Python3 Strings DS

Python Data Structures : Strings

Strings :

             A string is a sequence of characters.

  ***Computer do not deal with characters, they deal with numbers (binary) .Even though you may see characters on your screen, internally it is stored and manipulated as a combination of 0's and 1's.

       This conversion of character to a number is called encoding, and the reverse process is decoding. ASCII and Unicode are some of the popular encoding used.

  *   In python, string is a sequence of Unicode character.

How to create a string? 

    ->   Strings can be created by enclosing characters inside a single quote or double quotes.

    ->  Even triple quotes can be used in python but generally used to represent multiline strings and docstrings.

Eg:

       mystring='Hello'

       print(mystring)

 

       mystring="Hello"

       print(mystring)

       mystring=' ' 'Hello' ' '

       print(mystring)

output:  Hello

               Hello

               Hello

 How to access characters in a string?

Eg:    

       mystring="Hello"

  

       #print first character

       print(mystring[0])

       print(mystring[-1])

       print(mystring[2:5])

output: H

              o

              llo

  

  If we try to index out of range or use decimal number, we will get type error.

 

 How to change or delete a string ?

       Strings are immutable. This means that elements of a string cannot be changed once it has been assigned.

       We can simply reassign different strings to the same name.

       We cannot delete or remove character from a string. But deleting the string entirely is possible using the keyword del.

Eg:

       del mystring

       print(mystring)

output: ----------------------------------------------------------------

              --

              NameError

              NameError: name 'mystring' is not defined(because it is deleted)

String Operations :

Concatenation :

 

             Joining of two or more strings into a single one is called concatenation.

  The + operation does this in python. Simply writing two string literals together also concatenates them.

  The * operator can be used to repeat the string for a given number of times.

Eg:

       s1="Hello"

       s2="Sujith"

       print(s1+s2)       #concatenate 2 strings

       print(s1*3)         #repeat string n times

output:   Hello Sujith

                Hello Hello Hello

Iterating Through String :

Eg:

       count=0

       for l in "Hello World":

             if l=='o':

                  count+=1

       print(count, 'letters found')

output:  2 letters found

String Membership Test :

  

       print('l' in 'Hello world')

output:  True

 

       print('or' in 'Hello world')

output:  True

String Methods :

             Some of the commonly used methods are lower( ), upper( ), join( ), split( ), find( ), replace( ) etc.

Eg:

       "Hello".lower( )

    

output:  'hello'

       "Hello".upper( )

output:  'HELLO'

       "This will split all words in a list".split( )

output: ['This','will','split','all','words','in','a','list']

       ' '.join(['This', 'will', 'split', 'all', 'words', 'in', 'a', 'list'])

output:  'This will split all words in a list'

       "Good Morning".find("Mo")

output:  5

       "Bad Morning".replace("Bad","good")

output:  'Good Morning'

Python Program to Check where a String is Palindrome or not ?

       mystr="MadaM"

       myStr=mystr.lower( )

       revstr=reversed(myStr)

       if list(myStr)==list(revstr):

           print("Given string is palindrome")

       else:

           print("Given string is not palindrome")

output:  Given string is palindrome

Python Program to Sort Words in Alphabetic Order ?

 

       mystr="python program to sort words in alphabetic order"

       words=mystr.split( )

       words.sort( )

       for word in words:

            print(word)

output:  alphabetic

               order

               program

               sort

               in

               python

               to

               words