How to unpack this generator

Question

I have written code for the zig-zag problem on LeetCode. The function works correctly when I use a multi-line for loop. However the current print statement outputs a generator function. I tried using the * key but it didn't seem to work.

How do I unpack this generator function?

The output I want is a string, not a list.

Thanks

def zigzag (word, num_rows):
    array = [] 
    for _ in range(num_rows):
        array.append([])
    increasing = 1
    array_index = 0
    word_index = 0

    while word_index < len(word):
        if increasing: 
            array[array_index].append(word[word_index])
            array_index +=1 
            word_index +=1
        else:
            array[array_index].append(word[word_index])
            array_index -=1 
            word_index +=1 
        if array_index == -1 and increasing == 0: 
            increasing = 1
            array_index = 1
        if array_index == num_rows and increasing == 1:
            increasing = 0
            array_index = num_rows - 2 
    return array



if __name__ == "__main__":
    word = "PAYPALISHIRING"
    num_rows = 4
    print ("".join(line) for line in zigzag(word, num_rows))

Answer 1

One line for-loop:

print ("".join(line for array in zigzag(word, num_rows) for line in array))

# PINALSIGYAHRPI