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+.. 3.2 LO: getting started with =for= (2) [anoop]
+.. -----------------------------------------------
+.. * blocks in python
+.. + (indentation)
+.. * blocks in ipython
+.. + ... prompt
+.. + hitting enter
+.. * =for= with a list
+.. * =range= function
+
+=============================
+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 see ``for`` loops in python, and also cover
+the basics of indenting code in python.
+
+{{{ switch to next slide, about whitespaces }}}
+
+In Python whitespace is significant, and the blocks are visually
+separated rather than using braces or any other mechanisms for
+defining blocks. And by this method Python forces the programmers to
+stick on to one way of writing or beautifying the code rather than
+debating over where to place the braces. This way it produces uniform
+code than obscure or unreadable code.
+
+A block may be defined by a suitable indentation level which can be
+either be a tab or few spaces. And the best practice is to indent the
+code using four spaces.
+
+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. Also make a new list with the square roots
+and print it at the end.
+::
+
+ numbers are 1369, 7225, 3364, 7056, 5625, 729, 7056, 576, 2916
+
+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]
+ square_roots = []
+ for each in numbers:
+ sq_root = sqrt(each)
+ print "Square root of", each, "is", sq_root
+ square_roots.append(sq_root)
+ print
+ print square_roots
+
+{{{ 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
+
+{{{ run the script }}}
+
+So that was easy! We didn't have to find the length of the string nor
+address of each element of the list one by one. All what we did was
+iterate over the list element by element and then use the element for
+calculation. Note that here we used three 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,
+and then a variable ``sq_root`` for storing the square root in each
+cycle of the ``for`` loop. The variable names can be chosen by you.
+
+{{{ show the script which was created }}}
+
+Note that three lines after ``for`` statement, are indented using four
+spaces.
+
+{{{ highlight the threee lines after for statement }}}
+
+It means that those three lines are part of the for loop. And it is
+called a block of statements. And the seventh line or the immediate
+line after the third line in the ``for`` loop is not indented,
+
+{{{ highlight the seventh 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. Thus marking 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
+
+{{{ switch to next slide, problem statement of second problem in
+solved exercie}}}
+
+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 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. The four dots tell you that you are inside a block. Now type the
+rest of the ``for`` loop,
+::
+
+ sq_root = sqrt(each)
+ print "Square root of", each, "is", sq_root
+
+Now we have finished the statements in the block, and still the
+interpreter is showing four dots, which means you are still inside the
+block. To exit from the block press 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.
+
+Now, let us generate the multiplication table of 10 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 }}}
+
+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 intend the
+block. So enter four spaces there and then type the following
+::
+
+
+ print "10 *",i,"=",i*10
+
+Now when we hit enter, we still see the four dots, to get out of the
+block type enter once.
+
+Okay! so the main thing here we learned 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
+range to an ending range. Note that the ending number that you specify
+will not be included in the ``list``.
+
+Now, let us print all the odd numbers from 1 to 50. Let us do it in
+our IPython interpreter for ease of use.
+
+{{{ switch focus to ipython interpreter }}}
+
+{{{ switch to next slide, problem statement of the next problem in
+solved exercises }}}
+
+Print the list of odd numbers from 1 to 50. It will be better if
+you can try it out yourself.
+
+It is a very trivial problem and 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, recap 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.
+
+{{{ switch to next slide, thank you slide }}}
+
+Thank you!
+
+.. Author: Anoop Jacob Thomas <anoop@fossee.in>
+ Reviewer 1:
+ Reviewer 2:
+ External reviewer: