'See `FITSDiff` for explanations of the initialization parameters.'

def __init__(self, a, b, ignore_keywords=[], ignore_comments=[], rtol=0.0, atol=0.0, ignore_blanks=True, ignore_blank_cards=True, tolerance=None):

    self.ignore_keywords = set((k.upper() for k in ignore_keywords))
    self.ignore_comments = set((k.upper() for k in ignore_comments))
    self.rtol = rtol
    self.atol = atol
    if (tolerance is not None):
        warnings.warn('"tolerance"    was    deprecated    in    version    2.0    and    will    be    removed    in    a    future    version.    Use    argument    "rtol"    instead.', AstropyDeprecationWarning)
        self.rtol = tolerance
    self.ignore_blanks = ignore_blanks
    self.ignore_blank_cards = ignore_blank_cards
    self.ignore_keyword_patterns = set()
    self.ignore_comment_patterns = set()
    for keyword in list(self.ignore_keywords):
        keyword = keyword.upper()
        if ((keyword != '*') and glob.has_magic(keyword)):
            self.ignore_keywords.remove(keyword)
            self.ignore_keyword_patterns.add(keyword)
    for keyword in list(self.ignore_comments):
        keyword = keyword.upper()
        if ((keyword != '*') and glob.has_magic(keyword)):
            self.ignore_comments.remove(keyword)
            self.ignore_comment_patterns.add(keyword)
    self.common_keywords = []
    self.diff_keyword_count = ()
    self.diff_keyword_positions = ()
    self.diff_keywords = ()
    self.diff_duplicate_keywords = {}
    self.diff_keyword_values = defaultdict(list)
    self.diff_keyword_comments = defaultdict(list)
    if isinstance(a, string_types):
        a = Header.fromstring(a)
    if isinstance(b, string_types):
        b = Header.fromstring(b)
    if (not (isinstance(a, Header) and isinstance(b, Header))):
        raise TypeError('HeaderDiff    can    only    diff    astropy.io.fits.Header    objects    or    strings    containing    FITS    headers.')
    super(HeaderDiff, self).__init__(a, b)
