22     In this tutorial we shall look at data types available in Python and 

    22     In the previous tutorial we have looked at data types for dealing

    23     how to perform simple Input and Output operations. 

    23     with numbers. In this tutorial we shall look at strings. We shall

    24     for 'Numbers' we have: int, float, complex datatypes

    24     look at how to do elementary string manipulation, and simple input

    25     for Text content we have strings.

    25     and output operations. 

    26     For conditional statements, 'Booleans'.

    28     Now we shall look at Python Strings.

    27     As, we have seen in previous tutorials, anything enclosed within

    29     In python anything enclosed inside quotes(single or double) is a string

    28     quotes is a string. For example -

    30     so 

    29 

    40     Similar to lists we covered earlier even string elements can be accessed 

    47     Like lists, which we already saw, string elements can be accessed

    41     via index numbers starting from 0

    48     with their indexes. The indexing here, also, begins from 0. 

    45     will 

    52 

    46     To access last element we can use a[-1] which is one of Pythons feature.

    53     To access the last element, we can use -1 as the index!

    48     len function works with the strings also as it does with the arrays and 

    55     Similarly, we could access other elements with corresponding -ve

    49     returns length of the string.

    56     indexes. This is a very handy feature of python. 

    57 

    58     The len function, which we used with lists, works with strings too. 

    59     len(a)

    60 

    61     Python's strings support the operations + and *

    62     a + b

    63     a * 4

    64     What do you think would happen when you do a * a?

    65     It's obviously an error since, it doesn't make any logical sense. 

    51     One thing to notice about the string variables is that they are 

    67     One thing to note about strings, is that they are immutable, that

    52     immutable, that is

    68     is 

    54     will throw an error

    70     throws an error

    56     Some of methods available for string are:

    72     Then how does one go about changing strings? Python provides

    73     'methods' for doing various manipulations on strings. For example - 

    74 

    75     a.upper() returns a string with all letters capitalized.

    76 

    77     and a.lower() returns a string with all smaller case letters.

    78 

    58     returns true if initial of the string is same

    80     returns True if the string starts with the argument passed. 

    59     similarly there is endswith

    81 

    82     similarly there's endswith

    61     a.upper() returns a string with all letters capitalized.

    84 

    62     and a.lower() returns a string with all smaller case letters.

    85     We've seen the use of split function in the previous

    63     As we have seen earlier use of split function, it returns the list after

    86     tutorials. split returns a list after splitting the string on the

    64     splitting the string, so

    87     given argument. 

    65     a.split()

    88     alist = a.split()

    66     will give list with three elements.

    89     will give list with four elements.

    67     we also have 'join' function, which does the opposite of what

    90     print alist

    91 

    92     Python also has a 'join' function, which does the opposite of what

    69     ''.join(['a','b','c']) will return a joined string of the list we pass

    94     ' '.join(alist) will return the original string a. 

    70     to it. Since join is performed on '' that is empty string we get 'abc'

    95     '-'.join(alist) will return a string with the spaces in the string

    71     if we do something like

    96     'a' replaced with hyphens. 

    72     '-'.join(['a','b','c'])

    97 

    98     * formatting - printf style *

    99       In []: x, y = 1, 1.234

   100       

   101       In []: 'x is %s, y is %s' %(x, y)

   102       Out[]: 'x is 1, y is 1.234'

   103     * formatting - printf style *

   104 

   105 

   106     Now we shall look at simple input from and output to the

   107     console. 

   108     The raw_input function allows us to give input from the console. 

   109     a = raw_input()

   110     it is now waiting for the user input. 

   111     5

   112     a

   113     raw_input also allows us to give a prompt string, as shown 

   114     a = raw_input("Enter a value: ")

   115     Enter a value: 5

   116     Note that a, is now a string variable and not an integer. 

   117     type(a)

   118     we could use type conversion similar to that shown in the tutorial

   119     on numeric datatypes. 

   120     a = int(a)

   121     a has now been converted to an integer. 

   122     type(a)

   123 

   124     For console output, we use print which is pretty straightforward. 

   125     We shall look at a subtle feature of the print statement. 

   126     We shall first put the following code snippet in the file

   127     "hello1.py"

   128     print "Hello"

   129     print "World"

   130     We save the file and run it from the ipython interpreter. Make

   131     sure you navigate to the place, where you have saved it. 

   132     %run -i hello1.py

   133 

   134     Now we make a small change to the code snippet and save it in the

   135     file named "hello2.py"

   136     print "Hello", 

   137     print "World"

   138     We now run this file, from the ipython interpreter. 

   139     %run -i hello2.py

   140     Note the difference in the output of the two files that we

   141     executed. The comma adds a space at the end of the line, instead

   142     of a new line character that is normally added. 

   143 

   144     Before we wind up, a couple of miscellaneous things. 

   145     As you may have already noticed, Python is a dynamically typed

   146     language, that is you don't have to specify the type of a variable

   147     when using a new one. You don't have to do anything special, to use

   148     a variable that was of int type as a float or string. 

    74     we come to the end of this tutorial on introduction of Data types in

   150     a = 1

   151     a = 1.1

   152     a = "Now I am a string!"

   153 

   154     Comments in Python start with a pound or hash sign. Anything after

   155     a #, until the end of the line is considered a comment, except of

   156     course, if the hash is in a string. 

   157     a = 1 # in-line comments

   158     # a comment line

   159     a = "# not a comment"

   160 

   161     we come to the end of this tutorial on strings introduction of Data types in