Python-Strings(review)

Lets start the topic for the day.- "Strings in Python"

Google Meet Link for today's class is:

Meeting ID

meet.google.com/pgq-dhdf-gnn

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By the end of the session, you will be able to 

• Understand the string data type
• definition and purpose of string data type
• Ways to print strings
• Apply the concatenation operator ,repetition operators, slicing ,accessing the specific characters in a string  and  predict the output.

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Python Strings

• Strings in Python are identified as a contiguous set of characters represented in the quotation marks. 
• Python allows for either pairs of single or double quotes. 
• Example:

              "Geeta",         'Pratham',      "1234",        '786'

• Two types of strings supported in Python
• Single Line String


• Strings that are terminated in within a single line.

                            

                        Output will be:

         

• Multiline string
• Piece of text that is spread along multiple lines
• two ways to create Multiline Strings:
• Adding back slash at the end of each line.

The Output will be:



• Using Triple quotation marks:
• To create Multiline strings, we use three pairs of single/double quotes.

                                         

The Output will be :
                                          

Python Strings

• Strings in Python are identified as a contiguous set of characters represented in the quotation marks. 
• Python allows for either pairs of single or double quotes. 
• Subsets of strings can be taken using the slice operator ([ ] and [:] ) with indexes starting at 0 in the beginning of the string and working their way from -1 at the end.
• The plus (+) sign is the string concatenation operator.
•  The asterisk (*) is the repetition operator. For example −

(To check the output,Click on "Live Demo" )

Live Demo

#!/usr/bin/python

str = 'Hello World!'

print str          # Prints complete string
print str[0]       # Prints first character of the string
print str[2:5]     # Prints characters starting from 3rd to 5th
print str[2:]      # Prints string starting from 3rd character
print str * 2      # Prints string two times
print str + "TEST" # Prints concatenated string

This will produce the following result −

Hello World!
H
llo
llo World!
Hello World!Hello World!
Hello World!TEST

EXERCISE

What can you say about the string data type?
Is there a difference between "Geeta" and 'Geeta'? Justify.
Predict the output of the following:

print("SCS"*5)
print(("SCS"," ")*5)
print("I"+"Love"+"Columbas")
print("I","Love","Columbas")
print("I\n"+"Love\n"+"Columbas\n")
print("I\t"+"Love\t"+"Columbas\t")

Suppose 

           str='I LOVE COLUMBAS'

Predict the output of the following:

print str          # Prints complete string
print str[0]       # Prints first character of the string
print str[2:5]     # Prints characters starting from 3rd to 5th
print str[2:14]    # Prints string starting from 3rd character
print str * 2      # Prints string two times 

print str[0:5] + " MUSIC"

Strings are amongst the most popular types in Python. We can create them simply by enclosing characters in quotes. Python treats single quotes the same as double quotes. Creating strings is as simple as assigning a value to a variable. For example −

var1 = 'Hello World!'
var2 = "Python Programming"

Accessing Values in Strings

Python does not support a character type; these are treated as strings of length one, thus also considered a substring.

To access substrings, use the square brackets for slicing along with the index or indices to obtain your substring. For example −

Live Demo

#!/usr/bin/python

var1 = 'Hello World!'
var2 = "Python Programming"

print "var1[0]: ", var1[0]
print "var2[1:5]: ", var2[1:5]

When the above code is executed, it produces the following result −

var1[0]:  H
var2[1:5]:  ytho

Updating Strings

You can "update" an existing string by (re)assigning a variable to another string. The new value can be related to its previous value or to a completely different string altogether. For example −

Live Demo

#!/usr/bin/python

var1 = 'Hello World!'
print "Updated String :- ", var1[:6] + 'Python'

When the above code is executed, it produces the following result −

Updated String :-  Hello Python

Escape Characters

Following table is a list of escape or non-printable characters that can be represented with backslash notation.

An escape character gets interpreted; in a single quoted as well as double quoted strings.

Backslash notation		Description
\a		Bell or alert
\b		Backspace
\cx		Control-x
\C-x		Control-x
\e		Escape
\f		Formfeed
\n		Newline
\r		Carriage return
\s		Space
\t		Tab
\v		Vertical tab

String Special Operators

Assume string variable a holds 'Hello' and variable b holds 'Python', then −

Operator	Description	Example
+	Concatenation - Adds values on either side of the operator	a + b will give HelloPython
*	Repetition - Creates new strings, concatenating multiple copies of the same string	a*2 will give -HelloHello
[]	Slice - Gives the character from the given index	a[1] will give e
[ : ]	Range Slice - Gives the characters from the given range	a[1:4] will give ell
in	Membership - Returns true if a character exists in the given string	H in a will give 1
not in	Membership - Returns true if a character does not exist in the given string	M not in a will give 1