variable out of scope but still works-CodePudding

I am following the pytorch tutorial here and got to the word embeddings tutorial but there is some code I do not understand.

When constructing n-grams they use the following:

ngrams = [
    (
        [test_sentence[i - j - 1] for j in range(CONTEXT_SIZE)],
        test_sentence[i]
    )
    for i in range(CONTEXT_SIZE, len(test_sentence))
]

This to me does not seem syntactically correct as i is referenced before it is initialized, there is nothing inside the for loop, and the for loop is missing the : at the end. What is going on with this block of code? It does not seem like it should work but it does.

CodePudding user response：

This is a syntax of python like you can define a list like this:

a_list = [i*2 for i in range(100)]

in your example it is defining a 2-D list, so there are two for loop like:

b_list = [(a_list) for j in range(2)]

if we combine, we can write them like the example you posted.