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You can create a variable with global scope by initializing outside all the functions in a python program. And you can access the variable from anywhere in the python program.
We declare a variable global by using the keyword global before a variable. All variables have the scope of the block, where they are declared and defined in. They can only be used after the point of their declaration.
The __init__.py file makes Python treat directories containing it as modules. Furthermore, this is the first file to be loaded in a module, so you can use it to execute code that you want to run each time a module is loaded, or specify the submodules to be exported.
As shown below, global variables can be accessed by any class or method within a class by simply calling the variable's name. Global variables can also be accessed by multiple classes and methods at the same time.
You should be able to put them in __init__.py. This is done all the time.
mypackage/__init__.py:
MY_CONSTANT = 42
mypackage/mymodule.py:
from mypackage import MY_CONSTANT
print "my constant is", MY_CONSTANT
Then, import mymodule:
>>> from mypackage import mymodule
my constant is 42
Still, if you do have constants, it would be reasonable (best practices, probably) to put them in a separate module (constants.py, config.py, ...) and then if you want them in the package namespace, import them.
mypackage/__init__.py:
from mypackage.constants import *
Still, this doesn't automatically include the constants in the namespaces of the package modules. Each of the modules in the package will still have to import constants explicitly either from mypackage or from mypackage.constants.
You cannot do that. You will have to explicitely import your constants into each individual module's namespace. The best way to achieve this is to define your constants in a "config" module and import it everywhere you require it:
# mypackage/config.py
MY_CONST = 17
# mypackage/main.py
from mypackage.config import *
You can define global variables from anywhere, but it is a really bad idea. import the __builtin__ module and modify or add attributes to this modules, and suddenly you have new builtin constants or functions. In fact, when my application installs gettext, I get the _() function in all my modules, without importing anything. So this is possible, but of course only for Application-type projects, not for reusable packages or modules.
And I guess no one would recommend this practice anyway. What's wrong with a namespace? Said application has the version module, so that I have "global" variables available like version.VERSION, version.PACKAGE_NAME etc.
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