--- a/conditionals.rst Wed Oct 13 11:13:46 2010 +0530
+++ /dev/null Thu Jan 01 00:00:00 1970 +0000
@@ -1,176 +0,0 @@
-Hello friends. Welcome to this spoken tutorial on Getting started with
-strings.
-
-{{{ Show the slide containing the title }}}
-
-{{{ Show the slide containing the outline }}}
-
-In this tutorial, we will learn the basic conditional constructs
-available in Python. We learn the if/else, if/elif/else and ternary
-conditional constructs available in Python.
-
-{{{ Shift to terminal and start ipython }}}
-
-To begin with let us start ipython, by typing::
-
- ipython
-
-on the terminal
-
-Whenever we have two possible states that can occur depending on a
-whether a certain condition we can use if/else construct in
-Python. Say for example we have a variable "a" which stores integers
-and we are required to find out whether the value of the variable "a"
-is an even number or an odd number. To test out conditional statements
-as an example, let us say the value of the variable "a" is 5::
-
- a = 5
-
-In such a case we can write the if/else block as::
-
- if a % 2 == 0:
- print "Even"
- else:
- print "Odd"
-
-When the value of the variable "a" is divided by 2 and the remainder
-is 0 i.e. the result of the operation "a modulo 2" is 0 the condition
-"a % 2 == 0" evaluates to True, so the code within the if block gets
-executed. This means that the value of "a" is Even.
-
-If the operation "a modulo 2" is not 0 the condition "a % 2 == 0"
-evaluates to False and hence the code block within else gets executed
-which means that the value of "a" is Odd.
-
-Note in such a case only one of the two blocks get executed depending
-on whether the condition is True or False.
-
-There is a very important sytactic element to understand here. All the
-statements which are inside a certain code block are indented by 4
-spaces. The statement which starts a new code block after it, i.e. the
-if statement in this example ends with a colon (:). So the next
-immediate line will be inside the if block and hence indented by 4
-spaces. To come out of the code block we have to come back to the
-previous indentation level as shown in the else line here. Again the
-line following else will be in a new block so else line ends with a
-colon and the following block of code is indented by 4.
-
-As we use if/else statement when we have a condition which can take
-one of the two states, we may have conditions which can take more than
-two states. In such a scenario Python provides if/elif/else
-statements. Let us take an example. We have a variable "a" which holds
-integer values. We need to print "positive" if the value of a is
-positive, "negative" if it is negative and "zero" if the value of the
-variable "a" is 0. Let us use if/elif/else ladder for it. For the
-purposes of testing our code let us assume that the value of a is -3::
-
- a = -3
-
- if a > 0:
- print "positive"
- elif a < 0:
- print "negative"
- else:
- print "zero"
-
-This if/elif/else ladder is self explanatory. All the syntax and rules
-as said for if/else statements hold. The only addition here is the
-elif statement which can have another condition of its own.
-
-Here, exactly one block of code is executed and that block of code
-corresponds to the condition which first evaluates to True. Even if
-there is a situation where multiple conditions evaluate to True all
-the subsequent conditions other than the first one which evaluates to
-True are neglected. Consequently, the else block gets executed if and
-only if all the conditions evaluate to False.
-
-Also, the else block in both if/else statement and if/elif/else is
-optional. We can have a single if statement or just if/elif statements
-without having else block at all. Also, there can be any number of
-elif's within an if/elif/else ladder. For example
-
-{{{ Show slide for this }}}
-
- if user == 'admin':
- # Do admin operations
- elif user == 'moderator':
- # Do moderator operations
- elif user == 'client':
- # Do customer operations
-
-{{{ end of slide switch to ipython }}}
-
-is completely valid. Note that there are multiple elif blocks and there
-is no else block.
-
-In addition to these conditional statements, Python provides a very
-convenient ternary conditional operator. Let us take the following
-example where we read the marks data from a data file which is
-obtained as a string as we read a file. The marks can be in the range
-of 0 to 100 or 'AA' if the student is absent. In such a case to obtain
-the marks as an integer we can use the ternary conditional
-operator. Let us say the string score is stored in score_str
-variable::
-
- score_str = 'AA'
-
-Now let us use the ternary conditional operator::
-
- score = int(score_str) if score_str != 'AA' else 0
-
-This is just the if/else statement block which written in a more
-convenient form and is very helpful when we have only one statement
-for each block. This conditional statement effectively means as we
-would have exactly specified in the English language which will be
-like score is integer of score_str is score_str is not 'AA' otherwise
-it is 0. This means that we make the scores of the students who were
-absent for the exam 0.
-
-Moving on, there are certain situations where we will have to no
-operations or statements within the block of code. For example, we
-have a code where we are waiting for the keyboard input. If the user
-enters "s" as the input we would perform some operation nothing
-otherwise. In such cases "pass" statement comes very handy::
-
- a = raw_input("Enter 'c' to calculate and exit, 'd' to display the existing
- results exit and 'x' to exit and any other key to continue: ")
-
- if a == 'c':
- # Calculate the marks and exit
- elif a == 'd':
- # Display the results and exit
- elif a == 'x':
- # Exit the program
- else:
- pass
-
-In this case "pass" statement acts as a place holder for the block of
-code. It is equivalent to a null operation. It literally does
-nothing. So "pass" statement can be used as a null operation
-statement, or it can used as a place holder when the actual code
-implementation for a particular block of code is not known yet but has
-to be filled up later.
-
-{{{ Show summary slide }}}
-
-This brings us to the end of the tutorial session on conditional
-statements in Python. In this tutorial session we learnt
-
- * What are conditional statements
- * if/else statement
- * if/elif/else statement
- * Ternary conditional statement - C if X else Y
- * and the "pass" statement
-
-{{{ 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.
-Thankyou
-
-.. Author : Madhu
- Internal Reviewer 1 : [potential reviewer: Puneeth]
- Internal Reviewer 2 : [potential reviewer: Anoop]
- External Reviewer :
-