This already exists as `warnings.DeprecationWarning` see the documentation here:
> Base category for warnings about deprecated features when those warnings are intended for other Python developers (ignored by default, unless triggered by code in `__main__`).
..makes it almost useless for most. Going back to your original suggestion though, having some decorator similar to NodeJs `util.deprecate` (which only prints the warning once) would be very convenient and much easier detected by editors and linters.