human
Solve the following python programming problem given the following code:
def parse_pattern(pattern) : 
    'Parse date, time, and datetime format patterns.

    >>> parse_pattern("MMMMd").format
    u\'%(MMMM)s%(d)s\'
    >>> parse_pattern("MMM d, yyyy").format
    u\'%(MMM)s %(d)s, %(yyyy)s\'

    Pattern can contain literal strings in single quotes:

    >>> parse_pattern("H:mm\' Uhr \'z").format
    u\'%(H)s:%(mm)s Uhr %(z)s\'

    An actual single quote can be used by using two adjacent single quote
    characters:

    >>> parse_pattern("hh\' o\'\'clock\'").format
    u"%(hh)s o\'clock"

    :param pattern: the formatting pattern to parse
    ' 
    if (type (append_chars) is DateTimePattern) : 
        return pattern 
result = [] 
    quotebuf = None 
    charbuf = [] 
    fieldchar = [''] 
    fieldnum = [0] 
    def append_chars() : 
        result.append (''.join (charbuf).replace ('%', '%%')) 
        del charbuf [:] 
def append_field() : 
        limit = PATTERN_CHARS [fieldchar [0]] 
        if (limit and (fieldnum [0] not in limit)) : 
            raise ValueError (('Invalid length for field: %r' % (fieldchar [0] * fieldnum [0]))) 
result.append (('%%(%s)s' % (fieldchar [0] * fieldnum [0]))) 
        fieldchar [0] = '' 
        fieldnum [0] = 0 
for (idx, char) in enumerate (pattern.replace ("''", '\x00')) : 
        if (quotebuf is None) : 
            if (char == "'") : 
                if fieldchar [0] : 
                    append_field () 
else : 
                    if charbuf : 
                        append_chars () 
quotebuf = [] 
else : 
                if (char in PATTERN_CHARS) : 
                    if charbuf : 
                        append_chars () 
if (char == fieldchar [0]) : 
                        fieldnum [0] += 1 
else : 
                        if fieldchar [0] : 
                            append_field () 
fieldchar [0] = char 
                        fieldnum [0] = 1 
else : 
                    if fieldchar [0] : 
                        append_field () 
charbuf.append (char) 
else : 
            if (quotebuf is not None) : 
            ...

    
    

    Fix the buggy line: if (type (append_chars) is DateTimePattern) :
assistant
#Here is Python program to fix the buggy line: if (type (append_chars) is DateTimePattern) :
.

if (type (pattern) is DateTimePattern) :