Python array

What Is Array?
• An array is an mutable object which store a collection of values of
same data type under a single reference.
• An array store only homogeneous data type.
• Python's array is dynamic array.
• In Python we need declaration of array before use it in program.
• 'array' module must be imported for handling array in Python.

Advantages Of Array
I. Performance: For huge number of elements array take less memory
spaces and execution time also faster if compare with list.
II. Dynamic: Array's size is not fixed, so we can increase or decrease its
size at run time.
III. array module: Python provide 'array' module which contain
different methods, classes, objects to process array very easily.

Array vs. List
Topic Array List
Type of data structure
It is not built - in. We need
import 'array' module
before using array.
It is built - in. There are no
need to import any extra
module or package.
Necessity of declaration
Requires specific function
to declare an array.
No requirement of specific
function to declare a list.
Data type
Support only
homogeneous type.
Always support different
types of data in a list.

Array vs. List
Topic Array List
Handling large data
Store data very compact
way, so array more
efficient to handle large
data.
It is not so much efficient
to handle large data.
Numerical operations
Arryas are efficient for
various types of numerical
operations.
Lists can not handle
numerical operations
directly.

'array' Module
• If you working with array you need to import 'array' module.
• According to Python documentation “This module defines an object
type which can compactly represent an array of basic values:
characters, integers, floating point numbers.”
• Import array module as following way:
>>> import array

Declaring Array
• The syntax of array declaration is:
• 'array_name' is an identifier, which store reference of array object.
• 'array.array( )' first array represent 'array' module and second array
represent array class which resides in 'array' module.
• 'type_code' represent the data type of array's elements.
• '[ elements ]' represent list of values which we want to store in array.
array_name = array.array( type_code, [ elements ] )

List Of 'type_code'
type_code Data type Minimum size in
bytes
'b' Signed integer 1
'B' Unsigned integer 1
'i' Signed integer 2
'I' Unsigned integer 2
'l' Signed integer 4
'L' Unsigned integer 4

List Of 'type_code'
type_code Data type Minimum size in
bytes
'f' Floating point 4
'd' Double precision
floating point
8
'u' Unicode character 2

Array Declaration Example
>>> import array
>>> my_array = array.array( 'i', [ 5, 7, 11, 14 ] )
>>> for i in my_array:
print( i )
5
7
11
14

Programming Example
• A program to create an array to store the characters of word
'Welcome' and display all characters.
>>> import array
>>> my_array = array.array( 'u', [ 'W', 'e', 'l', 'c', 'o', 'm', 'e' ] )
>>> for i in my_array:
print( i )
W m
e e
l
c
o

Different Ways Of Importing Array Module
• Import array module with an alias or alternate name as below:
• Here 'arr' is an alias name of imported module.
• For example:
>>> import array as arr
>>> my_array = arr.array( 'i', [ 5, 7, 11, 14 ] )
>>> import array as arr

Different Ways Of Importing Array Module
• Second way of importing 'array' module is below:
• Here '*' means all. That means we import all things such as classes,
objects, variables etc. of array module in our program.
• For example:
>>> from array import *
>>> my_array = array( 'i', [ 5, 7, 11, 14 ] )

Indexing On Arrays
• An index represent position value of an element in an array.
• Array index always start from 0.
• For example:
>>> x = array( 'i', [ 5, 7, 11, 14 ] )
>>> print( x[ 2 ] )
11
5 7 11 14
x[ 0 ] x[ 1 ] x[ 2 ] x[ 3 ]

Accessing Array Using Index
- By for loop
from array import *
a = array( 'i', [ 34, 56,-12, 44 ] )
n = len( a )
for i in range( n ):
print( a[ i ], 't', end = ' ' )
34 56 -12 44

Accessing Array Using Index
- By while loop
from array import *
a = array( 'i', [ 34, 56,-12, 44 ] )
n = len( a )
i = 0
while i < n:
print( a[ i ], 't', end = ' ' )
i += 1
34 56 -12 44

Slicing On Array
• By slicing operation we can retrive a piece of array out of an array.
• The syntax of slicing is:
• For example:
array_name[ start: stop: stride ]
>>> x = array( 'i', [ 10, 20, 30, 40, 50, 60, 70, 80, 90 ] )
>>> print( x[ 1: 4 ] )
array('i', [20, 30, 40])
>>> print( x[ 1: : 2 ] )
array('i', [20, 40, 60, 80])

Slicing On Array
array('i', [20, 40, 60, 80])
>>> print( x[ : 8: 2 ] )
array('i', [10, 30, 50, 70])
>>> print( x[ -1: : ] )
array('i', [90])
>>> print( x[ : : -1 ] )
array('i', [90, 80, 70, 60, 50, 40, 30, 20, 10])
>>> print( x[ : -5: -1 ] )
array('i', [90, 80, 70, 60])
>>> print( x[ -5: : ] )
array('i', [50, 60, 70, 80, 90])

Programming Example
• A program to calculate sum of a range of elements in an array.
from array import *
x = array( 'i', [ 10, 20, 30, 40, 50, 60, 70, 80, 90 ] )
sum = 0
for i in x[ 2: 5 ]:
sum = sum + i
print( sum )

Python array

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