LETTERS = ['A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V',
		   'W', 'X', 'Y', 'Z']


def is_letter_of_alphabet(letter: str):
	"""
	Checks if the given letter is a valid letter of the alphabet
	:param letter: The letter to check
	:return: If the letter is in the alphabet
	"""
	return letter.upper() in LETTERS


def get_letter_at_index(idx: int, capital: bool = False):
	"""
	Returns the letter at the given index
	:param idx: The index of the letter to return
	:param capital: If the capitalized letter should be returned
	:return: The letter
	"""
	if idx < 0 or idx > 25:
		raise AttributeError

	return LETTERS[idx] if capital else LETTERS[idx].lower()


def get_index_of_letter(letter: str):
	"""
	Returns the index of the given letter
	:param letter: The letter to return the index of
	:return: The index of the letter
	"""
	if letter.upper() not in LETTERS:
		raise AttributeError

	return LETTERS.index(letter.upper())