Python Tutorial - Data Type-Array

1. Python Array Declaration
2. Python Array Index
3. Array Negative Index
4. Traverse Through a Python Array
5. Python Array Update
6. Different Ways to Modify a Python Array
7. Delete Elements From a Python Array
8. Array Methods

In this section, you will learn how to create and access elements of arrays in Python.

An array is a collection of elements of the same data type. The main difference between an array and a list is that a list can have elements of different data types.

In Python programming, to create an array, you need to import array module because an array is not a fundamental data type.

from array import *

Python Array Declaration

To declare an array you have to follow the syntax below:

arrayName = array(typecode, [initializers])

Here, arrayName is the name of the array, typecode determines the data type of the array and initializers are the values in the array.

You will learn more about typecode parameter later in this section.

Consider the example below:

a = array("i", [1, 2, 3, 4])

The name of the array is a, typecode is i which specifies that values of the array will be of integer data type. If you try to store values other than the integers in this array, an error will be raised:

>>> a=array('i', [1,2,3.4,4])
Traceback (most recent call last):
  File "<pyshell#4>", line 1, in <module>
    a=array('i', [1,2,3.4,4])
TypeError: integer argument expected, got float

Let’s check the example of an array that contains some integers:

>>> from array import *
>>> a = array('i', [1,2,3,4])
>>> for i in a:
	print(i)
1
2
3
4

typecode Parameter

Python Array Index

You can fetch an element of an array using the index operator [].

Retrieve an Element of the Array Using Index Operator

>>> a = array('i', [1,2,3,4])
>>> print("First element of array =", a[0])
First element of array = 1
>>> print("Second element of array =", a[1])
Second element of array = 2

Get the Index of Given Value by Using Index(x) Method

The index(x) method returns the smallest index of the first occurrence of x.

>>> a = array('i', [1,2,3,4])
>>> print("1 is found at location:", a.index(1))
1 is found at location: 0
>>> print("4 is found at location:", a.index(4))
4 is found at location: 3

Array Negative Index

Similar to other Python sequential data types like strings, lists, tuples, range objects, you could also use negative indexes to access elements in the array.

>>> a = array('i', [1,2,3,4])
>>> print("last element of array:",a[-1])
last element of array: 4

Traverse Through a Python Array

First thing first, finding the length of the array:

Array Len() Method

The len() method returns the number of elements in an array.

>>> a = array('i', [1,2,3,4])
>>> print("length of a:", len(a))
length of a: 4

Iterate Over an Array

You can use for loop to iterate through elements of an array.

>>> a = array('i', [1,2,3,4])
>>> for i in range(len(a)):
	print(a[i])
1
2
3
4

or

>>> a = array('i', [1,2,3,4])
>>> for i in a:
	print(i)
1
2
3
4

Python Array Update

Append()

You can use the array method append() to append an item to the end of an array.

>>> a = array('i', [1,2,3,4,5,7,8,9])
>>> a.append(10)
>>> print(a)
array('i', [1, 2, 3, 4, 5, 7, 8, 9, 10])

Insert(i, X)

You could use insert(i, x) method to insert the element x to the given index i.

>>> a = array('i', [1,2,3,4,5,7,8,9])
>>> a.insert(3,44)
>>> print(a)
array('i', [1, 2, 3, 44, 4, 5, 7, 8, 9])

Extend(x)

append(x) adds the item x as one item to the array. extend(x) method is the right method to extend the array by appending all the elements in the given object x.

>>> a = array('i', [1,2,3,4,5,7,8,9])
>>> a.extend([10,11,12,13,14,15])
>>> print(a)
array('i', [1, 2, 3, 4, 5, 7, 8, 9, 10, 11, 12, 13, 14, 15])

Fromlist()

fromlist() adds items from a list into the array.

>>> a = array('i', [1,2,3,4,5,7,8,9])
>>> l = [10,11]
>>> a.fromlist(l)
>>> print(a)
array('i', [1, 2, 3, 4, 5, 7, 8, 9, 10, 11])

Different Ways to Modify a Python Array

Reverse()

reverse() reverses the array.

>>> a = array('i', [1,2,3,4,5,7,8,9])
>>> a.reverse()
>>> print(a)
array('i', [9, 8, 7, 5, 4, 3, 2, 1])

+ Operator

Two arrays can be concatenated by using + operator:

>>> a = array('i', [1,2,3,4,5,7,8,9])
>>> b = array('i', [10,11])
>>> print(a + b)
array('i', [1, 2, 3, 4, 5, 7, 8, 9, 10, 11])

* Operator

* operator repeats elements in the array a specific number of times.

>>> a = array('i', [1,2,3,4,5,7,8,9])
>>> a = a * 2
>>> print(a)
array('i', [1, 2, 3, 4, 5, 7, 8, 9, 1, 2, 3, 4, 5, 7, 8, 9])

Here the elements are repeated twice.

Delete Elements From a Python Array

The del statement deletes one or more items from an array. You can also use del to delete the entire array:

>>> a = array('i', [1,2,3,4,5,7,8,9])
>>> del a[3]
>>> print(a)
array('i', [1, 2, 3, 5, 7, 8, 9])
>>> del a			#entire array is deleted

Remove(x)

remove() removes the first occurrence of x from an array:

>>> a = array('i', [1,2,3,4,5,7,8,9,3])
>>> a.remove(3)
>>> print(a)
array('i', [1, 2, 4, 5, 7, 8, 9, 3])

Pop()

pop() will remove and return the last element from the array.

>>> a = array('i', [1,2,3,4,5,7,8,9])
>>> a.pop()
9
>>> print(a)
array('i', [1, 2, 3, 4, 5, 7, 8])

Array Methods

The following table describes the array methods,: