# Find letter index from all_letters, e.g. "a" = 0
def letterToIndex(letter):
    # return our out-of-vocabulary character if we encounter a letter unknown to our model
    if letter not in allowed_characters:
        return allowed_characters.find("_")
    else:
        return allowed_characters.find(letter)

# Turn a line into a <line_length x 1 x n_letters>,
# or an array of one-hot letter vectors
def lineToTensor(line):
    tensor = [torch.zeros](https://docs.pytorch.org/docs/stable/generated/torch.zeros.html#torch.zeros "torch.zeros")(len(line), 1, n_letters)
    for li, letter in enumerate(line):
        tensor[li][0][letterToIndex(letter)] = 1
    return tensor