6

Is it bad practice to initialize the objects in the module, in the module code?

in Module.py:

class _Foo(object):
    def __init__(self):
        self.x = 'Foo'

Foo = _Foo()

Than in user code, you could:

>>> from Module import Foo
>>> print Foo.x
'Foo'
>>>

...without having to initialize the Foo class in the user code. Of course, only useful if you don't need arguments to initialize the object.

Is there a reason not to do this?

tMC
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  • you can use `@staticmethod` and class variables if you only need one instance – JBernardo Sep 13 '11 at 01:20
  • @JBernardo You can't use `staticmethod` and class variables, you can use `classmethod` and class variables. That's a poor way to create a singleton though. – agf Sep 13 '11 at 02:32
  • @agf I know it looks like the java's (bad) way of life... but it's not so bad. – JBernardo Sep 13 '11 at 02:39
  • You still mess up subclassing if you refer to the class by name from `staticmethod`s instead of using the automatically passed reference to the class from `classmethod`s. – agf Sep 13 '11 at 02:42

2 Answers2

7

Typically, you only want to run the minimum necessary to have your module usable. This will have an overall effect on performance (loading time), and can also make debugging easier.
Also, usually more than one instance will be created from any given class.

Having said that, if you have good reasons (such as only wanting one instance of a class), then certainly initialize it at load time.

Ethan Furman
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4

I do this sometimes, when it's really convenient, but I tend to do foo = Foo(). I really dislike the idea of making the class appear private, and making the instance available as Foo. As a developer using your code I'd find that pretty disconcerting.

Zach Kelling
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    Even if for some reason you really _do_ want the class to be private, you still should just lowercase for the instance name. – agf Sep 13 '11 at 02:34
  • Yes, because following [PEP8](http://www.python.org/dev/peps/pep-0008/) makes other Python developer's brains hurt less. – Zach Kelling Sep 13 '11 at 02:50