def _read_matrix(filename):
with open(filename) as f:
header = f.readline().split()
buf = list(map(lambda l: list(map(float, l[1:].split())), f.readlines()))
if len(buf) != len(header):
raise ValueError('Distance matrix must be square')
buf = list(zip(*buf))
for i, l in enumerate(buf):
if len(l) != len(header):
raise ValueError('Distance matrix must be square')
buf[i] = list(l[:i + 1:])
if not buf:
return None
res = TreeConstruction.DistanceMatrix(names=header,
matrix=buf)
return res
