Feature request

Calling matplotlib.pyplot.show() displays all active figures. There are times this is not desirable, such as when some figure is still being developed. Of course, show() can be called for specific figures, but perhaps a user doesn't know that an undisplayed figure belongs to a class instance and these all get displayed when they call show() for their own plot.

Example at https://stackoverflow.com/q/59995448/4302578

It would be great if there was some attribute of a figure like figure.show_by_default, figure.implicit_show, or figure.exclude_from_show that could be set to stop these from popping up when plt.show() is called without arguments.