--- a/manipulating-lists/script.rst Wed Nov 17 23:24:57 2010 +0530
+++ /dev/null Thu Jan 01 00:00:00 1970 +0000
@@ -1,238 +0,0 @@
-.. Objectives
-.. ----------
-
-.. Clearly state the objectives of the LO (along with RBT level)
-
-.. Prerequisites
-.. -------------
-
-.. 1. getting started with lists
-.. 2.
-.. 3.
-
-.. Author : Madhu
- Internal Reviewer : Punch
- External Reviewer :
- Language Reviewer : Bhanukiran
- Checklist OK? : <16-11-2010, Anand, OK> [2010-10-05]
-
-Script
-------
-
-{{{ Show the slide containing the title }}}
-
-Hello friends. Welcome to this spoken tutorial on Manipulating Lists.
-
-{{{ Show the slide containing the outline }}}
-
-We have already learnt about Lists in Python. In this tutorial,
-we will learn about more advanced features of Lists in Python like how
-to concatenate two lists, details of slicing and striding of lists,
-methods to sort and reverse lists.
-
-{{{ Shift to terminal and start ipython }}}
-
-To begin with let us start ipython, by typing::
-
- ipython
-
-on the terminal
-
-We already know what Lists are in Python, how to access individual
-elements in the list and some of the functions that can be run on the
-lists like ``max, min, sum, len`` and so on. Now let us learn some of
-the basic operations that can be performed on Lists.
-
-We already know how to access individual elements in a List. But what
-if we have a scenario where we need to get a part of the entire list
-or what we call as a slice of the list? Python supports slicing on
-lists. Let us say I have the list::
-
- primes = [2, 3, 5, 7, 11, 13, 17, 19, 23, 29]
-
-To obtain all the primes between 10 and 20 from the above list of
-primes we say::
-
- primes[4:8]
-
-This gives us all the elements in the list starting from the element
-with the index 4, which is 11 in our list, upto the element with index 8
-in the list but not including the eigth element. So we obtain a slice
-starting from 11 upto 19th. It is a very important to remember that
-whenever we specify a range of elements in Python the start index is
-included and end index is not included. So in the above case, 11 which
-was the element with the index 4 was included but 23 which was the
-element with index 8 was excluded.
-
-Following is an exercise you must do.
-
-%% %% Obtain the primes less than 10, from the list ``primes``.
-
-Please, pause the video here, do the exercise and then resume.
-
-::
-
- primes[0:4]
-
-will give us the primes below 10.
-
-Generalizing, we can obtain a slice of the list "p" from the index
-"start" upto the index "end" but excluding "end" with the following
-syntax
-
-{{{ Show the slide containing p[start:stop] }}}
-
-By default the slice fetches all the elements between start and stop
-including start but not stop. So as to say we obtain all the elements
-between start and stop in steps of one. Python also provides us the
-functionality to specify the steps in which the slice must be
-obtained. Say we have::
-
- num = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13]
-
-If we want to obtain all the odd numbers less than 10 from the list
-``num`` we have to start from element with index 1 upto the index 10 in
-steps of 2::
-
- num[1:10:2]
-
-When no step is specified, it is assumed to be 1. Similarly, there are
-default values for start and stop indices as well. If we don't specify
-the start index it is implicitly taken as the first element of the
-list::
-
- num[:10]
-
-This gives us all the elements from the beginning upto the 10th
-element but not including the 10th element in the list "num". Similary
-if the stop index is not specified it is implicitly assumed to be the
-end of the list, including the last element of the list::
-
- num[10:]
-
-gives all the elements starting from the 10th element in the list
-"num" upto the final element including that last element. Now::
-
- num[::2]
-
-gives us all the even numbers in the list "num".
-
-Following is an exercise that you must do.
-
-%% %% Obtain all the multiples of three from the list ``num``.
-
-Please, pause the video here. Do the exercise and then continue.
-
-::
-
- num[::3]
-
-gives us all the multiples of 3 from the list, since every third
-element in it, starting from 0, is divisible by 3.
-
-The other basic operation that we can perform on lists is concatenation
-of two or more lists. We can combine two lists by using the "plus"
-operator. Say we have
-
-{{{ Read as you type }}}::
-
- a = [1, 2, 3, 4]
- b = [4, 5, 6, 7]
- a + b
-
-When we concatenate lists using the "plus" operator we get a new
-list. We can store this list in a new variable::
-
- c = a + b
- c
-
-It is important to observe that the "plus" operator always returns a
-new list without altering the lists being concatenated in any way.
-
-We know that a list is a collection of data. Whenever we have a
-collection we run into situations where we want to sort the
-collection. Lists support sort method which sorts the list inplace::
-
- a = [5, 1, 6, 7, 7, 10]
- a.sort()
-
-Now the contents of the list ``a`` will be::
-
- a
- [1, 5, 6, 7, 7, 10]
-
-As the sort method sorts the elements of a list, the original list we had
-is overwritten or replaced. We have no way to obtain the original list
-back. One way to avoid this is to keep a copy of the original list in
-another variable and run the sort method on the list. However Python
-also provides a built-in function called sorted which sorts the list
-which is passed as an argument to it and returns a new sorted list::
-
- a = [5, 1, 6, 7, 7, 10]
- sorted(a)
-
-We can store this sorted list another list variable::
-
- sa = sorted(a)
-
-Python also provides the reverse method which reverses
-the list inplace::
-
- a = [1, 2, 3, 4, 5]
- a.reverse()
-
-reverses the list "a" and stores the reversed list inplace i.e. in "a"
-itself. Lets see the list "a"::
-
- a
- [5, 4, 3, 2, 1]
-
-But again the original list is lost.
-.. #[punch: removed reversed, since it returns an iterator]
-
-To reverse a list, we could use striding with negative indexing.::
-
- a[::-1]
-
-We can also store this new reversed list in another list variable.
-
-Following is an (are) exercise(s) that you must do.
-
-%% %% Given a list of marks of students in an examination, obtain a
- list with marks in descending order.
- ::
-
- marks = [99, 67, 47, 100, 50, 75, 62]
-
-Please, pause the video here. Do the exercise(s) and then continue.
-
-::
-
- sorted(marks)[::-1]
-
-OR
-
-::
-
- sorted(marks, reverse = True)
-
-
-
-{{{ Show summary slide }}}
-
-This brings us to the end of another session. In this tutorial session
-we learnt
-
- * Obtaining parts of lists using slicing and striding
- * List concatenation
- * Sorting lists
- * Reversing lists
-
-{{{ Show the "sponsored by FOSSEE" slide }}}
-
-This tutorial was created as a part of FOSSEE project, NME ICT, MHRD India
-
-Hope you have enjoyed and found it useful.
-Thank you!
-
-