def _is_primary(s):
    """Indicates whether a sequence is a part of the primary assembly.

    Args:
        s (dict): A dictionary of sequence data, e.g. those in assembly['sequences'].
        
    Returns:
        bool: True if the sequence is part of the primary assembly, False otherwise.
    

    Examples:
        >>> _is_primary({'assembly_unit': 'Primary Assembly'})
        True
        
        >>> _is_primary({'assembly_unit': 'Something else entirely'})
        False
    """

    return s['assembly_unit'] == 'Primary Assembly'