Difference between revisions of "Python-3.4.3/C2/Getting-started-with-strings/English"

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Evaluation  
 
Evaluation  
  
−
# Write code to assign the string ’ is called the apostrophe, to a variable s  
+
# Write code to assign the string ’ is called the apostrophe, to a variable s  
 
# How will you change s='hello' to s='Hello'.  
 
# How will you change s='hello' to s='Hello'.  
 
# The variables s and t are strings and r is integer.
 
# The variables s and t are strings and r is integer.
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| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| Here are some self assessment questions for you to solve  
 
| style="background-color:#ffffff;border:0.5pt solid #000001;padding-top:0cm;padding-bottom:0cm;padding-left:0.088cm;padding-right:0.191cm;"| Here are some self assessment questions for you to solve  
  
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# Write code to assign the given string to variable '''s'''
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# Write code to assign the string ’ is called the apostrophe, to a variable s  
 
# How will you change '''s''' ''is equal to '''hello' to '''s''' ''is equal to capital '''h Hello'.  
 
# How will you change '''s''' ''is equal to '''hello' to '''s''' ''is equal to capital '''h Hello'.  
 
# The variables '''s''' and '''t''' are strings and '''r''' is integer.
 
# The variables '''s''' and '''t''' are strings and '''r''' is integer.

Revision as of 15:24, 22 January 2018

'Python/C2/Getting Started with Strings/English'Title of script: Getting Started with Strings

Author: Trupti Kini


Visual Cue
Narration
Show Slide

containing title, name of the production team along with the logo of MHRD

Hello Friends. Welcome to the tutorial on "Getting Started with Strings".
Show Slide

Objectives

At the end of this tutorial, you will learn to,
  1. Define strings in different ways.
  2. Concatenate strings.
  3. Print a string repeatedly.
  4. Access individual elements of the string.
Show slide

System Specifications

To record this tutorial, I am using
  • Ubuntu Linux 16.04 operating system
  • Python 3.4.3 and
  • IPython 5.1.0
Show Slide

Pre-requisites

To practise this tutorial, you should know how to
  • run basic Python commands on the ipython console

If not, see the pre-requisite Python tutorials on this website.

Show Slide

What are Strings?

In Python, any character within a single/ double/ triple quotes is a string.

'This is a string'

“This is a string too”

‘’’This can be a large string’’’

What are strings?

In Python, any character within a single/ double/ triple quotes is a string.

For example:

Single, double, and triple quotes can be used to denote a string as shown here.

Show Slide

What are Strings?

Strings in triple quotes can be written in multiple lines.

We can also define empty strings.

String is a collection of characters which cannot be modified after it is created.

[Terminal]

ipython3

Let us first open the Terminal by pressing Ctrl+Alt+T keys simultaneously.

Type ipython3 and press Enter.

[IPython console]

%pylab and press Enter.

Let us initialise the pylab package.

Type %pylab and press Enter.

[IPython Terminal] Type

a = 'Hello, World!'

Let us clear the terminal.

We can assign a string to a variable called a.

Type a is equal to inside any quotes Hello comma World exclamation mark and

Press Enter

[IPython Terminal] Now let us learn string concatenation.

Let us assign strings to variables.

Type x = 'Hello'

y = 'World'

Type

x is equal to inside quotes Hello

Press Enter

y is equal to inside quotes World

Press Enter

Type z = x + ', ' + y + '!'

print(z)

Now, let us add the two strings.

z is equal to x plus inside quotes comma plus y plus inside quotes exclamation mark.

Press Enter

print inside parentheses z

Press Enter

Here x and y are string variables.

Highlight + The addition operation performs the concatenation of two strings.
Highlight Hello, World! Here we can see the output of string concatenation.
Type clear Let us clear the terminal.

What if we multiply a string with an integer?

Let us find out!

[IPython Terminal]

Press Up arrow till we get x

Type x * 5

Recall x string.

Press Enter

x multiplied by 5

Press Enter

Show Ipython Terminal

Highlight HelloHelloHelloHelloHello

The string Hello is repeated 5 times after multiplying.
Show Slide

Exercise 1

Pause the video. Try this exercise and then resume the video.

Obtain the string as shown without typing out all the twenty hyphens.

[IPython Terminal] Type,

s = "%% " + "-"*20 + "%%"

print(s)

Switch to the terminal for solution.

Type,

s is equal to inside quotes two percentages plus inside quotes hyphen multiplied by twenty plus inside quotes two percentages

Press Enter

print inside parentheses s

Press Enter

Let's now look at accessing individual elements of strings.

We can access individual elements in the string using the subscripts.

[IPython Terminal]

Press Up arrow till we get a

Type a[0]

Let us clear the terminal.

Recall a.

Press Enter.

Type,

a inside square brackets zero press Enter, gives us the first character of the string.

The indexing starts from 0 and goes up to (n-1).

where 'n' is the total number of characters in a string.

We can access the strings from the end using negative indices.

[IPython Terminal]

Type a[-1]

Type a[-2]

a inside square brackets minus one gives us the last element of the string i.e. exclamation mark

a inside square brackets minus two gives us the second element from the end of the string i.e. d

Show Slide

Exercise 2

s = “Hello World”

what is the output of

s[-5]

s[-10]

s[-15]

s[15]

Pause the video. Try this exercise and then resume the video.

Given a string, s which is Hello World, what is the output of the following


[Ipython Terminal]Type

s = "Hello World”

s[-5]

Switch to the terminal.

Let us clear the terminal.

Type

s is equal to inside quotes Hello World press Enter

s inside square brackets minus five gives W

Similarly we will get e for s[-10].

[Ipython Terminal]

Type s[-15]

s inside square brackets minus 15 gives us an IndexError.


Since the string given to us is only 11 characters long.

[Ipython Terminal]

Type s[15]

s inside square brackets 15 again gives IndexError for the same reason.
[Ipython Terminal]

Press Up arrow till we get x Type

x[0] = 'B'

Let us attempt to change one of the characters in a string.

Let us clear the terminal.

Recall x

Press Enter

Let us manipulate x.

x inside square brackets zero equal to inside quotes B press Enter

Highlight the error Why do we get an error?

Initially the value of x[0] is ‘H’.

Now we are trying to assign another value ‘B’ to x[0].

Recall, strings cannot be modified after it is created.

Show slide split() and join() functions We can split and join the strings by using the functions :

split() and join()

Show slide

Syntax for join()

str.join(sequence)

To join a string, the syntax is

str dot join inside parentheses sequence

[Ipython Terminal]

s = “-”

seq = ("a", "b", "c")

print (s.join( seq ))

Switch to the terminal.

Let us clear the terminal

Type

s is equal to inside quotes hyphen press Enter

seq is equal to inside parentheses a comma b comma c press Enter

print s dot join inside parentheses seq press Enter

Highlight a-b-c We will get output as a hyphen b hyphen c

It has joined a, b, c with hyphen.

Show slide syntax for split()

str.split()

To split a string, syntax is

str dot split open and close parentheses

[Ipython Terminal]

str = "Line1-abcdef \nLine2-abc \nLine4-abcd";print (str.split( ))

Switch to the terminal

Type as shown press Enter


print str dot split open and close parentheses press Enter

Highlight ['Line1-abcdef', 'Line2-abc', 'Line4-abcd'] We get the output like this.

It has split the strings at spaces.

Show Slide

Summary slide

This brings us to the end of this tutorial.

In this tutorial, we have learnt to,

  • Define strings in different ways.
  • Concatenate strings.
  • Print a string repeatedly and
  • Access individual elements of the string.
Show Slide

Evaluation

  1. Write code to assign the string ’ is called the apostrophe, to a variable s
  2. How will you change s='hello' to s='Hello'.
  3. The variables s and t are strings and r is integer.

s=”Hello”

t=”World”

r=2

What is the output of s * r + t * r?

Here are some self assessment questions for you to solve
  1. Write code to assign the string ’ is called the apostrophe, to a variable s
  2. How will you change s is equal to hello' to s is equal to capital h Hello'.
  3. The variables s and t are strings and r is integer.

They are assigned with the values as shown above, What is the output of s multiplied by r plus t multiplied by r?

Show Slide

Solutions

And the answers,
  1. The given string can be assigned in this manner
  2. Strings cannot be manipulated after it is assigned a value
  3. The operation s multiplied by r plus t multiplied by r will print each of the two words twice as HelloHelloWorldWorld
Show Slide

Forum

Please post your timed queries in this forum.
Show Slide

Fossee Forum

Please post your general queries on Python in this forum.
Show Slide

Textbook Companion

FOSSEE team coordinates the TBC project.
Show Slide

Acknowledgment

http://spoken-tutorial.org

Spoken Tutorial Project is funded by NMEICT, MHRD, Govt. of India.

For more details, visit this website.

Show Slide

Thank You

This is Trupti Kini from IIT Bombay signing off.

Thank you.

Contributors and Content Editors

Nancyvarkey, Nirmala Venkat, Trupti

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