Python-3.4.3/C2/Getting-started-with-strings/English
'Python/C2/Getting Started with Strings/English'Title of script: Getting Started with Strings
Author: Trupti Kini
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containing title, name of the production team along with the logo of MHRD |
Hello Friends. Welcome to the tutorial on "Getting Started with Strings". |
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Objectives |
At the end of this tutorial, you will learn to,
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System Specifications |
To record this tutorial, I am using
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Pre-requisites |
To practise this tutorial, you should know how to
If not, see the pre-requisite Python tutorials on this website. |
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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. |
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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. |
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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 |
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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
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[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.
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[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() |
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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
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Highlight ['Line1-abcdef', 'Line2-abc', 'Line4-abcd'] | We get the output like this.
It has split the strings at spaces. |
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Summary slide |
This brings us to the end of this tutorial.
In this tutorial, we have learnt to,
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Evaluation
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
They are assigned with the values as shown below, What is the output of s multiplied by r plus t multiplied by r? |
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Solutions |
And the answers,
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Forum |
Please post your timed queries in this forum. |
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Fossee Forum |
Please post your general queries on Python in this forum. |
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Textbook Companion |
FOSSEE team coordinates the TBC project. |
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Acknowledgment |
Spoken Tutorial Project is funded by NMEICT, MHRD, Govt. of India.
For more details, visit this website. |
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Thank You |
This is Trupti Kini from IIT Bombay signing off.
Thank you. |