creating garbage collectable objects (caching objects)

[News123]

Hi.

I started playing with PIL.

I'm performing operations on multiple images and would like compromise
between speed and memory requirement.

The fast approach would load all images upfront and create then multiple
result files. The problem is, that I do not have enough memory to load
all files.

The slow approach is to load each potential source file only when it is
needed and to release it immediately after (leaving it up to the gc to
free memory when needed)



The question, that I have is whether there is any way to tell python,
that certain objects could be garbage collected if needed and ask python
at a later time whether the object has been collected so far (image has
to be reloaded) or not (image would not have to be reloaded)


# Fastest approach:
imgs = {}
for fname in all_image_files:
    imgs[fname] = Image.open(fname)
for creation_rule in all_creation_rules():
    img = Image.new(...)
    for img_file in creation_rule.input_files():
	img = do_somethingwith(img,imgs[img_file])
    img.save()


# Slowest approach:
for creation_rule in all_creation_rules():
    img = Image.new(...)
    for img_file in creation_rule.input_files():
        src_img = Image.open(img_file)
	img = do_somethingwith(img,src_img)
    img.save()



# What I'd like to do is something like:
imgs = GarbageCollectable_dict()
for creation_rule in all_creation_rules():
    img = Image.new(...)
    for img_file in creation_rule.input_files():
        if src_img in imgs: # if 'm lucke the object is still there
		src_img = imgs[img_file]
        else:
        	src_img = Image.open(img_file)
	img = do_somethingwith(img,src_img)
    img.save()



Is this possible?

Thaks in advance for an answer or any other ideas of
how I could do smart caching without hogging all the system's
memory