在python中创建2D数组的两种方法

Question

What is the difference between the below two ways for creating 2d array in python?

def arrays(row, column):
    myList = [[None]*column for i in range(row)]

def arrays(row, column):
   myList = [[None]*column]*row

Answer 1

In the first case, separate pointers are used to store your sublists.

In the second instance, the same pointer is used. So changing the value of one will also change the others.

Here's an illustrative example:-

def arrays1(row, column):
    return [[None]*column for i in range(row)]

def arrays2(row, column):
    return [[None]*column]*row

x = arrays1(2, 2)
y = arrays2(2, 2)

x[0][0] = 1
y[0][0] = 1

print(x)  # [[1, None], [None, None]]
print(y)  # [[1, None], [1, None]]