def load(obj, env=None, silent=True, key=None, filename=None):
    """
    Reads and loads in to "obj" a single key or all keys from source
    :param obj: the settings instance
    :param env: settings current env (upper case) default='DEVELOPMENT'
    :param silent: if errors should raise
    :param key: if defined load a single key, else load all from `env`
    :param filename: Custom filename to load (useful for tests)
    :return: None
    """
    # Load data from your custom data source (file, database, memory etc)
    # use `obj.set(key, value)` or `obj.update(dict)` to load data
    # use `obj.find_file('filename.ext')` to find the file in search tree
    # Return nothing

    # This loader reads the .sff file // Stupid File Format
    keys = []
    values = []
    found_file = obj.find_file("settings.sff")
    if not found_file:
        return

    with open(found_file) as settings_file:
        for line in settings_file.readlines():
            if line.startswith("#"):
                continue
            if line.startswith("KEYS:"):
                keys = line.strip("KEYS:").strip("\n").split(";")
            if line.startswith("VALUES:"):
                values = line.strip("VALUES:").strip("\n").split(";")

    # // PLEASE DON'T USE THIS SFF file format :)

    data = dict(zip(keys, values))

    # support for inspecting data loaded by this loader
    source_metadata = SourceMetadata("sff", found_file, "default")

    if key:
        value = data.get(key.lower())  # sff format have lower case keys
        obj.set(key, value, loader_identifier=source_metadata)
    else:
        obj.update(data, loader_identifier=source_metadata)

    obj._loaded_files.append(found_file)

    Reads and loads in to "obj" a single key or all keys from source
    :param obj: the settings instance
    :param env: settings current env (upper case) default='DEVELOPMENT'
    :param silent: if errors should raise
    :param key: if defined load a single key, else load all from `env`
    :param filename: Custom filename to load (useful for tests)
    :return: None
    
tests_functional/legacy/custom_loader/my_custom_loader/sff_loader.py