Two dimensional array in python

Solution 1:

You do not "declare" arrays or anything else in python. You simply assign to a (new) variable. If you want a multidimensional array, simply add a new array as an array element.

arr = []
arr.append([])
arr[0].append('aa1')
arr[0].append('aa2')

or

arr = []
arr.append(['aa1', 'aa2'])

Solution 2:

There aren't multidimensional arrays as such in Python, what you have is a list containing other lists.

>>> arr = [[]]
>>> len(arr)
1

What you have done is declare a list containing a single list. So arr[0] contains a list but arr[1] is not defined.

You can define a list containing two lists as follows:

arr = [[],[]]

Or to define a longer list you could use:

>>> arr = [[] for _ in range(5)]
>>> arr
[[], [], [], [], []]

What you shouldn't do is this:

arr = [[]] * 3

As this puts the same list in all three places in the container list:

>>> arr[0].append('test')
>>> arr
[['test'], ['test'], ['test']]

Solution 3:

What you're using here are not arrays, but lists (of lists).

If you want multidimensional arrays in Python, you can use Numpy arrays. You'd need to know the shape in advance.

For example:

 import numpy as np
 arr = np.empty((3, 2), dtype=object)
 arr[0, 1] = 'abc'

Solution 4:

You try to append to second element in array, but it does not exist. Create it.

arr = [[]]

arr[0].append("aa1")
arr[0].append("aa2")
arr.append([])
arr[1].append("bb1")
arr[1].append("bb2")
arr[1].append("bb3")

Solution 5:

We can create multidimensional array dynamically as follows,

Create 2 variables to read x and y from standard input:

 print("Enter the value of x: ")
 x=int(input())

 print("Enter the value of y: ")
 y=int(input())

Create an array of list with initial values filled with 0 or anything using the following code

z=[[0 for row in range(0,x)] for col in range(0,y)]

creates number of rows and columns for your array data.

Read data from standard input:

for i in range(x):
         for j in range(y):
             z[i][j]=input()

Display the Result:

for i in range(x):
         for j in range(y):
             print(z[i][j],end=' ')
         print("\n")

or use another way to display above dynamically created array is,

for row in z:
     print(row)