Some recommendations when raising warnings and exceptions

[framunoz]

I have noticed that in several modules warnings and exceptions are being thrown in a very general way. For example:

• In the module ee_extra/QA/clouds.py you can find the following code:

    platformDict = _get_platform_STAC(x)

    if platformDict["platform"] not in list(lookup.keys()):
        warnings.warn("This platform is not supported for cloud masking.")
        return x

It could be changed to:

    platformDict = _get_platform_STAC(x)
    platform = platformDict["platform"]

    if platform not in list(lookup.keys()):
        warnings.warn(f"Platform {platform} is not supported for cloud masking.")
        return x

To make the message more descriptive. Moreover, all the code could be refactored by including the platform variable.

• In the ee_extra/STAC/utils.py module, if the args argument does not have a "system:id", then it would throw the exception at the end, but that would be very confusing to the client using this functionality. Also, throwing a generic Exception is not the best way to handle exceptions.

That said, for this module, I propose the following implementation:

import ...  # etc...

# New custom exceptions
class ElementWithoutIdException(Exception):
    """Raised when an element does not have an ID."""

    def __init__(self, elem):
        super().__init__("Element does not have an 'system:id'.")
        self.elem = elem

class PlatformNotSupportedError(Exception):
    """Raised when a platform is not supported."""

    def __init__(self, platform: str):
        super().__init__(f"Platform '{platform}' not supported.")
        self.platform = platform

def _get_platform_STAC(args: Union[ee.Image, ee.ImageCollection]) -> dict:
    ...

    # Line 25
    ID = args.get("system:id").getInfo()
    if ID is None:
        raise ElementWithoutIdException(args)

    ...

    # line 50
    if plt is None:
        raise PlatformNotSupportedError(plt)

    ...

These custom exceptions have the advantage of also including the elements that caused the exception to be thrown for use in exception handling. This code exemplifies this:

class CustomException(Exception):
    def __init__(self, arg):
        super().__init__(f"Look at this arg!: '{arg}'")
        self.arg = arg

try:
    raise CustomException("A dummy arg")
except CustomException as e:
    print(f"Now a know the arg: '{e.arg}'")
>>> Now a know the arg: 'A dummy arg'

If you wish, I can open a PR to include these new changes, and try to find some other cases that are out there. Have a happy day!