.. Objectives

.. ----------

.. At the end of this tutorial, you should know --

..   1. How to define strings

..   #. Different ways of defining a string

..   #. How to concatenate strings 

..   #. How to print a string repeatedly 

..   #. Accessing individual elements of the string

..   #. Immutability of strings

.. Prerequisites

.. -------------

.. 1. getting started with ipython

.. Author              : Madhu

   Internal Reviewer   : 

   External Reviewer   :

   Checklist OK?       : <put date stamp here, if OK> [2010-10-05]

Script

------

{{{ Show the slide containing the title }}}

Hello friends. Welcome to this spoken tutorial on Getting started with

strings.

{{{ Show the slide containing the outline }}}

In this tutorial, we will learn what do we actually mean by strings in

python, how python supports the use of strings. We will also learn

some of the operations that can be performed on strings.

{{{ Shift to terminal and start ipython }}}

To begin with let us start ipython, by typing::

  ipython

on the terminal

So what are strings? In Python anything within either single quotes

or double quotes or triple single quotes or triple double quotes are

strings. This is true whatsoever, even if there is only one character

within the quotes

{{{ Type in ipython the following and read them as you type }}}::

  'This is a string'

  "This is a string too'

  '''This is a string as well'''

  """This is also a string"""

  'p'

Having more than one control character to define strings come as very

handy when one of the control characters itself is part of the

string. For example::

  "Python's string manipulation functions are very useful"

In this case we use single quote for apostrophe. If we had only single

quote to define strings we should have a clumsy way of escaping the

single quote character to make it part of the string. Hence this is a

very handy feature.

The triple quoted strings let us define multi-lines strings without

using any escaping. Everything within the triple quotes is a single

string no matter how many lines it extends::

   """Having more than one control character to define

   strings come as very handy when one of the control

   characters itself is part of the string."""

We can assign this string to any variable::

  a = 'Hello, World!'

Now 'a' is a string variable. String is a collection of characters. In

addition string is an immutable collection. So all the operations that

are applicable to any other immutable collection in Python works on

string as well. So we can add two strings::

  a = 'Hello'

  b = 'World'

  c = a + ', ' + b + '!'

We can add string variables as well as the strings themselves all in

the same statement. The addition operation performs the concatenation

of two strings.

Similarly we can multiply a string with an integer::

  a = 'Hello'

  a * 5

gives another string in which the original string 'Hello' is repeated

5 times.

Since strings are collections we can access individual items in the

string using the subscripts::

  a[0]

gives us the first character in the string. The indexing starts from 0

for the first character up to n-1 for the last character. We can

access the strings from the end using negative indices::

  a[-2]

gives us second element from the end of the string

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

  a = 'hello'

  a[0] = 'H'

As said earlier, strings are immutable. We cannot manipulate the

string. Although there are some methods which let us to manipulate the

strings. We will look at them in the advanced session on strings. In

addition to the methods that let us manipulate the strings we have

methods like split which lets us break the string on the specified

separator, the join method which lets us combine the list of strings

into a single string based on the specified separator.

{{{ Show summary slide }}}

This brings us to the end of another session. In this tutorial session

we learnt

  * How to define strings

  * Different ways of defining a string

  * String concatenation and repeatition

  * Accessing individual elements of the string

  * Immutability of strings

{{{ Show the "sponsored by FOSSEE" slide }}}

This tutorial was created as a part of FOSSEE project, NME ICT, MHRD India

Hope you have enjoyed and found it useful.

Thank you!