Hi @wyli ,

Here you use a global dictionary to store the supported format -> writers mapping, while in the image readers we store readers in LoadImage transform with its own supported formats, for example:
https://github.com/Project-MONAI/MONAI/blob/dev/monai/data/image_reader.py#L386

I am not very sure which way is better, the readers way is similar to the Chain of Responsibility design pattern, This global SUPPORTED_WRITERS may be not easy to maintain, especially in multi-threads cases, etc.
Maybe because I was Java / C++ developer before, I usually never use global variables even in python. I prefer to use class to implement complicated logic, because it can maintain self-contained local states. For example you implemented FolderLayout as a class instead of a function.
Glad to see your opinions.
@ericspod @rijobro What do you guys think?

Thanks in advance.

SUPPORTED_WRITERS is a module-level variable, it's not a global one. it's a global dict accessed without global keyword.. I believe it's a
very common design, for example, scikit-image and PIL used it in a similar way

• https://github.com/scikit-image/scikit-image/blob/ed642e2bc822f362504d24379dee94978d6fa9de/skimage/io/manage_plugins.py#L39
• https://github.com/python-pillow/Pillow/blob/f5fab326fac3481308fc22349b869b691826e313/src/PIL/Image.py#L195

OK, I am not sure whether it can work fine if calling SaveImage in multi-thread? I think all our non-random transforms are thread-safe now.

Thanks.