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I'm attempting to make a Tetris clone in python, and want to make my code more efficient. I want a variable named board to be a 20 * 10 array with False in each cell, a 2 by 2 example of this being

board = [[False, False], [False, False]]

When it comes to making a 20 by 10 array of all the same variable, the code gets a bit cumbersome. This is what I've tried to construct the grid:

board = [[False * 10] * 22]

However, it returns [[0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]].

I understand why it returns this, but how can I make it return the wanted array?

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1 Answer 1

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5

In your example, you are multiplying False by 10 (0*10), and repeating it 22 times. Hence the result

Try this:

board = [[[False] * 10] * 22] #Cast the boolean to a list

DEMO

>>> [[False] * 10] * 22
[[False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False]]

As Ashwini mentioned in the comment, this creates references of the same object in the inner list.

Example:

>>> x[0][0] = True
>>> x
[[True, False, False, False, False, False, False, False, False, False], [True, False, False, False, False, False, False, False, False, False], [True, False, False, False, False, False, False, False, False, False], [True, False, False, False, False, False, False, False, False, False], [True, False, False, False, False, False, False, False, False, False], [True, False, False, False, False, False, False, False, False, False], [True, False, False, False, False, False, False, False, False, False], [True, False, False, False, False, False, False, False, False, False], [True, False, False, False, False, False, False, False, False, False], [True, False, False, False, False, False, False, False, False, False], [True, False, False, False, False, False, False, False, False, False], [True, False, False, False, False, False, False, False, False, False], [True, False, False, False, False, False, False, False, False, False], [True, False, False, False, False, False, False, False, False, False], [True, False, False, False, False, False, False, False, False, False], [True, False, False, False, False, False, False, False, False, False], [True, False, False, False, False, False, False, False, False, False], [True, False, False, False, False, False, False, False, False, False], [True, False, False, False, False, False, False, False, False, False], [True, False, False, False, False, False, False, False, False, False], [True, False, False, False, False, False, False, False, False, False], [True, False, False, False, False, False, False, False, False, False]]
>>>

A work around would be to use: 

[[False for _ in range(10)] for _ in range(22)]

DEMO

>>> y = [[False for _ in range(10)] for _ in range(22)]
>>> y
[[False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False]]
>>> y[0][0] = True
>>> y
[[True, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False], [False, False, False, False, False, False, False, False, False, False]]
>>>
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1 Comment

Also creating list this way is still a bad idea, all the inner lists point to same object.

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