function exception.py

class Command:
	def redo(self, **kwargs):
		abstract

	def undo(self, **kwargs);
		abstract

class UploadImgurCommand extend Command:
	def redo(self, **kwargs):
		image = kwargs['image'];
		try:
			return imgurApi.upload(image);
		catch Exception as ex:
			throw ex;

	def undo(self, **kwargs):
		whatever		

class InsertToMangoCommand extend Command:
	def redo(self, **kwargs):
		image_url = kwargs['image_url']
		try:
			return mongoApi.insert(image_url);
		catch Exception as ex:
			throw ex;

class YourApplication:
	def upload_image(self, image):
		command_classes = [UploadImgurCommand, InsertToMangoCommand];
		args = { image: image }
		command_index = 1
		for command_class in command_classes:
			command = command_class(args);
			try:
				args = command.redo(args)
			catch Exception as ex:
				whatever