'Read a giza-formatted string and return an Alignment object.
>>> Alignment.fromstring(\'0-0 2-1 9-2 21-3 10-4 7-5\')
Alignment([(0, 0), (2, 1), (7, 5), (9, 2), (10, 4), (21, 3)])
:type s: str
:param s: the positional alignments in giza format
:rtype: Alignment
:return: An Alignment object corresponding to the string representation ``s``.'

@classmethod
def fromstring(cls, s):

    return Alignment([_giza2pair(a) for a in s.split()])
