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→PART 1 - Using IF Statements
:'''Perform the following steps'''
:#Open an ipython3 shell:<source lang="bash">ipython3</source>Create a temporary python file for testing things in this section.:#Let's create an if statement from the ipython3 shell.<br>Issue Try the following 2 lines, indenting the second line (you may need to press ENTER a second time for statement to execute):<source lang="python">
if True:
print('This print is apart of the if statement')
</source>What happenedwhen you ran this code? It is important to note a couple of things with the IF statement:<ul><li>When the condition in an IF statement '''evaluates to True''', it runs the code that is indented underneath it. In this case, we can use the boolean value "True" to make this happen, or test to see if a condition determined true or false.</li><li>However, if the If condition evaluates to '''False''', then it will not run the code indented underneath it. Any code not indented under the if statement will perform normally as the main program and is NOT associated with control flow statement.</li><li>Indentation means to start a line with spaces or tabs before your text. Using '''indentation''' will direct the script what code will run as part of the IF statement and which code will run as part of the main programregardless. Also, using indentation makes it easier for a programmer to identify Control Flow statements. From this point on, be VERY careful and consistent in the with indentation that you make with conditional statementsbecause it will affect how your code works. </li></ul><br>However, if the If condition evaluates to '''False''', then it will not run the code indented underneath it. Any code not indented under the if statement will perform normally as the main program and is NOT associated with control flow statement.
<blockquote style="margin-left:35px;">{{Admon/important|style="padding-left:25px"|4 spaces|While python allows some flexibility with your indentation - please don't be creative with it. Always use 4 spaces for each new block. There will be exceptions later on, but start with this now. You may find it helpful to configure your editor to insert for spaces instead of a tab when you press the tab key.}}</blockquote>
if False:
print('This first print statement will never run')
print('This second print statement will also not run')
print('This print statement will run')
</source>What do you notice?<br><br>So far, you have been using only the '''Boolean values True or False''' for your IF statements. Although this can be useful, it can be more practical to state a condition to test in order to render a '''True''' or '''False''' Boolean value to be used with control flow statements (referred to as: '''Boolean Logic''').<br><br></li>:#<li>let's create an IF statement that runs under specific conditions. Issue the following code below:<source lang="python">
password = input('Please enter a secret password')
if password == 'P@ssw0rd':
print('You have succesfully used the right password')
</source>What happened? In the above example, you are making a comparison between the value you entered via the '''input()''' function, which in turn, was saved into the '''password''' variable. The IF statement is using that variable (called password), followed by '''==''' which represents '''identical to''', followed by the string ''' 'P@ssw0rd' '''. Never use '''=''' to 'compare values since this is used to store the value into a variable and may not allow IF statement to properly test the condition! Also note that a '''space is used to separate arguments with the IF statement'''. The IF statement tests that condition to see if it is '''True or False'''. If that condition is '''True''', it will run the code indented below. On the other hand, if that condition is '''False''', it will not run the code. Try experimenting with different combinations of passwords.<br><br>If statements can also be used to compare numbers. We can do this by using comparison operators (such as: '''==''', '''!=''', '''>''', '''>=''', '''<''', '''<='''), but we can also use functions. The function '''len()''' can be used to return the number of characters in a word (plus other features). length of words and other variables. We can also use the '''len()''' function to give us the number of argumuents provided to our script by using 'len(sys.argv)' and it should return a number. Below we are also using '!='. Which stands for not eqal to. <br><br></li>:#Issue <li>Try the following lines of codeprogram:<source lang="python">
import sys
sys.exit()
</source>What happened?</li></ol>
<blockquote style="margin-left:35px;">{{Admon/important|style="padding-left:25px"|Number of Arguments with len(sys.argv)|If you are running the '''len(sys.argv)''' function in ipython3, the number of arguments returned will be always be '1'. This number will always be one higher than the actual number of arguments entered, since it also counts the script name as a argument.}}</blockquote>
