[Tutor] Importing classes when needed

[Peter Otten]

Timo wrote:

> Hello all,
> 
> I have a question about how this is done the best way.
> 
> In my project I have a folder with multiple file parsers, like this:
> - src
>   -- main.py
>   -- parsers
>    --- __init__.py
>    --- parser1.py
>    --- parser2.py
> 
> The parsers just contain a class which do the work.
> 
> When the user clicks a button, I want to show all available parsers and
> use the choosen one when the user clicks "ok".
> Is it ok to place the following code in the __init__.py?
> from parser1 import Parser1
> from parser2 import Parser2
> def get_parsers():
>      return [Parser1(), Parser2()]
> 
> If so, is it ok to do a get_parsers() everytime the user clicks a
> button? Because that will initialize the parsers over and over again,
> right?

If you only need lazy instantiation, not lazy import, one solution is

from parser1 import Parser1
from parser2 import Parser2

_parsers = None

def get_parsers():
    global _parsers

    if _parsers is None:
        _parsers = [Parser1(), Parser2()]
    return _parsers