def skip_whitespace(s, start):
	"""Find the first non-whitespace character in a string.

	:param str s: an input string
	:param int start: an index where the search starts
	:return: index of the first non-whitespace character or len(s)"""
	i = start
	while i < len(s) and s[i].isspace():
		i += 1

	return i


def str_row_col(s, i):
	"""Translate a string index i to a row and col number.

	:param str s: an input string
	:param int i: an index pointing into s
	:return: a string position as (row, col)
	:rtype: (int, int)"""
	k = 0
	(r, c) = (0, 0)
	for (r, line) in enumerate(s.splitlines(True)):
		c = i-k
		if k+len(line) > i:
			break
		else:
			k += len(line)
	return (r+1, c+1)


class ParserError(Exception):
	def __init__(self, msg, s, i):
		self.msg = msg
		(self.row, self.col) = str_row_col(s, i)
		self.context = s[i:i+16]

	def __str__(self):
		return "{0} at row {1}, col {2}, got '{3}...' instead".format(self.msg, self.row, self.col, self.context)


class ParserWarning(ParserError):
	pass