def open_symbols_file(index):
	"""
	This function accept an index symbol as parameter, opens the corresponding file
	and returns a list  of the symbols.

	Parameters:
	----------
		index: str, the index symbol.
	Returns:
	-------
		symbols: list of symbols.
	"""

	f = open('data/symbols_files/' + index + '_symbols.dat', 'r')
	symbols = [symbol.strip() for symbol in f]

	f.close()

	return symbols