Difference between revisions of "Python/C3/Conditionals/English-timed"
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Revision as of 10:53, 21 March 2013
| Visual Cue | Narration |
|---|---|
| 0:01 | Hello friends and Welcome to the tutorial on 'Conditionals'. |
| 0:05 | At the end of this tutorial, you will be able to,
|
| 0:25 | To begin with let us start ipython, |
| 0:29 | So type ipython in the terminal |
| 0:36 | Whenever we have two possible states that can occur depending on a a certain condition, we can use if/else construct in Python. |
| 0:45 | For example, say, we have a variable a which stores integers and we are required to find out whether a is even or odd. |
| 0:52 | Let's say the value of a is 5. |
| 0:55 | So type a=5 |
| 0:59 | In such a case we can write the if/else block as |
| 1:04 | In command line if a percentage 2 == 0 colon
print in double quotes Even else colon print in double quotes Odd |
| 1:37 | If a is divisible by 2, i.e., the result of "a modulo 2" is 0, it prints "Even", otherwise it prints "Odd". |
| 1:51 | Note that in such a case, only one of the two blocks gets executed depending on whether the condition is True or False. |
| 1:58 | There is a very important syntactic element to understand here. |
| 2:03 | Every code block begins with a line that ends with a colon, in this example the if and the else lines. |
| 2:15 | Also, all the statements inside a code block are intended by 4 spaces. |
| 2:21 | Hitting enter twice, ends the code block. |
| 2:25 | The if/else blocks work for a condition, which can take one of two states. |
| 2:31 | But what do we do for conditions, which can take more than two states? |
| 2:38 | Python provides if/elif/else blocks, for such conditions. |
| 2:47 | For example. |
| 2:49 | We have a variable a which holds integer values. |
| 2:52 | We need to print "positive" if a is positive, "negative" if it is negative or "zero" if it is 0. |
| 3:04 | Let us use if/elif/else ladder for it. |
| 3:09 | For the purposes of testing our code let us assume that the value of a is -3 |
| 3:16 | Type a = -3
if a greater than 0 colon print in double quotes positive elif a less than 0 colon print in double quotes negative else colon print in double quotes zero |
| 4:17 | All the syntax and rules as said for if/else statements hold the same. |
| 4:24 | The only addition here is the elif statement which can have another condition of its own. |
| 4:30 | Here too, exactly one block of code is executed -- the block of code which first evaluates to True . |
| 4:41 | 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. |
| 4:51 | Consequently, the else block gets executed if and only if all the conditions evaluate to False. |
| 4:59 | Also, the else block in both if/else statement and if/elif/else is optional. |
| 5:08 | We can have a single if statement or just if/elif statements without having else block at all. |
| 5:17 | Also, there can be any number of elif's within an if/elif/else ladder. |
| 5:26 | For example |
| 5:28 | Type if user == in single quotes admin colon
elif user == in single quotes moderator colon elif user == in single quotes client colon |
| 5:47 | Note that there are multiple elif blocks and there is no else block. |
| 5:53 | Pause the video here, try out the following exercise and resume the video. |
| 5:57 | Given a number, num. Write an if else block to print num, as is, |
| 6:05 | if it is divisible by 10, else print 10 into num. |
| 6:12 | The solution is on your screen. |
| 6:14 | if num modulo 10 == 0 colon
print num else colon print 10 star num |
| 6:29 | In addition to these conditional statements, Python provides a very convenient ternary conditional operator. |
| 6:35 | Let us take the following example where we read the marks from a data file which is obtained as a string as we read a file. |
| 6:43 | The marks can be in the range of 0 to 100 or 'AA' if the student is absent. |
| 6:51 | In such a case, to obtain the marks as an integer, we can use the ternary conditional operator. |
| 6:58 | Let us say the string score is stored in score underscore str variable |
| 7:05 | So type score underscore str = in single quotes AA |
| 7:13 | Now let us use the ternary conditional operator |
| 7:19 | Type score = int within bracket score underscore str if score underscore str exclamation = in single quotes AA else 0 |
| 7:54 | Given a number, num. Write a ternary operator to print num, as is, |
| 8:01 | if it is divisible by 10, else print 10 star num. |
| 8:08 | The solution is on your screen. |
| 8:11 | print num if num modulo 10 == 0 else 10 star num |
| 8:19 | Moving on, there are certain situations where we will have no operations or statements within a block of code. |
| 8:27 | For example, we have a code where we are waiting for the keyboard input. |
| 8:32 | If the user enters "c", "d" or "x" as the input, we would perform some operation; nothing otherwise. |
| 8:42 | In such cases "pass" statement comes very handy |
| 8:49 | a = raw underscore input Enter 'c' to calculate and exit, 'd' to display the existing |
| 9:04 | results exit and 'x' to exit and any other key to continue |
| 9:12 | if a == in single quote c colon |
| 9:18 | elif a == in single quote d colon |
| 9:23 | elif a == in single quote x colon |
| 9:29 | else colon |
| 9:32 | pass |
| 9:35 | In this case "pass" statement acts as a place holder for the block of code. |
| 9:41 | It is equivalent to a null operation. |
| 9:45 | It literally does nothing. |
| 9:46 | 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. |
| 9:56 | This brings us to the end of the tutorial. |
| 9:59 | In this tutorial, we have learnt to, 1. Understand the conditional statements in Python. |
| 10:04 | 2. Use if/else statement. |
| 10:06 | 3. Use if/elif/else statement. |
| 10:09 | 4. Apply the ternary conditional statement - C if X else Y. |
| 10:14 | 5. Use "pass" statement. |
| 10:18 | Here are some self assessment questions for you to solve |
| 10:21 | 1. Use conditional statements for the following. |
| 10:23 | Given a variable time , print Good Morning if it is less than 12, otherwise print Hello . |
| 10:30 | 2. Convert the if else ladder below into a ternary conditional statement. |
| 10:39 | x = 20
if x greater than 10 colon print x multiply by 100 else colon print x |
| 10:48 | And now look at the answers, |
| 10:52 | 1. We can use the if/else statements as
if time less than 12 colon print in double quotes Good Morning else colon print in double quotes Hello |
| 11:06 | 1. The if else ladder can be converted to a ternary conditional statement as
print x multiply by 100 if x greater than 10 else x |
| 11:17 | Hope you have enjoyed this tutorial and found it useful. |
| 11:20 | Thank you! |
