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Python – Initialize empty array of given length

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  • Difficulty Level : Basic
  • Last Updated : 06 Dec, 2019

Prerequisite: List in Python

As we know Array is a collection of items stored at contiguous memory locations. In Python, List (Dynamic Array) can be treated as Array. In this article, we will learn how to initialize an empty array of some given size.

Let’s see different Pythonic ways to do this task.

Method 1 –

Syntax:

list1 = [0] * size
list2 = [None] * size




# initializes all the 10 spaces with 0’s
a = [0] * 10 
  
# initializes all the 10 spaces with None
b = [None] * 10 
  
# initializes all the 10 spaces with A's
c = ['A'] * 5 
  
# empty list which is not null, it's just empty.
d = [] 
  
print (a, "\n", b, "\n", c, "\n", d);

Output:

[0, 0, 0, 0, 0, 0, 0, 0, 0, 0] 
[None, None, None, None, None, None, None, None, None, None] 
['A', 'A', 'A', 'A', 'A'] 
[]

 
Method 2 – Use loops just like C and assign the size.

Syntax:

a = [0 for x in range(size)] #using loops




a = []
b = []
  
# initialize the spaces with 0’s with 
# the help of list comprehensions
a = [0 for x in range(10)]
print(a)
  
# initialize multi-array 
b = [ [ None for y in range( 2 ) ]
             for x in range( 2 ) ]
               
print(b)

Output:

[0, 0, 0, 0, 0, 0, 0, 0, 0, 0]

[[None, None], [None, None]]

 
Method 3 – Using Numpy to create empty array.




import numpy
  
# create a simple array with numpy empty()
a = numpy.empty(5, dtype=object)
print(a)
  
# create multi-dim array by providing shape
matrix = numpy.empty(shape=(2,5),dtype='object')
print(matrix)

Output:

[None None None None None]

[[None None None None None]
 [None None None None None]]

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