Simple cross import in python

Question

I want to separate code in different class and put them to different files. However those class are dependent on each other.

main.py:

from lib import A, B  def main():     a = A()     b = B()     a.hello()     b.hello()  if __name__ == '__main__':     main() 

lib/_init_.py:

from a import A from b import B 

lib/a.py:

import lib.B  class A():     def __init__(self):         print "A"      def hello(self):         print "hello A"         b = B() 

lib/b.py:

import lib.A  class B():     def __init__(self):         print "B"      def hello(self):         print "hello B"         a = A() 

Is it possible to do that in Python?

EDIT:

I get this error message:

pydev debugger: starting Traceback (most recent call last):   File "eclipse-python/plugins/org.python.pydev_2.7.1.2012100913/pysrc/pydevd.py", line 1397, in <module>     debugger.run(setup['file'], None, None)   File "eclipse-python/plugins/org.python.pydev_2.7.1.2012100913/pysrc/pydevd.py", line 1090, in run     pydev_imports.execfile(file, globals, locals) #execute the script   File "main.py", line 2, in <module>     from lib import A, B   File "lib/__init__.py", line 1, in <module>     from a import A   File "lib/a.py", line 1, in <module>     import lib.B ImportError: No module named B 

Answer 1

Instead of importing the modules on top, you could import the other module within the hello function.

class B():     def __init__(self):         print "B"      def hello(self):         from lib import A         print "hello B"         a = A() 

Answer 2

When you have two classes depending on each other usually means that either they really belong to the same module or that you have a too tight coupling that should be resolved using dependency injection.

Now there are indeed a couple corner cases where importing from within the function is the "least worst" solution but that's still something you should avoid as much as possible.