List.extend() is not working as expected in Python

Question

I have a list queueand an iterator object neighbors whose elements I want to append to the list.

queue = [1]
neighbor = T.neighbors(1) #neighbor is a <dict_keyiterator at 0x16843d03368>
print(list(neighbor)) #Output: [2, 3]
queue.extend([n for n in neighbor])
print(queue)

Output:

[1]

Expected Output:

[1, 2, 3]

What is going wrong?

Asked By: Kshitiz

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Source

Answer 1

You consumed the iterator already:

print(list(neighbor))

Take that line out.

Answered By: user2357112

Answer 2

You already exhaust the iterator neighbor when you use it in the list constructor for printing, so it becomes empty in the list comprehension in the next line.

Store the converted list in a variable so you can both print it and use it in the list comprehension:

queue = [1]
neighbor = T.neighbors(1) #neighbor is a <dict_keyiterator at 0x16843d03368>
neighbors = list(neighbor)
print(neighbors) #Output: [2, 3]
queue.extend([n for n in neighbors])
print(queue)

Answered By: blhsing

List.extend() is not working as expected in Python

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