How to declare an array in Python

In this article, you will learn about arrays and how to declare arrays in Python. You will see some simple code examples to understand how you can create an array in Python.

In Python, array declaration cannot be done directly, because Python doesn't have any support for Array type bt default.

Note: Array does not exist as a built-in data structure in Python. Python uses list type instead of the array.

What is Array?

• An array is like a storage container where multiple items of the same type are stored.

• Like other data structures, arrays can also be accessed using indexes.

• Elements stored in an array have a location as a numerical index.

• The Index starts from 0 and ends with the length of the array-1.

• Arrays use contiguous memory locations to store data.

• Arrays look similar to the Python Lists but have different properties and different declarations.

Let us look at the different ways to declare arrays in Python. We will use simple approaches, an array module supported by Python, NumPy module, use a list to create an array, and also a direct method to initialize an array.

1. Declare Array in Python using List

As mentioned earlier, there is no built-in support for arrays in Python, but we can use Python lists to create array-like structures,

array1 = [0, 0, 0, 1, 2]
array2 = ["cap", "bat", "rat"]

1.1. Example: Creating array just like Python list

Here, we declare an empty array. Python for loop and range() function is used to initialize an array with default values.

• You might get confused between lists and arrays but lists are nothing but dynamic arrays.

• Also, arrays store similar types of data whereas in lists you can store different types of data.

The below code example has an empty array. It is initialized with 5 elements carrying a default value (0).

arr = []
arr = [0 for i in range(5)] 
print(arr)

[0, 0, 0, 0, 0]

2. Declare an Array using the array module

Array does not exist as a built-in data structure in Python. However, Python provides a array module to declare a set of data that acts as as an array.

Here is the syntax for using it:

arrayName = array(typecode, [Initializers])

2.1. Parameters taken by array() method:

In the above syntax, typecode is used to set the codes that are used to define the type of value the array will hold.

As you can see in the table above, you can use the type code 'i' for using integer type values in the array, or 'f' for float type values, etc.

Initializers - a set of values of similar types, like, [1, 2, 3] or ["abc", "pqr", "xyz"], etc.

2.2. Creating Array using array Module

The below code example imports the Python array module and uses it to create an array in Python.

It declares an array of a set of signed integers and then prints the elements.

from array import *

array1 = array('i', [10,20,30,40,50])

for x in array1:
    print(x)

10
20
30
40
50

Next, lets see how we can use the Numpy package to create and declare array in Python.

3. Python NumPy module to create an array

Python has a module numpy that can be used to declare an array.

It creates arrays and manipulates the data in them efficiently.

The numpy.empty() function is used to create an array. Let's see a code example,

import numpy as np

arr = np.empty(10, dtype=object)
print(arr)

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

4. Create an Array using an initializer

This method creates an array with the default values along with the specified size inside the initializer.

See the code example below:

arr_num = [0] * 2
print(arr_num)

arr_str = ['P'] * 5
print(arr_str)

[0, 0]
['P', 'P', 'P', 'P', 'P']

FAQs

Here are some frequently asked questions related to Python array declaration.

Q. Are arrays supported in Python?

Arrays are not supported in Python by default. But we can create array-like structures using Python lists.

Q. How do you declare and initialize an array in Python?

There are many different ways in which you can declare and initialize an array in Python. For example, you can use a for loop and create a list of items that can act as an array for you. Here is the code example,

# empty array
arr = []
# array with some values
arr = [0 for i in range(5)] 
print(arr)

Q. How do you initialize an array size in Python?

Because arrays are not supported in Python by default, so there is no direct way to initialize an array size in Python. But you can create a simple array using a Python list and add some values to it to initialize the array size.

For example,

arr1 = [0, 0, 0, 1, 2]
arr2 = ["cap", "bat", "rat"]

In the code example above, both arr1 and arr2 have size 3.

Q. How to fill array in Python?

There are many ways to create an array in Python and fill an array with values in Python. You can use the literal style using a Python list, or use a for loop to set values, of use the array module in Python to create an array and fill values in the array in Python.

Here are some code examples,

# fill values using for loop
arr1 = [0 for i in range(5)]

# fill values using literal style
arr2 = [1, 2, 3, 4, 5] 

# using initializer
arr3 = [0] * 2

Go on try these and you will see that all the variables have values filled in them.