def to_list(data_in):
    """Convert the data into a list. Does not pack lists into a new one.

    If your input is, for example, a string or a list of strings, or a
    tuple filled with strings, you have, in general, a problem:

    - just iterate through the object will fail because it iterates through the
      characters of the string.
    - using list(obj) converts the tuple, leaves the list but splits the strings
      characters into single elements of a new list.
    - using [obj] creates a list containing a string, but also a list containing
      a list or a tuple, which you did not want to.

    Solution: use to_list(obj), which creates a new list in case the object is
    a single object (a string is a single object in this sence) or converts
    to a list if the object is already a container for several objects.

    Parameters
    ----------
    data_in : any obj
        So far, any object can be entered.

    Returns
    -------
    out : list
        Return a list containing the object or the object converted to a list.
    """
    if isinstance(data_in, (str, int, float)):
        data_in = [data_in]
    data_in = list(data_in)
    return data_in