How to do relative imports in Python?

asked16 years ago
last updated10 years ago
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Up Vote602Down Vote

Imagine this directory structure:

app/
   __init__.py
   sub1/
      __init__.py
      mod1.py
   sub2/
      __init__.py
      mod2.py

I'm coding mod1, and I need to import something from mod2. How should I do it?

I tried from ..sub2 import mod2 but I'm getting an "Attempted relative import in non-package".

I googled around but found only "sys.path manipulation" hacks. Isn't there a clean way?


Edit: all my __init__.py's are currently empty

Edit2: I'm trying to do this because sub2 contains classes that are shared across sub packages (sub1, subX, etc.).

Edit3: The behaviour I'm looking for is the same as described in PEP 366 (thanks John B)

12 Answers

Up Vote9Down Vote

Everyone seems to want to tell you what you should be doing rather than just answering the question.

The problem is that you're running the module as 'main' by passing the mod1.py as an argument to the interpreter.

From PEP 328:

Relative imports use a module's name attribute to determine that module's position in the package hierarchy. If the module's name does not contain any package information (e.g. it is set to 'main') then relative imports are resolved as if the module were a top level module, regardless of where the module is actually located on the file system.

In Python 2.6, they're adding the ability to reference modules relative to the main module. PEP 366 describes the change.

: According to Nick Coghlan, the recommended alternative is to run the module inside the package using the -m switch.

Up Vote9Down Vote
Grade: A

To import from another module in the same package using relative imports, you need to use the from .. import syntax.

However, your current directory structure does not match the requirements for relative imports. In order for a relative import to work, the modules must be located inside the same package, which means that they must be located under the same directory.

To achieve what you want, you need to modify your directory structure to include a package root directory and move the __init__.py files into it:

app/
   __init__.py
   sub1/
      __init__.py
      mod1.py
   sub2/
      __init__.py
      mod2.py
   shared/
      __init__.py
      class.py

Now, you can do relative imports from mod1 to class.py using the following code:

from ..shared import class

Note that the .. notation refers to the parent directory of the current module.

Alternatively, if you don't want to create a separate package for your shared classes, you can also use the importlib module to import modules from another directory:

import importlib

class = importlib.import_module('app.shared.class', __name__)

This approach allows you to import a module from any directory, but it may be less convenient than using relative imports in some cases.

Up Vote9Down Vote
Grade: A

Sure, here's a clean way to import something from mod2 in mod1 without using relative imports:

from sub2.mod2 import ClassFromMod2

# Alternatively:
import sub2.mod2

This code assumes that ClassFromMod2 is a class defined in the mod2 module.

Explanation:

  1. Relative imports are not recommended: PEP 366 discourages relative imports within a package, as it can lead to circular dependencies and confusion. Using absolute imports or the import statement with a clear path is a more robust and recommended approach.

  2. import sub2.mod2 is not valid: This is an attempted relative import. The correct path should be from sub2 import mod2.

  3. Using from ..sub2 import mod2 doesn't work: The .. notation in from ..sub2 import mod2 is not a standard way to specify a parent package. It might be causing a circular import error or not finding the module correctly.

By using the absolute path or from sub2 import mod2, you are explicitly telling the Python interpreter where to find the module. This ensures that the import is made correctly without getting the "Relative import in non-package" error.

Note:

  • Ensure that the __init__.py files in all sub packages are empty and have the correct permissions (readable and executable).
  • Use the fully qualified path to the module.
  • Make sure that the mod2 module is located within the same package or in a sub package within your project.

By using these techniques, you can successfully import from mod2 within mod1 without resorting to relative imports.

Up Vote8Down Vote
Grade: B

In Python, when you want to perform relative imports from within a package, the module must be packaged correctly. That means, your package directory structure should look like this :

app/
    __init__.py
    sub1/
        __init__.py
        mod1.py
    sub2/
        __init__.py
        mod2.py

This is how your code might look:

from .sub2 import mod2

The dot (.) means that the current package is being referred to. Without the dot, you would need to specify app.sub2 if running as a main script in an app directory. This will work as long as both directories are properly added to your pythonpath or init.py files exist in sub1 and sub2.

You do not have to worry about sys path manipulation, unless you need something very specific and it's related to this import system rather than the packaging of modules itself.

This is all covered in PEP 366 as well: https://www.python.org/dev/peps/pep-0366/. This feature allows for a way to reference relative paths with ease and avoids the issues of sys path manipulation that could otherwise occur if not correctly configured, like you are seeing.

If you have an __init__.py file in both sub1 and sub2 directory, Python will treat them as packages, thus allowing for proper relative imports from mod1 to mod2.

For instance:

#sub1/mod1.py
from .sub2 import mod2

def func():
    print("this is function in mod1")

func()
mod2.func()

And __init__.py file of sub2 would be like :

#sub2/__init__.py

def func():
    print("This is a module from sub 2 in package app")

Both mod1 and mod2 will import each other without any error about relative paths or sys path manipulation. Just make sure the directory structure as I mentioned above exists where necessary for correct packaging of Python packages to work properly for imports.

Up Vote8Down Vote
Grade: B

To enable relative imports, you must have an __init__.py file in every directory that might contain submodules.

In your case, the directory structure is:

app/
   __init__.py
   sub1/
      __init__.py
      mod1.py
   sub2/
      __init__.py
      mod2.py

So in this case, you need to create __init__.py files in the directories app and sub1.

Once you have done that, you can import mod2 from mod1 using the following code:

from ..sub2 import mod2

This will work because the __init__.py files in the app and sub1 directories will add the app and sub1 directories to the Python path, allowing you to import modules from those directories using relative imports.

Up Vote8Down Vote
Grade: B

It seems like you're trying to perform a relative import across packages, which is causing the "Attempted relative import in non-package" error. This error occurs because Python doesn't recognize the current directory as a package when running the script directly.

To fix this issue, you can use the -m flag when running your script, which allows Python to treat the current directory as a package. Here's how you can do it:

  1. Open a terminal.
  2. Navigate to the app directory.
  3. Run the following command:
python -m sub1.mod1

Now, you should be able to use relative imports in your code:

from ..sub2 import mod2

However, since your __init__.py files are currently empty, you might encounter another error: "No module named 'sub2'". To fix this, you can add an import statement in your sub1/__init__.py file to import the mod1 module:

# sub1/__init__.py
from . import mod1

Similarly, add an import statement in your app/__init__.py file to import the sub1 package:

# app/__init__.py
from .sub1 import *

Now, you can run the script using the -m flag as mentioned earlier:

python -m app.sub1.mod1

With these changes, your relative imports should work as expected. This approach follows the recommendations in PEP 366.

Up Vote8Down Vote
Grade: B

Everyone seems to want to tell you what you should be doing rather than just answering the question.

The problem is that you're running the module as 'main' by passing the mod1.py as an argument to the interpreter.

From PEP 328:

Relative imports use a module's name attribute to determine that module's position in the package hierarchy. If the module's name does not contain any package information (e.g. it is set to 'main') then relative imports are resolved as if the module were a top level module, regardless of where the module is actually located on the file system.

In Python 2.6, they're adding the ability to reference modules relative to the main module. PEP 366 describes the change.

: According to Nick Coghlan, the recommended alternative is to run the module inside the package using the -m switch.

Up Vote7Down Vote
Grade: B

To perform relative imports in the given directory structure, you should ensure that sub1 is recognized as a package first. This can be achieved by adding an empty __init__.py file in sub1. Here's how you can import mod2 from mod1:

from sub1.sub2 import mod2

Now, Python should recognize the package hierarchy and allow the relative import without issues.

The reason why your previous attempt failed was because in that case, you were trying to import a directory (sub2) rather than the module (mod2).

By making sure sub1 is recognized as a package with an empty __init__.py, the relative import path will work correctly.

Up Vote5Down Vote
Grade: C
from app.sub2 import mod2
Up Vote4Down Vote
Grade: C

For example, this is what I think your __init__.py file should look like:

import sys
sys.path[1].append('sub2')
from . import mod2 as module

def main():
    print(module)

The idea here is to manipulate the path for the current python process in order to access modules that are outside of its own package (which you can find under the 'init.py' files).
In this way, it would work with both a relative and absolute import in main() as well.

The logic behind these steps is as follows: Python first looks for an import mod2 as module. If that doesn't work, it then attempts to import the entire path up one directory (i.e., sys.path[1]). This should point to the "sub2" directory which contains your desired modules and therefore will allow you to import them.

If you want more advanced control over Python's import system or if your code is complex, then it would be good idea to read PEP 366 to learn more about the Python import mechanism in detail and consider using tools like setuptools, which allows you to build your packages with detailed setup instructions for installing all dependencies.

Answer: The main part of your main() function should look something like this (note that it will only work correctly if your init.py file is correct):

import sys  
sys.path[1].append('sub2') # Adding 'sub2' to the list of directories to be searched for modules in case you need an absolute import 
from . import mod2 as module # Importing 'mod2' as module from its directory, assuming it is at `sub2` dir  

def main():    # Assumed that this function runs on your package's __init__.py file 
   print(module)      # Prints the module with relative import  

This will ensure you can use relative imports as described in PEP 366 and it is a very flexible way to deal with Python's import mechanism.

Up Vote3Down Vote
Grade: C

In Python, relative imports work by using a module's directory path when trying to import its modules. To import something from mod2, you can use the following relative import statement:

from .sub2 import mod2

This statement tells Python that it should look for the mod2 module in the same directory as the current file (__name__.py). Once Python finds the mod2 module, it will automatically import any of its modules into the current file (__name__.py)). In this particular example, you can use the following relative import statement to import the math.sqrt() function from within the sub1 package:

import numpy as np  # Import a different module (numpy) here.
from sub1.subX import mod2

print(np.sqrt(2))) # Use the imported `sqrt(2)` function here.
Up Vote0Down Vote
Grade: F

Sure, here's how you can do relative imports in Python in your specific situation:

from app.sub2.mod2 import MyClass

# Now you can use the `MyClass` class from `mod2`
print(MyClass)

Explanation:

  • Your current directory is mod1, so you need to navigate up two levels to reach the mod2 module.
  • The from app.sub2 import mod2 syntax is correct, but you need to ensure that the __init__.py files in each directory are present and empty.
  • If you have empty __init__.py files in all directories, Python will search for the module in the current directory first, and then move up the directory tree until it finds the module.

Additional Notes:

  • Make sure that all your __init__.py files are empty. If they contain any code, it may cause unexpected behavior.
  • If you are trying to import a class from a module in a sub-package, you need to use the from app.sub2.mod2 import MyClass syntax.
  • You can find more information about PEP 366 and relative imports in the official Python documentation.

EDIT:

  • You've edited your original post to include more information about your directory structure and your goal. This makes it much easier for me to understand your problem and provide a solution.

EDIT 2:

  • You've clarified that you want to share classes across sub-packages. This is a common use case for relative imports.

EDIT 3:

  • You've referenced PEP 366, which describes the official guidelines for relative imports in Python. This is helpful because it ensures that you are using the correct syntax and understanding the underlying principles.