def mean(float_list):
    """Calcul and return the mean for the given list of numbers (float and int).

	If the list is emmpty or None, return None.
	Else, the value returned is a float."""
    if float_list is None or not float_list:
        return None
    if len(float_list) == 1:
        return float_list[0]
    sum = 0
    for number in float_list:
        sum += float(number)
    return sum / len(float_list)
