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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:

def _is_path(instance, attribute, s, exists=True):
    "Validator for path-yness"
    if not s:
        # allow False as a default
        return
    if exists:
        if os.path.exists(s):
            return
        else:
            raise OSError("path does not exist")
    else:
        # how do we tell if it's a path if it doesn't exist?
        raise TypeError("Not a path?")