Import instance of class from a different module

Question

I have a module named directory and another module named species. There will always only be one directory no matter how many species i have.

In the directory module

Answer 1

Trying to answer this question, if I understand you correctly: how do I keep a global atlas for all my species, an example of the Singleton pattern? See this SO question.

One way of doing this, simply, and Pythonically, is to have module in a file directory.py that contains all the directory-related code and a global atlas variable:

atlas = []

def add_to_world(obj, space=[0,0]):
    species = {'obj' : obj.object_species,
               'name' : obj.name,
               'zone' : obj.zone,
               'space' : space}
    atlas.append( species )

def remove_from_world(obj):
    global atlas
    atlas = [ species for species in atlas
              if species['name'] != obj.name ]

# Add here functions to manipulate the world in the directory

Then in your main script the different species could reference that global atlas by importing the directory module, thus:

import directory

class Species(object):
    def __init__(self, object_species, name, zone = 'forest'):
        self.object_species = object_species
        self.name = name
        self.zone = zone
        directory.add_to_world(self)

class Llama(Species):
    def __init__(self, name):
        super(Llama, self).__init__('Llama', name)

class Horse(Species):
    def __init__(self, name):
        super(Horse, self).__init__('Horse', name, zone = 'stable')


if __name__ == '__main__':
    a1 = Llama(name='LL1')
    print directory.atlas
    # [{'obj': 'Llama', 'name': 'LL1', 'zone': 'forest', 'space': [0, 0]}]


    a2 = Horse(name='H2')
    print directory.atlas
    # [{'obj': 'Llama', 'name': 'LL1', 'zone': 'forest', 'space': [0, 0]},
    #  {'obj': 'Horse', 'name': 'H2', 'zone': 'stable', 'space': [0, 0]}]

    directory.remove_from_world(a1)
    print directory.atlas
    # [{'obj': 'Horse', 'name': 'H2', 'zone': 'stable', 'space': [0, 0]}]

The code can be much improved, but the general principles should be clear.