Solving problem is about exposing yourself to as many situations as possible like How to do relative imports in Python? and practice these strategies over and over. With time, it becomes second nature and a natural way you approach any problems in general. Big or small, always start with a plan, use other strategies mentioned here till you are confident and ready to code the solution.
In this post, my aim is to share an overview the topic about How to do relative imports in Python?, which can be followed any time. Take easy to follow this discuss.
Imagine this directory structure:
app/ __init__.py sub1/ __init__.py mod1.py sub2/ __init__.py mod2.py
mod1, and I need to import something from
mod2. How should I do it?
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 (
Edit3: The behaviour I’m looking for is the same as described in PEP 366 (thanks John 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.
Update: According to Nick Coghlan, the recommended alternative is to run the module inside the package using the -m switch.
Here is the solution which works for me:
I do the relative imports as
from ..sub2 import mod2
and then, if I want to run
mod1.py then I go to the parent directory of
app and run the module using the python -m switch as
python -m app.sub1.mod1.
The real reason why this problem occurs with relative imports, is that relative imports works by taking the
__name__ property of the module. If the module is being directly run, then
__name__ is set to
__main__ and it doesn’t contain any information about package structure. And, thats why python complains about the
relative import in non-package error.
So, by using the -m switch you provide the package structure information to python, through which it can resolve the relative imports successfully.
I have encountered this problem many times while doing relative imports. And, after reading all the previous answers, I was still not able to figure out how to solve it, in a clean way, without needing to put boilerplate code in all files. (Though some of the comments were really helpful, thanks to @ncoghlan and @XiongChiamiov)
Hope this helps someone who is fighting with relative imports problem, because going through PEP is really not fun.
main.py setup.py app/ -> __init__.py package_a/ -> __init__.py module_a.py package_b/ -> __init__.py module_b.py
- You run
Alternatively 2 or 3 could use:
from app.package_a import module_a
That will work as long as you have
app in your PYTHONPATH.
main.py could be anywhere then.
So you write a
setup.py to copy (install) the whole app package and subpackages to the target system’s python folders, and
main.py to target system’s script folders.
“Guido views running scripts within a package as an anti-pattern” (rejected
I have spent so much time trying to find a solution, reading related posts here on Stack Overflow and saying to myself “there must be a better way!”. Looks like there is not.
This is solved 100%:
Import settings/local_setting.py in app/main.py:
import sys sys.path.insert(0, "../settings") try: from local_settings import * except ImportError: print('No Import')
def import_path(fullpath): """ Import a file with full path specification. Allows one to import from anywhere, something __import__ does not do. """ path, filename = os.path.split(fullpath) filename, ext = os.path.splitext(filename) sys.path.append(path) module = __import__(filename) reload(module) # Might be out of date del sys.path[-1] return module
I’m using this snippet to import modules from paths, hope that helps
nosklo's answer with examples
__init__.py files are empty.
main.py app/ -> __init__.py package_a/ -> __init__.py fun_a.py package_b/ -> __init__.py fun_b.py
def print_a(): print 'This is a function in dir package_a'
from app.package_a.fun_a import print_a def print_b(): print 'This is a function in dir package_b' print 'going to call a function in dir package_a' print '-'*30 print_a()
from app.package_b import fun_b fun_b.print_b()
if you run
$ python main.py it returns:
This is a function in dir package_b going to call a function in dir package_a ------------------------------ This is a function in dir package_a
- main.py does:
from app.package_b import fun_b
- fun_b.py does
from app.package_a.fun_a import print_a
so file in folder
package_b used file in folder
package_a, which is what you want. Right??
This is unfortunately a sys.path hack, but it works quite well.
I encountered this problem with another layer: I already had a module of the specified name, but it was the wrong module.
what I wanted to do was the following (the module I was working from was module3):
mymodule __init__.py mymodule1 __init__.py mymodule1_1 mymodule2 __init__.py mymodule2_1 import mymodule.mymodule1.mymodule1_1
Note that I have already installed mymodule, but in my installation I do not have “mymodule1”
and I would get an ImportError because it was trying to import from my installed modules.
I tried to do a sys.path.append, and that didn’t work. What did work was a sys.path.insert
if __name__ == '__main__': sys.path.insert(0, '../..')
So kind of a hack, but got it all to work!
So keep in mind, if you want your decision to override other paths then you need to use sys.path.insert(0, pathname) to get it to work! This was a very frustrating sticking point for me, allot of people say to use the “append” function to sys.path, but that doesn’t work if you already have a module defined (I find it very strange behavior)