercase(string):
    if string is None:
        return ''
    return string.upper()

#2

You are creating a circular import.

您正在创建循环导入。

utils.py
from bm.bmApp.models import Client
# Rest of the file...

models.py
from bm.bmApp.utils import to_safe_uppercase
# Rest of the file...

I would suggest your refactor your code so that you don't have a circular dependency (i.e. utils should not need to import models.py or vice versa).

我建议您重构代码，这样就不会有循环依赖(例如，utils不需要导入模型)。py,反之亦然)。

#3

I'm not sure I can explain the Import error, but I have three ideas. First, your function needs tweaking. You've used a reserved word 'string' as an argument. Consider renaming.

我不确定我能否解释导入错误，但我有三个想法。首先，您的功能需要调整。您使用了一个保留字'string'作为参数。考虑重命名。

Second, what happens if you invoke ./manage.py shell, and do the import by hand. Does it give you any different?

其次，如果您调用。/manage会发生什么。py shell，手工导入。有什么不同吗?

Third, try deleting your pyc files to force django to recompile python code (this one is a very long shot...but worth eliminating)

第三，尝试删除pyc文件以强制django重新编译python代码(这是一个很长的镜头……)但是值得消除)