''' Purpose: do some functions produces lists from a string
'''

def separate( s ) :
    ''' Returns a new list where each element in the list corresponds to a character of s
    '''

    pass

def join( sl ) :
    ''' Returns a string composed of the strings in string list sl, where a blank is used
        to separate the strings from each other.
    '''

    pass

def ints( ns ) :
    ''' Returns list of integers corresponding to the integer substrings in ns.
    '''

    pass
        
def parse_phone_string( pn ) :
    ''' Returns a three-element integer list. The first element of the list is the pn area code,
        the middle element of the list is the pn prefix; the last element is the pn line number
    '''

    pass