1 .. Objectives

     2 .. ----------

     3 

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

     5 

     6 ..   1. How to define strings

     7 ..   #. Different ways of defining a string

     8 ..   #. How to concatenate strings 

     9 ..   #. How to print a string repeatedly 

    10 ..   #. Accessing individual elements of the string

    11 ..   #. Immutability of strings

    12 

    13 .. Prerequisites

    14 .. -------------

    15 

    16 .. 1. getting started with ipython

    17      

    18 .. Author              : Madhu

    19    Internal Reviewer   : 

    20    External Reviewer   :

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

    22 

    23 Script

    24 ------

    25 

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

    27 

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

    29 strings.

    30 

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

    32 

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

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

    35 some of the operations that can be performed on strings.

    36 

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

    38 

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

    40 

    41   ipython

    42 

    43 on the terminal

    44 

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

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

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

    48 within the quotes

    49 

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

    51 

    52   'This is a string'

    53   "This is a string too'

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

    55   """This is also a string"""

    56   'p'

    57 

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

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

    60 string. For example::

    61 

    62   "Python's string manipulation functions are very useful"

    63 

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

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

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

    67 very handy feature.

    68 

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

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

    71 string no matter how many lines it extends::

    72 

    73    """Having more than one control character to define

    74    strings come as very handy when one of the control

    75    characters itself is part of the string."""

    76 

    77 We can assign this string to any variable::

    78 

    79   a = 'Hello, World!'

    80 

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

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

    83 are applicable to any other immutable collection in Python works on

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

    85 

    86   a = 'Hello'

    87   b = 'World'

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

    89 

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

    91 the same statement. The addition operation performs the concatenation

    92 of two strings.

    93 

    94 Similarly we can multiply a string with an integer::

    95 

    96   a = 'Hello'

    97   a * 5

    98 

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

   100 5 times.

   101 

   102 Since strings are collections we can access individual items in the

   103 string using the subscripts::

   104 

   105   a[0]

   106 

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

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

   109 access the strings from the end using negative indices::

   110 

   111   a[-2]

   112 

   113 gives us second element from the end of the string

   114 

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

   116 

   117   a = 'hello'

   118   a[0] = 'H'

   119 

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

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

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

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

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

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

   126 into a single string based on the specified separator.

   127 

   128 {{{ Show summary slide }}}

   129 

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

   131 we learnt

   132 

   133   * How to define strings

   134   * Different ways of defining a string

   135   * String concatenation and repeatition

   136   * Accessing individual elements of the string

   137   * Immutability of strings

   138 

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

   140 

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

   142 

   143 Hope you have enjoyed and found it useful.

   144 Thank you!

   145