initializing a 2d array in python

Published May 9, 2023 Last updated May 9, 2023 Edit Source

• Py

I want to initialize an array like this: [[0,0],[0,0],...x]

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arr = [[]] * num

This way seem like it works, but the sub-array is only referenced. If you try to append to a sub array:

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arr = [[]] * 2
arr[0].push(1)

# -> [[1],[1]]

Every sub-array get’s appended to since they’re only references to one array.

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arr = [[] for i in range(num)]

This is the proper way to do it. Every sub-array is a it’s own instance.