what does "e.findIdx is not a function" mean in Minecraft MakeCode-Python?

Question

I have a very simple Python code in Minecraft MakeCode-Python, as below :

def My_fun(x, y, z, n, block_type):
    for i in range(n):
       blocks.fill(block_type[i],
            pos(x + i, y + i, z),
            pos(x + i, y + i, z),
            FillOperation.REPLACE)

block_type = [RED_WOOL,
    ORANGE_WOOL,
    YELLOW_WOOL,
    LIME_WOOL,
    CYAN_WOOL,
    BLUE_WOOL,
    PURPLE_WOOL]

My_fun(0, 0, 0, 7, block_type)

But it shows the following error message :

e.findIdx is not a function

The code is super simple but I have no idea about how to solve the problem, appreciate for your help !

Hi TheTridentGuy,Nigh-Anxiety,

"RED_WOOL" is a pre-defined object(?), if I hover mouse curser on it there is a message showing "RED_WOOD:Block.RED_WOOD". I actually don't know how to find more information about the "Block.RED_WOOD" in the MakeCode-Python environment.

Also, if I put "RED_WOOD" as the first input of the blocks.fill(), the code can be executed as expected, but if I put "block_type[i]" it throws error "e.findIdx is not a function". To my understanding "block_type" is a list and I should be able to access its element by the "[i]" indicator, though it seems not working here, any idea ? Thanks.