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+.. Objectives
+.. ----------
+
+.. At the end of this tutorial, you will be able to
+
+.. 1. Write blocks of code in python.
+.. #. Use for loop.
+.. #. Use ``range()`` function.
+.. #. Write blocks in python interpreter
+.. #. Write blocks in ipython interpreter.
+
+
+.. Prerequisites
+.. -------------
+
+.. 1. should have ``ipython`` and ``pylab`` installed.
+.. #. getting started with ``ipython``.
+.. #. getting started with lists.
+
+
+.. Author : Anoop Jacob Thomas <anoop@fossee.in>
+ Internal Reviewer : Nishanth
+ Internal Reviewer(2): Amit
+ External Reviewer :
+ Language Reviewer : Bhanukiran
+ Checklist OK? : <10-11-2010, Anand, OK> [2010-10-05]
+
+
+=============================
+Getting started with for loop
+=============================
+
+{{{ show welcome slide }}}
+
+Hello and welcome to the tutorial `Getting started with ``for`` loop`.
+
+{{{ switch to next slide, outline slide }}}
+
+In this tutorial we will learn about ``for`` loops in python, and also
+learn how to write blocks of code in Python.
+
+.. #[Nishanth]: Instead of saying basics of indenting code,
+ say How to define code blocks in Python
+
+{{{ switch to next slide, about whitespaces }}}
+
+In Python whitespace is significant, and the blocks are visually
+separated.
+
+.. #[nishanth]: Simply tell how blocks are defined in python.
+ The details like braces are not used and its
+ advantages like neat code can be told after completely
+ explaining the indentation
+
+.. #[Amit]: Do you want to do that here. May be its better to talk about
+ this after some initiation into the idea of blocks.
+
+The best practice is to indent the code using four spaces.
+
+.. #[Nishanth]: Even this detail may be skipped. Simply say use 4 spaces
+ for indentation. Do that while typing so that they can
+ actually see what is being typed.
+
+As you can see in the slide, ``Block B`` is an inner block and it is
+indented using 4 spaces, and after ``Block B`` the next statement in
+``Block A`` starts from the same indentation level of other ``Block
+A`` statements.
+
+Now let us move straight into ``for`` loop.
+
+{{{ switch to next slide, problem statement of exercise 1 }}}
+
+
+Write a for loop which iterates through a list of numbers and find the
+square root of each number.
+::
+
+ numbers are 1369, 7225, 3364, 7056, 5625, 729, 7056, 576, 2916
+
+.. #[nishanth]: making new list with square roots induces extra complication
+ like appending which has no use case here
+
+.. #[Nishanth]: The problem focuses more on square root and creation
+ of list. The problem must be simple and focusing on
+ nothing more but the indentation and for loop.
+ May be change the problem to print squares than to
+ print square roots.
+
+For the problem, first we need to create a ``list`` of numbers and
+then iterate over the list and find the square root of each element in
+it. And let us create a script, rather than typing it out in the
+interpreter itself. Create a script called list_roots.py and type the
+following.
+
+{{{ open the text editor and paste the following code there }}}
+::
+
+ numbers = [1369, 7225, 3364, 7056, 5625, 729, 7056, 576, 2916]
+ for each in numbers:
+ print "Square root of", each, "is", sqrt(each)
+ print "This is not in for loop!"
+
+.. numbers = [1, 12, 3, 4, 21, 17]
+ for each in numbers:
+ print each, each * each
+
+.. #[nishanth]: I don't see a use case to append the sq_root to
+ square_roots. It is only complicating stuff.
+ Simply iterate and print.
+
+{{{ switch to next slide, save and run script }}}
+
+{{{ save the script }}}
+
+Now save the script, and run it from your IPython interpreter. I
+assume that you have started your IPython interpreter using ``-pylab``
+option.
+
+Run the script as,
+::
+
+ %run -i list_roots.py
+
+.. #[Nishanth]: you don't have to use the -i option here
+
+{{{ run the script }}}
+
+So that was easy! All what we did was iterate over the list element by
+element and then use the element for calculation. Note that here we
+used two variables. One the variable ``numbers``, which is a list,
+another one ``each``, which is the element of list under consideration
+in each cycle of the ``for`` loop. The variable names can be chosen by
+you.
+
+.. #[Nishanth]: The details like we didn't have to find the length
+ are relevant for people who have programmed in C or
+ other languages earlier. But for a newbie it is more
+ of confusing extra info. That part may be skipped.
+ Simply go ahead and focus on the syntax of for loop.
+ And how the variable name is used inside the for loop.
+ If you modify the question to only print, the extra
+ variable sq_root can also be avoided. let it be more
+ about "each", "numbers" and "for". no other new names.
+
+{{{ show the script which was created }}}
+
+Note that the lines after ``for`` statement, is indented using four
+spaces.
+
+{{{ highlight the line after for statement }}}
+
+It means that line is part of the for loop. And it is a block of code,
+although it is only a single statement in the block. And the fourth
+line or the immediate line after the ``for`` block is not indented,
+
+{{{ highlight the fourth line - the line just after for loop }}}
+
+it means that it is not part of the ``for`` loop and the lines after
+that doesn't fall in the scope of the ``for`` loop. Thus each block is
+separated by the indentation level and that marks the importance of
+white-spaces in Python.
+
+{{{ switch to the slide which shows the problem statement of the first
+problem to be tried out }}}
+
+Now a question for you to try, from the given numbers make a list of
+perfect squares and a list of those which are not. The numbers are,
+::
+
+ 7225, 3268, 3364, 2966, 7056, 5625, 729, 5547, 7056, 576, 2916
+
+Pause here and try to solve the problem before proceeding further.
+
+{{{ switch to next slide, problem statement of second problem in
+solved exercise}}}
+
+Now let us try a simple one, to print the square root of numbers in
+the list. And this time let us do it right in the IPython
+interpreter.
+
+{{{ switch to next slide, Indentation in ``ipython`` }}}
+
+{{{ switch focus to the IPython interpreter }}}
+
+So let us start with making a list. Type the following
+::
+
+ numbers = [1369, 7225, 3364, 7056, 5625, 729, 7056, 576, 2916]
+ for each in numbers:
+
+and now you will notice that, as soon as you press the return key
+after for statement, the prompt changes to four dots and the cursor is
+not right after the four dots but there are four spaces from the
+dots. Please note that IPython automatically indents the block. The
+four dots tell you that you are inside a block. Now type the rest of
+the ``for`` loop,
+
+{{{ switch to next slide, Indentation in ``ipython`` (cont'd) }}}
+
+.. #[Nishanth]: Tell that IPython does auto indentation.
+
+::
+
+ print "Square root of", each,
+ print "is", sqrt(each)
+
+Now we have finished the statements in the block, and still the
+interpreter is showing four dots, this means that you are still inside the
+block. To exit from the block press the return key or the enter key twice
+without entering anything else. It printed the square root of each
+number in the list, and that is executed in a ``for`` loop.
+
+{{{ switch to next slide, Indentation in ``python`` interpreter }}}
+
+Now, let us find the cube of all the numbers from one to ten. But this
+time let us try it in the vanilla version of Python interpreter.
+
+Start the vanilla version of Python interpreter by issuing the command
+``python`` in your terminal.
+
+{{{ open the python interpreter in the terminal using the command
+python to start the vanilla Python interpreter }}}
+
+{{{ switch to next slide, Indentation in ``python`` interpreter
+(cont'd) }}}
+
+Start with,
+::
+
+ for i in range(1,11):
+
+and press enter once, and we will see that this time it shows four
+dots, but the cursor is close to the dots, so we have to indent the
+block. The vanilla version of Python interpreter does not indent the
+code automatically. So enter four spaces there and then type the
+following
+::
+
+ print i, "cube is", i**3
+
+Now when we hit enter, we still see the four dots, to get out of the
+block, hit enter once again
+
+.. #[Nishanth]: Here also the overhead on print can be reduced.
+ Think of a simple print statement. This statement
+ will be confusing for a newbie.
+ We can focus more on indentation in python.
+
+.. #[nishanth]: Not sure if you must use range here. You can
+ define a list of numbers and iterate on it.
+ Then say this list can also be generated using
+ the range function and hence introduce range.
+
+{{{ switch to the next slide, ``range()`` function }}}
+
+Okay! so the main thing that we learned here is how to use Python
+interpreter and IPython interpreter to specify blocks. But while we
+were generating the multiplication table we used something new,
+``range()`` function. ``range()`` is an inbuilt function in Python
+which can be used to generate a ``list`` of integers from a starting
+number to an ending number. Note that the ending number that you
+specify will not be included in the ``list``.
+
+.. #[Nishanth]: Show some examples of range without the step argument
+ May be give an exercise with negative numbers as arguments
+
+{{{ switch to next slide, problem statement of the next problem in
+solved exercises }}}
+
+Now, let us print all the odd numbers from 1 to 50. Pause here and try
+to solve the problem yourself.
+
+Let us do it in our IPython interpreter for ease of use.
+
+{{{ switch focus to ipython interpreter }}}
+
+The problem can be solved by just using the ``range()`` function.
+
+It can be solved as,
+::
+
+ print range(1,51,2)
+
+This time we passed three parameters to ``range()`` function unlike
+the previous case where we passed only two parameters. The first two
+parameters are the same in both the cases. The first parameter is the
+starting number of the sequence and the second parameter is the end of
+the range. Note that the sequence doesn't include the ending
+number. The third parameter is for stepping through the sequence. Here
+we gave two which means we are skipping every alternate element.
+
+{{{ switch to next slide, summary slide }}}
+
+Thus we come to the end of this tutorial. We learned about blocks in
+Python, indentation, blocks in IPython, for loop, iterating over a
+list and then the ``range()`` function.
+
+.. #[Amit]: There does seem to too much overhead of details. Should
+ the first example be done using script is it necessary.
+ Do add some things in evolutionary manner. Like introducing
+ range as a list and doing a very very simple for loop.Like
+ iterating over [1,2,3] .Before getting into a problem.
+ And club details about problem in one paragraph and syntactic details
+ in other.
+
+{{{ switch to next slide, thank you slide }}}
+
+Thank you!