Arrays

Array stores multiple values of the same type.

Types

A type must be defined when initializing array. This specifies what elements are contained (like integer, string and others).

The most common types and their codes are:

Type	Code
i	integer numbers (like 1, -5, 32)
I	positive integer numbers (like 8, 6, 7)
f	floating point numbers (like 3.5, 12.6, 8)
u	unicode symbols (like '*', 'g', '3')

The u type code for unicode characters is deprecated since version Python 3.3. Avoid using it.

Initialization

In order to initialize it the array module is used.

Empty array

Example of empty integer array:

import array as arr numbers = arr.array('i')

Initial values

In this example an array with 3 floating point numbers is created.

import array as arr numbers = arr.array('f', [7, 2.5, -8])

Type Mismatch

An exception is thrown if elements don't match the type code.

Let's analyze the following code:

import array as arr # 'i' allows only integer numbers (including positive and negative integers) int_numbers = arr.array('i', [-1, 3, 5]) # int_numbers = arr.array('i', [9, 3, 8.6]) # 'I' allows only positive integer numbers. positive_numbers = arr.array('I', [1, 3, 5]) positive_numbers.append(5) # positive_numbers.append(-9)

The only lines that throw exceptions are the commented lines (such as lines 5 and 10) due to the type mismatch.

Explanation:

• At Line 5 the i code allows only integer number but 8.6 does not match that.
• At Line 8 an array for positive numbers is declared.
• At Line 9 an element is added to the end of the array. Since 5 matches the type code (I - positive integers) it doesn't throw exception.
• At Line 10 an element is added - -9 which is not a positive integer. For that reason an exception would be thrown if the line is uncomented.

Similarities between array and list

Both data structure are used to store multiple values and share many similarities.

Some of them are:

• size - accessed via the len function. Example: len(numbers).
• value access - via indexes. Example: numbers[0].
• inserting element - via the append function. Example: numbers.append(5).
• index error - accessing element by index that's outside of the array bounds.

Basically list and array share the same functionalities and features.

Difference between array and list

Arrays can store values only of one type specified by the type code.

Lists can store values of different types. They are not bound to a single type.

Basically arrays are used only to guarantee that the stored values are from one type.

Let's analyze the following example:

import array as arr integer_array = arr.array('i', [-1, 3, 5]) # integer_array = arr.array('i', [-1, 3, 5, 'j']) list_example = [1, '**', 0.7, []]

• At line 3 an array of integers is created (specified by the code type i). All elements are from one single type - integers.
• Having values of different types (like in line 4) causes exception.
• Lists can store values of different types like in line 6.