def parseSingleLink(line):
	"""Parse a single link having the format: src dst [weight]

	line  - non-empty line of the input text that starts from a non-space symbol

	return  [src_str, dst_str, weight_str | None],
	"""
	line = line.split(None, 3)  # Ending comments are not allowed, but required unweighted link might contain input weight
	assert len(line) >= 2 and  line[0][0].isdigit() and line[1][0].isdigit(), (
		'src and dst must exist and be digits')
	if len(line) == 2:
		line.append(None)
	else:
		assert line[2][0].isdigit() or line[2][0] == '.', 'Weight should be a float number'

	return line