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diff --git a/conditionals/script.rst b/conditionals/script.rst index 980927f..156102b 100644 --- a/conditionals/script.rst +++ b/conditionals/script.rst @@ -1,14 +1,20 @@ .. Objectives .. ---------- -.. Clearly state the objectives of the LO (along with RBT level) +.. By the end of this tutorial, you will be able to + +.. * Use if/else blocks +.. * Use if/elif/else blocks +.. * Use the Ternary conditional statement - C if X else Y + +.. to check conditions in your programs. + .. Prerequisites .. ------------- -.. 1. Name of LO-1 -.. 2. Name of LO-2 -.. 3. Name of LO-3 +.. 1. Basic datatypes and operators + .. Author : Madhu Internal Reviewer : @@ -21,8 +27,7 @@ Script {{{ Show the slide containing the title }}} -Hello friends. Welcome to this spoken tutorial on Getting started with -strings. +Hello friends. Welcome to this spoken tutorial on Conditionals {{{ Show the slide containing the outline }}} @@ -40,10 +45,12 @@ 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:: +Python. + +For example, say, we have a variable ``a`` which stores integers and +we are required to find out whether ``a`` is even or odd. an even +number or an odd number. Let's say the value of ``a`` is 5, now. +:: a = 5 @@ -54,36 +61,29 @@ In such a case we can write the if/else block as:: 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:: +If ``a`` is divisible by 2, i.e., the result of "a modulo 2" is 0, it +prints "Even", otherwise it prints "Odd". + +Note that in such a case, only one of the two blocks gets executed +depending on whether the condition is ``True`` or ``False``. + +There is a very important sytactic element to understand here. Every +code block begins with a line that ends with a ``:``, in this example +the ``if`` and the ``else`` lines. Also, all the statements inside a +code block are intended by 4 spaces. Returning to the previous +indentation level, ends the code block. + +The if/else blocks work for a condition, which can take one of two +states. What do we do for conditions, which can take more than two +states? + +Python provides if/elif/else blocks, for such conditions. Let us take +an example. We have a variable ``a`` which holds integer values. We +need to print "positive" if ``a`` is positive, "negative" if +it is negative or "zero" if it 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 @@ -94,18 +94,18 @@ purposes of testing our code let us assume that the value of a is -3:: 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. +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. +Here too, exactly one block of code is executed -- the block of code +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 +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 @@ -124,6 +124,21 @@ elif's within an if/elif/else ladder. For example is completely valid. Note that there are multiple elif blocks and there is no else block. +Following is an exercise that you must do. + +%% %% Given a number, num. Write an if else block to print num, as is, + if it is divisible by 10, else print 10 * num. + +Please, pause the video here. Do the exercise and then continue. + +:: + + if num%10 == 0: + print num + else: + print 10*num + + 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 @@ -147,10 +162,21 @@ 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 +Following is an exercise that you must do. + +%% %% Given a number, num. Write a ternary operator to print num, as is, + if it is divisible by 10, else print 10 * num. + +Please, pause the video here. Do the exercise and then continue. + +:: + + print num if num%10 == 0 else 10*num + +Moving on, there are certain situations where we will have no +operations or statements within a block of code. For example, we have +a code where we are waiting for the keyboard input. If the user enters +"c", "d" or "x" 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 @@ -167,8 +193,7 @@ otherwise. In such cases "pass" statement comes very handy:: 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 +nothing. 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. |