.. Objectives
.. ----------
.. By the end of this tutorial, you will be able to
.. Create Lists.
.. Access List elements.
.. Append elemets to list
.. Delete list elemets
.. 1. getting started with ipython
.. Prerequisites
.. -------------
.. 1. getting started with strings
.. #. getting started with lists
.. #. basic datatypes
.. Author : Amit
Internal Reviewer : Anoop Jacob Thomas <anoop@fossee.in>
External Reviewer :
Language Reviewer : Bhanukiran
Checklist OK? : <put date stamp here, if OK> [2010-10-05]
.. #[[Anoop: Slides contain only outline and summary
Script
------
{{{ Show the slide containing title }}}
Hello friends and welcome to the tutorial on getting started with
lists.
{{{ Show the slide containing the outline slide }}}
In this tutorial we will be getting acquainted with a python data
structure called lists. We will learn ::
* How to create lists
* Structure of lists
* Access list elements
* Append elements to lists
* Delete elements from lists
List is a compound data type, it can contain data of mutually
different datatypes. List is also a sequence data type, all the
elements are arranged in a given order.
.. #[[Anoop: "all the elements are in order and **there** order has a
meaning." - I guess something is wrong here, I am not able to
follow this.]]
We will first create an empty list with no elements. On your IPython
shell type ::
empty = []
type(empty)
This is an empty list without any elements.
.. #[[Anoop: the document has to be continous, without any
subheadings, removing * Filled lists]]
Lets now see how to define a non-empty list. We do it as,::
nonempty = ['spam', 'eggs', 100, 1.234]
Thus the simplest way of creating a list is typing out a sequence
of comma-separated values (or items) between two square brackets.
As we can see lists can contain different kinds of data. In the
previous example 'spam' and 'eggs' are strings whereas 100 and 1.234 are
integer and float respectively. Thus we can put elements of different types in
lists including lists itself. This property makes lists heterogeneous
data structures.
.. #[[Anoop: the sentence "Thus list themselves can be one of the
element types possible in lists" is not clear, rephrase it.]]
Example ::
listinlist=[[4,2,3,4],'and', 1, 2, 3, 4]
We access an element of a list using its corresponding index. Index of
the first element of a list is 0. So for the list nonempty, nonempty[0]
gives the first element, nonempty[1] the second element and so on and
nonempty[3] the last element. ::
nonempty[0]
nonempty[1]
nonempty[3]
Following is an exercise that you must do.
%% %% What happens when you do nonempty[-1].
Please, pause the video here. Do the exercise and then continue.
.. #[[Anoop: was negative indices introduced earlier, if not may be we
can ask them to try out nonempty[-1] and see what happens and then
tell that it gives the last element in the list.]]
As you can see you get the last element which is 1.234.
In python negative indices are used to access elements from the end::
nonempty[-1]
nonempty[-2]
nonempty[-4]
-1 gives the last element which is the 4th element , -2 second to last
and -4 gives the fourth from the last which, in this case, is the first element.
We can append elements to the end of a list using the method append. ::
nonempty.append('onemore')
nonempty
nonempty.append(6)
nonempty
Following are exercises that you must do.
%% %% What is the syntax to get the element 'and'
in the list,listinlist ?
%% %% How would you get 'and' using negative indices?
Please, pause the video here. Do the exercise and then continue.
The solution is on your screen
As we can see nonempty is appended with 'onemore' and 6 at the end.
Using len function we can check the number of elements in the list
nonempty. In this case it is 6 ::
len(nonempty)
Just like we can append elements to a list we can also remove them.
There are two ways of doing it. One is by using index. ::
del(nonempty[1])
deletes the element at index 1, i.e the second element of the
list, 'eggs'. The other way is removing element by content. Lets say
one wishes to delete 100 from nonempty list the syntax of the command
would be
.. #[[Anoop: let x = [1,2,1,3]
now x.remove(x[2])
still x is [2,1,3] so that is not the way to remove
element by index, it removed first occurrence of 1(by
content) and not based on index, so make necessary
changes]]
::
nonempty.remove(100)
but what if there were two 100's. To check that lets do a small
experiment. ::
nonempty.append('spam')
nonempty
nonempty.remove('spam')
nonempty
If we check now we will see that the first occurence 'spam' is removed
and therefore `remove` removes the first occurence of the element in the sequence
and leaves others untouched.
One should remember this that while del removes by index number,
`remove` removes on the basis of content being passed on. For instance
if ::
k = [1,2,1,3]
del([k[2])
gives us [1,2,3]. ::
k.remove(x[2])
will give us [2,1,3]. Since it deletes the first occurence of what is
returned by x[2] which is 1.
.. #[[Anoop: does it have two spams or two pythons?]]
.. #[[Anoop: there are no exercises/solved problems in this script,
add them]]
Following are exercises that you must do.
%% %% Remove the third element from the list, listinlist.
%% %% Remove 'and' from the list, listinlist.
Please, pause the video here. Do the exercise and then continue.
{{{Slide for Summary }}}
In this tutorial we came across a sequence data type called lists. ::
* We learned how to create lists.
* How to access lists.
* Append elements to list.
* Delete Element from list.
* And Checking list length.
{{{ show Sponsored by Fossee Slide }}}
This tutorial was created as a part of FOSSEE project.
I hope you found this tutorial useful.
Thank You
..
* Author : Amit Sethi
* First Reviewer :
* Second Reviewer : Nishanth