CODEWITHSUNDEEP
python-3.xmatrixinitialization
user2804578
user2804578

Reputation: 32

Initializing matrix python3

I don't know whether this is a bug, or I got a wrong semantic meaning of the * token in arrays:

>>> arr = [None] * 5    # Initialize array of 5 'None' items
>>> arr
[None, None, None, None, None]
>>> arr[2] = "banana"
>>> arr
[None, None, 'banana', None, None]
>>> # right?
... 
>>> mx = [ [None] * 3 ] * 2     # initialize a 3x2 matrix with 'None' items
>>> mx
[[None, None, None], [None, None, None]]
>>> # so far, so good, but then:
... 
>>> mx[0][0] = "banana"
>>> mx
[['banana', None, None], ['banana', None, None]]
>>> # Huh?

Is this a bug, or did I got the wrong semantic meaning of the __mult__ token?

Upvotes: 0

Views: 1576

Answers (1)

Ben
Ben

Reputation: 421

You're copying the same reference to the list multiple times. Do it like this:

matrix = [[None]*3 for i in range(2)]

Upvotes: 1

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