1 ========

     2  Script

     3 ========

     4 

     5 Welcome to so and so..

     6 

     7 

     8 This tutorial will cover the basic usage of the ``ipython``

     9 interpreter. The following topics would be covered.

    10 

    11 {{{ Show slide with outline of the session. }}}

    12 

    13 IPython is an enhanced Python interpreter that provides features like

    14 tabcompletion, easier access to help and many other functionalities

    15 which are not available in the vannila Python interpreter.

    16 

    17 First let us see how to invoke the ``ipython`` interpreter.

    18 

    19 We type

    20 ::

    21 

    22   ipython

    23 

    24 at the terminal prompt to invoke the ipython interpreter.

    25 

    26 We get a prompt with ``In [1]:`` after getting some information about

    27 the version of Python installed and some help commands.   

    28 

    29 If you get an error saying something like ``ipython is not

    30 installed``, refer to the tutorial on how to install the packages

    31 required for this course.

    32 

    33 Now, to quit the ipython interpreter, type Ctrl-D.  You are prompted

    34 asking if you really want to exit, type y to say yes and quit ipython.

    35 

    36 Start ipython again, as you did before.

    37 

    38 The prompt that you have says ``In [1]``. ``In`` stands for input and the

    39 ipython interpreter is ready to accept input from you.

    40 

    41 Now let us see, how we can type some commands into the interpreter.

    42 

    43 Start with the simplest thing, addition.

    44 

    45 Let's type 

    46 ::

    47   1+2 

    48 

    49 at the prompt. IPython promptly gives back the output as 3.  Notice

    50 that the output is displayed with an ``Out[1]`` indication.

    51 

    52 Let's try out few other mathematical operations.

    53 ::

    54 

    55   5 - 3

    56   7 - 4

    57   6 * 5

    58 

    59 Now let's ``print 1+2``. Instead of typing the whole thing, we make

    60 use of the fact that IPython remembers the history of the commands

    61 that you have already used. We use the up arrow key to go back the

    62 command ``1+2``. We then use the left-arrow key to navigate to the

    63 beginning of the line and add the word ``print`` and a space. Then hit

    64 enter and observe that the interpreter prints out the value as 3,

    65 without the Out[] indication.

    66 

    67 Now, let's change the previous command ``print 1+2`` to ``print

    68 10*2``.  We use the up arrow again to navigate to the previous command

    69 and use the left arrow key to move the cursor on to the + symbol and

    70 then use the delete key to remove it and type 0 and * to change the

    71 expression to the required one.  We hit enter to see the output of

    72 ``print``. 

    73 

    74 Now, let's say we want to use the function ``round``. We type ``ro``

    75 at the prompt and hit the tab key. As you can see, the IPython

    76 completes the command. This feature is called the tab-completion.

    77 

    78 Now, we remove all the characters and just type ``r`` and then hit

    79 tab. IPython does not complete the command since there are many

    80 possibilities. It just lists out all the possible completions.

    81 

    82 %% %% Pause the video here and type ``ab`` and hit tab to see what

    83 happens. Next, jut type ``a`` and hit tab to see what happens. 

    84 

    85 ``ab`` tab completes to ``abs`` and ``a<tab>`` gives us a list of all

    86 the commands starting with a. 

    87 

    88 Now, let's see what these functions are used for.  We will use the

    89 help features of ipython to find this out.

    90 

    91 To get the help of any function, we first type the function, ``abs``

    92 in our case and then add a ? at the end and hit enter.

    93 

    94 As the documentation says, ``abs`` accepts a number as an input and

    95 returns it's absolute value.

    96 

    97 We say, 

    98 ::

    99 

   100   abs(-19)

   101 

   102   abs(19)

   103 

   104 We get 19, as expected, in both the cases.  

   105 

   106 Does it work for decimals (or floats)?  Let's try typing abs(-10.5)

   107 and we do get back 10.5.

   108 

   109 %% %% Pause the video here, and look-up the documentation of ``round``

   110 and see how to use it. 

   111 

   112 ::

   113 

   114  round?

   115 

   116 If you notice, there are extra square brackets around the ``ndigits``.

   117 This means that ``ndigits`` is optional and 0 is the default value.

   118 Optional parameters are shown in square brackets anywhere in Python

   119 documentation.

   120 

   121 The function ``round``, rounds a number to a given precision.

   122 

   123 %% %% Pause the video here and check the output of

   124 round(2.48)

   125 round(2.48, 1)

   126 round(2.48, 2)

   127 and then resume the video. 

   128 

   129 ::

   130   round(2.484)

   131   round(2.484, 1)

   132   round(2.484, 2)

   133 

   134 We get 2.0, 2.5 and 2.48, which are what we expect. 

   135 

   136 Let's now see how to correct typing errors that we make when typing at

   137 the terminal. As already shown, if we haven't hit the enter key

   138 already, we could navigate using the arrow keys and make deletions

   139 using delete or backspace key and correct the errors. 

   140 

   141 Let's now type round(2.484 and hit enter, without closing the

   142 parenthesis. We get a prompt with dots.  This prompt is the

   143 continuation prompt of ``ipython``.  It appears, the previous line is

   144 incomplete in some way.  We now complete the command by typing, the

   145 closing parenthesis and hitting enter.  We get the expected output of

   146 2.5. 

   147 

   148 In other instances, if we commit a typing error with a longer and more

   149 complex expression and end up with the continuation prompt, we can

   150 type Ctrl-C to interrupt the command and get back the ``ipython`` input

   151 prompt.

   152 

   153 %% %% Pause the video here. 

   154 Try typing round(2.484, and hit enter. and then cancel the command

   155 using Ctrl-C. Then, type the command, round(2.484, 2) and resume the

   156 video. 

   157 

   158 ::

   159   

   160   round(2.484 

   161   ^C

   162 

   163   round(2.484, 2)

   164   

   165 This brings us to the end of the tutorial on getting started with

   166 ``ipython``.

   167 

   168 In this tutorial we have seen 

   169 {{{ show the outline/summary slide. }}}

   170 

   171 Thank you!

   172 

   173 

   174