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

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

Objectives

1. Define strings in different ways.
2. Concatenate strings.
3. Print a string repeatedly.
4. Access individual elements of the string.

System Specifications

• Ubuntu Linux 16.04 operating system
• Python 3.4.3
• IPython 5.1.0

Pre-requisites

• run basic Python commands on the ipython console

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

What are Strings?

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

Example:

'This is a string'

“This is a string too”

‘’’This can be a large string’’’

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.

What are Strings?

We can also define empty strings.

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

ipython3

Type ipython3 and press Enter.

%pylab and press Enter.

Type %pylab and press Enter.

a = 'Hello, World!'

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

Let us assign strings to variables.

y = 'World'

x is equal to inside quotes Hello

Press Enter

y is equal to inside quotes World

Press Enter

print(z)

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.

What if we multiply a string with an integer?

Let us find out!

Press Up arrow till we get x

x * 5

Press Enter

x multiplied by 5

Press Enter

Highlight the output

Exercise 1

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

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

print(s)

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

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

Press Up arrow till we get a

a[0]

Recall a.

Press Enter.

Type,

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

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

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

a[-1]

a[-2]

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

Exercise 2

s = “Hello World”

what is the output of

s[-5]

s[-10]

s[-15]

s[15]

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

s[-5]

s[-10]

s[-15]

s[15]

s = "Hello World”

s[-5]

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].

s[-15]

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

s[15]

Press Up arrow till we get x

x[0] = 'B'

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

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.

split() and join()

Syntax for join()

str.join(sequence)

str dot join inside parentheses sequence

s = “-” seq = ("a", "b", "c") print (s.join( seq ))

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

It has joined a, b, c with hyphen.

str.split()

str dot split open and close parentheses

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

Type as shown press Enter

print str dot split open and close parentheses press Enter

It has split the string at spaces.

Summary slide

In this tutorial, we have learnt to,

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

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 string and r is integer.

s=”Hello”

t=”World”

r=2

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

1. Write code to assign the given string to 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 here, What is the output of s multiplied by r plus t multiplied by r?

Solutions

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

Forum

Fossee Forum

Textbook Companion

Acknowledgment

http://spoken-tutorial.org

For more details, visit this website.

Thank You

Thank you.