OO conventions

[Steve Holden]

Daniel Nogradi wrote:
[...]
> So after all, what is a 'factory' or 'factory function'?

The name is intended to be indicative: it's a function that makes things 
- usually instances of some class.

As has already been pointed out. Image is a module from PIL, so 
Image.open() is a function in that module. When you call it, it creates 
an instance of some suitable image class (which will depend on the type 
of the image) and returns that.

The point here is that Image.open() returns a 
JpegImagePlugin.JpegImageFile instance for a .jpg file, a 
GifImagePlugin.GifImageFile instance for a .gif file, and so on. It 
wouldn't make sense to use a single class to represent all these 
different image types, so Image.open() just creates an instance of the 
appropriate class (whatever that may be, which will vary from call to 
call) and returns that.

regards
  Steve
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