无法从其他文件夹导入 Python

我似乎无法让 Python 导入子文件夹中的模块。当我尝试从导入的模块创建类的实例，但导入本身成功时，我得到了错误。下面是我的目录结构:

Server
-server.py
-Models
--user.py

下面是 server.py 的内容:

from sys import path
from os import getcwd
path.append(getcwd() + "\\models") #Yes, i'm on windows
print path
import user


u=user.User() #error on this line

还有 user.py:

class User(Entity):
using_options(tablename='users')


username = Field(String(15))
password = Field(String(64))
email    = Field(String(50))
status   = Field(Integer)
created  = Field(DateTime)

错误是: AttributeError: ‘ module’对象没有属性‘ User’

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最佳答案

I believe you need to create a file called __init__.py in the Models directory so that python treats it as a module.

Then you can do:

from Models.user import User

You can include code in the __init__.py (for instance initialization code that a few different classes need) or leave it blank. But it must be there.

小开

You have to create __init__.py on the Models subfolder. The file may be empty. It defines a package.

Then you can do:

from Models.user import User

Read all about it in python tutorial, here.

There is also a good article about file organization of python projects here.

小开

You're missing __init__.py. From the Python tutorial:

The __init__.py files are required to make Python treat the directories as containing packages; this is done to prevent directories with a common name, such as string, from unintentionally hiding valid modules that occur later on the module search path. In the simplest case, __init__.py can just be an empty file, but it can also execute initialization code for the package or set the __all__ variable, described later.

Put an empty file named __init__.py in your Models directory, and all should be golden.

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import user

u=user.User() #error on this line

Because of the lack of __init__ mentioned above, you would expect an ImportError which would make the problem clearer.

You don't get one because 'user' is also an existing module in the standard library. Your import statement grabs that one and tries to find the User class inside it; that doesn't exist and only then do you get the error.

It is generally a good idea to make your import absolute:

import Server.Models.user

to avoid this kind of ambiguity. Indeed from Python 2.7 'import user' won't look relative to the current module at all.

If you really want relative imports, you can have them explicitly in Python 2.5 and up using the somewhat ugly syntax:

from .user import User
小开

The right way to import a module located on a parent folder, when you don't have a standard package structure, is:

import os, sys
CURRENT_DIR = os.path.dirname(os.path.abspath(__file__))
sys.path.append(os.path.dirname(CURRENT_DIR))

(you can merge the last two lines but this way is easier to understand).

This solution is cross-platform and is general enough to need not modify in other circumstances.

小开

how do you write out the parameters os.path.dirname.... command?

import os, sys
CURRENT_DIR = os.path.dirname(os.path.abspath(__file__))
sys.path.append(os.path.dirname(CURRENT_DIR))
小开

My preferred way is to have __init__.py on every directory that contains modules that get used by other modules, and in the entry point, override sys.path as below:

def get_path(ss):
return os.path.join(os.path.dirname(__file__), ss)
sys.path += [
get_path('Server'),
get_path('Models')
]

This makes the files in specified directories visible for import, and I can import user from Server.py.

小开

After going through the answers given by these contributors above - Zorglub29, Tom, Mark, Aaron McMillin, lucasamaral, JoeyZhao, Kjeld Flarup, Procyclinsur, martin.zaenker, tooty44 and debugging the issue that I was facing I found out a different use case due to which I was facing this issue. Hence adding my observations below for anybody's reference.

In my code I had a cyclic import of classes. For example:

src
|-- utilities.py (has Utilities class that uses Event class)
|-- consume_utilities.py (has Event class that uses Utilities class)
|-- tests
|-- test_consume_utilities.py (executes test cases that involves Event class)

I got following error when I tried to execute python -m pytest tests/test_utilities.py for executing UTs written in test_utilities.py.

ImportError while importing test module '/Users/.../src/tests/test_utilities.py'.
Hint: make sure your test modules/packages have valid Python names.
Traceback:
tests/test_utilities.py:1: in <module>
from utilities import Utilities
...
...
E   ImportError: cannot import name 'Utilities'

The way I resolved the error was by re-factoring my code to move the functionality in cyclic import class so that I could remove the cyclic import of classes.

Note, I have __init__.py file in my 'src' folder as well as 'tests' folder and still was able to get rid of the 'ImportError' just by re-factoring the code.

Following stackoverflow link provides much more details on Circular dependency in Python.


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