在python包中使用另一个文件中的类并在__init __（）中发生冲突

Question

I'm writing a python package (python 3.6) and have the following directory structure:

package/
|  __init__.py
|  fileA.py
|  fileB.py
|  tests/
|  |  __init__.py
|  |  test_classA.py
|  |  test_classB.py

Setup

My files have the following contents:

# package/fileA.py
from package import ClassB

def ClassA:
    def __init__(self):
        self.my_ClassB = ClassB()

-

# package/fileB.py
def ClassB:
    def __init__(self):
        self.foo = "bar"

-

# package/tests/test_classB.py
from package import ClassB

# <performs some unit tests here>

-

# package/tests/test_classA.py
from package import ClassA

# <performs some unit tests here>

-

# package/__init__.py
from .fileA import ClassA
from .fileB import ClassB

Circular importing

When I ran python test_classB.py , I get the following traceback error showing that I have circular import statements, which are not allowed by python. Note - the package is not literally called package and I have edited the Traceback to match the toy example above.

Traceback (most recent call last):
  File "package/tests/test_classB.py", line 2, in <module>
    from package import ClassB
  File "/anaconda/lib/python3.5/site-packages/package/__init__.py", line 2, in <module>
    from .fileA import ClassA
  File "/anaconda/lib/python3.5/site-packages/package/merparse.py", line 2, in <module>
    from package import ClassB
ImportError: cannot import name 'ClassB'

Correcting the error

However, when I remove those two lines in my package/__init__.py file:

# package/__init__.py
from .fileA import ClassA
from .fileB import ClassB

...and I change the import method for package/fileA.py :

# package/fileA.py
from package.fileB import ClassB

def ClassA:
    def __init__(self):
        self.my_ClassB = ClassB()

... package/tests/test_classB.py runs correctly.

My Question

My question is: How can I keep the one file: one class structure in my files and import with from package import ClassA instead of having to import with from package.fileA import ClassA ?

In my package I would like to import classes from other files, but don't know how to get around circular importing.

Edit: Solution

Thanks to @mirandak and @martin-kalcok below for their help.

The only file that I had to edit was fileA.py to not refer to the package name in the import statement.

# package/fileA.py
from .fileB import ClassB

def ClassA:
    def __init__(self):
        self.my_ClassB = ClassB()

The package/__init__.py file still contains import statements in case I want to import the package from other scripts in the future that I don't couple with the package.

# package/__init__.py
from .fileA import ClassA
from .fileB import ClassB

Answer 1

The problem is with package/fileA.py . It's both a part of package and calling the __init__.py file of package as it's imported - creating a circular dependency.

Can you change fileA.py to look like this?

# package/fileA.py
from .fileB import ClassB

def ClassA:
    def __init__(self):
        self.my_ClassB = ClassB()

Answer 2

First of all, renaming your package to literary "package" really confuses this whole situation, but here's my take on it :D.
I don't think you are dealing with circular dependency, python just states that it cannot import classB from package and that is because there is no file named classB in package directory. Changing import statement to

from package.fileB import ClassB

works because there is directory package which contains file fileB which contains object ClassB .
To answer your question whether you can import classes with statement

from package import ClassB

you can't, unless your package is file and classB is object inside this file. However i don't see how this different import statement would be a dealbraker
Side Note : Your objects ClassB and ClassA are not classes, they are functions. Python uses keyword class to create classes and def to define functions.
Side note 2 : Are you sure your __init__.py file needs to hold any code at all?
Personal Note : I know that keeping 1 File / 1 Class structure is matter of personal preferences, it is not required in python and I myself find it much more comfortable to group multiple related classes and functions into one file