Changes

:In previous labs, you learned some programming tools in order to make your Python scripts '''more functional''' and allowed your Python script to run differently based on different data or situations. These tools included '''objects/variables''', '''logiccondition statements''' and '''loops'''. The utilization of these basic tools not only apply to Python scripts, but basically all programming languages including interpreted (including '''Perl scripts''', '''Bash Shell scripts''', '''JavaScript''', etc ) and compiled languages (including '''C''', '''C++''', '''Java''', etc).

:In this lab, you will learn the following tools including '''functions''', '''lists''', and '''loops''', with the primary focus on creating reusable code.

:*'''Create reusable functions''' that can be imported by ipython3 or other python scripts

:*'''Looping through lists''' using '''Functions'''. Looping (iteration) is the ability for your program to repeatedly run the same code over and over. In this way, you can run a loop that contains a list to better send data to functions for better, more efficient execution of your Python script'''.

= INVESTIGATION 1: USING CREATING THE SIMPLEST FUNCTIONS =:A very simple definition of using '''functions''' is like having '''smaller programs contained inside a larger program''' that can be run by '''function name''' to perform '''repeated or commonly routine tasks'''.

:Usually, the A very simple definition of using '''functionfunctions''' will is to create and reuse '''contain programming code''' in some part of the main smaller programs within a larger program (most likely near the '''top''' of the program . In programming languages such as '''BEFOREC''' the main program). When a program is run, the '''functionC++'s code is read into internal memory''and ', ready to be run when the function is ''Java'run'', commonly used functions are pre-packaged in ' (i.e. ''libraries'function is "called"'''). By '''calling the function by name''' This relates to run dependency issues that were discussed when compiling C programming code that in your OPS235 course: if a supporting library is already stored in internal memory prevents the program from repeating the entry of repetitive codemissing, thus reducing the size of the program and making it execute more efficiently. When creating programs that define and use functions, '''a large programming task can would not be broken-down into smaller elements''' (or '''modules'''). This is why creating programs that use functions is referred able to as '''modular programming'''run the called function.

:In our situationUsually, a Python '''function''' is will '''contain programming code''' in some part of the python file (most likely near the top of the file, before the main program). We refer to that as a '''predefined set of code"function declaration"'''.: When a program is run, this the '''function's code is loaded read into python (eg. internal memory''', ready to be run when the function is executed (referred to as '''calling the function'''), but it does not immediately perform any actions. Functions may accept arguments and/or return values, or not accept arguments and/or return values. Until a Function is specifically told to execute, it's its code will sit (in internal memory) unused.

 :#To start, open ipython and try experimenting with functionsCreate a new python file for testing code in this section.<source>ipython3</source>:#Whenever you want to create a function, you must start with the keyword "'''def'''". The '''def''' keyword is used to start the definition of the function, it does not run the code you write. Functions, just like '''if ''' statements, must have all code under them indented.<sourcelang="python">

:#Executing your file you should have noticed that nothing happened. Well actually, something did happen... the function called '''hello(''') has been defined and stored in internal memory in order for it to run when called by its function name. Now that our function is was created , we can use it over and over. :#To execute the code inside the function, run the function name with "'''()'''" '''brackets''' at the end of the function name.<br>Try running the '''hello()''' function by name three times like this:<sourcelang="python">

</source>You should notice that the function just does the same thing over-and-over no matter how many times your call the function by name. By the way, that is OK. On the other hand, you may want to create and use a function to do something, like perform error checking or some other task that returns a value to the '''main''' program for further processing. For example, a '''true''' or '''false''' value if the error checking function that was called was detected no errors or detected an error. But let's stick to some simple examples first, before tackling more complex use of functions.<br><br>:#Next, Let's create a function that '''returns ''' some data after the function runsis called. This function does not print out any text, : instead; it creates new variables and at the end returns the valueof one of the variables.<sourcelang="python">

:#The different Call the function like this:<source lang="python">return_text_value()</source>One major difference between a function '''returning a value ''' and simply '''printing a value, ''' is that '''returned ''' values can be caught and stored in variables used in the program (that called the function) for later use. Once the returned value has been stored, it can be printed, manipulated, compared in if IF statements, and moreetc. Below will cover how to store a returned value.<br><br>:#Notice that this syntax looks just the call to the input() function which you've used in the last lab:<sourcelang="python">

:#Now the returned text from the function has been stored in the variable "'''text'''". It can be used like any string value now.<sourcelang="python">

'''Functions and Numbers (Integers)''' : You will now learn how to define and run functions that will return '''integer data''' when a function is called. In this section, you will define a function that will be returning integer values instead of text. There is not a big difference, but when returning number values, care needs to be taken if you try combining it with a string! 

:#In this next example Define the functions will be returning integer values instead of text. There is not a big difference, but when returning number values, care needs to be taken if you try combining it with a string.return_number_value() function:<sourcelang="python">

:#Now try storing the return value of the above function.And call it:<sourcelang="python">

</source> What do you notice?<br><br>:#The warning again, because this is a number valueNow, using it with display both strings can cause errors. and numbers:<sourcelang="python">

---------------------------------------------------------------------------</source> What do you notice? You should notice a warning message. This occurs because the returning value is a '''number''' and NOT a '''string'''! Combining numbers and strings in a statement (such as '''print()''') can cause errors. The error message should appear similar to the one displayed below: <source>TypeError Traceback (most recent call last):<ipython-input-24-d80d5924146a> File "test.py", line 2, in <module>()----> 1 print('my numbr number is ' + number) TypeError: Cancannot concatenate 't convert str' and 'int' object to str implicitlyobjects

:#If a number needs to be combined with a string , use the one of '''str()''' predefined function that was discussed in a previous lab in order to convert the following syntax below.returned number into a string:<sourcelang="python">

# Function returning == PART 2 - Creating a Python Script with Functions and Importing Functions == '''Creating a Python Script''' :Now it's time to create a Python script that uses two functions. One function returns a string valuedef return_text_valueto greet the user, where the other function returns the result of adding two values (stored in variables within the function). :'''Perform the following Instructions:'''  name = :#Create a new script '''Terry~/ops435/lab3/lab3a.py' return 'Good Morning ' + name

# Function returning integer valuedef return_number_value(): num1 = 5 num2 = 10 num3 = num1 + num2 return num3::'''Input / Output Requirements'''

:::*The script should have a '''Shebang line''':::*Below the '''Shebang line''', add an '''empty line''' followed by a comment stating: '''# This IF Statement may seem cryptic and unclearreturn_text_value() function''':::*Add an '''empty line''' followed by the '''return_text_value()''' function '''definition''' that you previously entered in the shell. Any code written under this if statement will be run when :::*Add another '''empty line''' followed by a comment stating: '''# return_number_value() function''':::*Add another '''empty line''' following by the '''return_number_value()''' function '''definition''' that you run your scriptpreviously entered in the shell. :::*Add a '''couple of empty lines''', following by a comment stating: '''# Main Program''':::*Add another '''couple of empty lines''', followed by the statements displayed below:<source lang="python">

:Running your program you should have seen three lines being displayed: the text "python code", a greeting, and a result of a math calculation. The '''if''' statement in the code above is a special '''if''' statement needed to make sure that your "main" code only runs when you want it to. More on that later. '''Importing Functions From other Python Scripts''' In order to use functions from other scripts, you use the '''import''' statement.<br><br> :# Let's see what happens if we forget to import functions from your lab3a.py script prior to calling a function. Create a new python file and try to call the return_text_value() function:<source lang="python">text = lab3a.return_text_value()</source>You should notice an error indicating '''"name 'lab3a' is not defined"'''. This error occurs since you failed to instruct python to '''import''' or "load existing defined functions from your lab3a.py script" to '''internal memory'''.<br><br>:#Exit Modify your program like this:<source lang="python">import lab3atext = lab3a.return_text_value()print(text)lab3a.return_number_value()</source> You should notice that all of the ipython3 shell, download function calls should now work.:# Download the checking script and check your work. Enter the following commands from the bash shell.<sourcelang="bash">

ls CheckLab3.py || wget matrix.senecachttps://raw.ongithubusercontent.cacom/~acoatleySeneca-willisCDOT/ops435/master/LabCheckScripts/CheckLab3.py

:#Before proceeding, make certain that you identify any and all errors in lab3a.py. When the check checking script tells you everything is ok OK before proceeding to the next step.:#Start up ipython3 shell again.<sourcebr>ipython3</sourcebr> = INVESTIGATION 2:#The if statement line found in lab3a.py is special if statement. It allows scripts to be imported into other python environment while only defining the functions, this powerful feature allows for python scripts to run differently depending on if you run it or import it. Take a look at the code, there is NO reason to run this in ipython3.<source>CREATING FUNCTIONS WITH ARGUMENTS AND RETURN VALUES = if __name__ == PART 1 - Providing Functions With Arguments == :Functions can receive '''__main__arguments': print('python code')</source>:#To show examples of how the above if statement works- data to be used for processing. In this section, run the lab3a.py script. The output will show that all the code found under the if statement was run. <source>run lab3a.py</source>:#This next example will show when the code under the if statement does NOT run.<source>import lab3a</source>:#When you import a python script it will run all code found that is not indented, including defining all of the learn how to define functions. But, when importing, python will not run any code under the special if statement. Now that the script has been imported, we can run accept arguments and learn how to call functions previously written.<source>text = lab3a.return_text_valuewith arguments (such as mathematical operations or testing conditions, which is useful for error-checking)textlab3a.return_number_value()</source>

== PART 2 - Providing Functions With '''Passing up Single and Multiple Arguments ==Functions can take arguments that work similarly to Python scripts. In this section, the functions created will be given arguments, these functions will use the given arguments to provide different output.a Function'''

:#Start Create a new Python file for testing.:#When passing arguments to functions, you put data such as '''strings''', '''numbers''', or '''variable names''' within brackets immediately following the ipython3 shellfunction name.<sourcebr>ipython3</sourcebr>'''NOTE:#To create ''' If a new function that accepts arguments, provide then those arguments must be declared (using variable names) when the function is declared. Those declared variable names in are then used within the functions bracketsfunction for processing. But if Also, when you call a function is given with arguments, the number of arguments in passed up to the definition, it function must always get match the same number of arguments when you call that were specified in the functiondeclaration.<br><br>:#Define a function called '''square()''':<sourcelang="python">

</source>'''FYI:#To square a number in math your multiply using '''You may have learned that you multiple a number * by itself in order to "square" the number. In python, the ''' or use exponents '''number ** 2''' operator will raise the operand on the left to the power of twothe operand on the right. This function takes one argument <br><br>When calling functions with multiple arguments, the arguments are separated by '''numbercommas'''. See what happens if you provide strings, strings without using quotes, or numbers with decimals in the following examples.:#Test your '''square()''' function will use exponents to multiply the number given by itself.:<sourcelang="python">

square('2')</source>Notice that nothing is printed, you need to print the values the functions return to see what they are.:#Providing more than one argument in The last function call should produce an '''error message'''. This is caused by sending a '''string''' instead of a number that is processed by the function requires . We could use the use of commas. Be careful NOT int() function to provide strings or decimals, convert any value passed in as you may cause errorsa string by mistake to an integer number.<br><br>:#Declare the function '''sum_numbers()''':<sourcelang="python">

:#Running functions with multiple arguments is the same. When you put a Call that function as a argument of another function, the inner-most function will run first, and the return value will be used as the argument on the outer function. For example, in this case below, '''sum_numbers(5, 5)''' will return '''10''', and provide square with that value '''square( 10 )'''.to see what happens:<sourcelang="python">

</source>'''NOTE:''' Running functions with multiple arguments is the same. When call a function as an argument of another function, the '''inner-most function will run first''', and the return the value from that will be used as the argument for the '''outer function'''. In the example below, '''sum_numbers(5, 5)''' will return '''10''', thus providing that result to be square with that value '''square(10)'''.<br><br> '''Practice Creating a Function that Accepts Arguments and Returns a Value''' :It is time to practice creating a shell script that uses a function that accepts arguments, and returns a value.

:#The next script is NOT COMPLETE, your job is to make the script do what it askes. It contains 3 functions, one of adding, one for subtracting, and one for multiplying. Make sure each function performs the correct operation and returns a integer value. Create a new script '''~/ops435/lab3/lab3b.py''' with . Refer to the following contents'''Python Script template''' and the '''Additional Requirements''' sections when creating your Python script. Refer to Sample Run and Sample Imports displayed below for exact prompt and output  :::'''Python Script Template''' :::<sourcelang="python">#!/usr/bin/env python3

def subtract_numbers(number1, number2):

def multiply_numbers(number1, number2):

 :::*The script should have a '''Shebang lineAdditional Requirements''':::*The script should have a function sum_numbers(number1, number2):::*The script should have a function subtract_numbers(number1, number2):::*The script should have a function multiply_numbers(number1, number2):::*All functions should accept two arguments:::*All functions should return a an integer:::*The script should contain no errors :::2. '''Sample Run 1:'''<sourcelang="python">run ./lab3b.py

::'''Other examples:3. Sample Import 1:'''<sourcelang="python">ipython3 

lab3b.sum_numbers(10, 5)# Will return 15lab3b.sum_numbers(25, 25)# Will return 50lab3b.subtract_numbers(10, 5)# Will return 5lab3b.subtract_numbers(5, 10)# Will return -5lab3b.multiply_numbers(10, 5)# Will return 50lab3b.multiply_numbers(10, 2)# Will return 20</source>

sum_numbers(25, 25)50 subtract_numbers(10, 5)5 subtract_numbers(5, 10)-5 multiply_numbers(10, 5)50 multiply_numbers(10, 2)20</source>:::42. Exit the ipython3 shell, download Download the checking script and check your work. Enter the following commands from the bash shell.<sourcelang="bash">

ls CheckLab3.py || wget matrix.senecachttps://raw.ongithubusercontent.cacom/~acoatleySeneca-willisCDOT/ops435/master/LabCheckScripts/CheckLab3.py

'''Multiple Arguments ::3. Before proceeding, make certain that you identify any and IF Statements'''all errors in lab3b.py. When the checking script tells you everything is OK - proceed to the next step.

The next '''Passing up Multiple Arguments and Using Conditional Statements''' :You will now create a more complex function we make in this section if going that will not only pass arguments, but also include logic to control the flow of the function, and affect how your Python script will be more advanced and contain logic inside itrun. First try the following to practice logic in functionsYou will create a function that uses an '''if/elif/else''' statement.

:#Start the ipython3 shell<source>ipython3</source>:#Now try making some functions that uses if statements, '''BUT BEWARE''', making an if statement inside Use a function means that you are indented two times to get temporary Python file to define the if statement.following function:<sourcelang="python">def check_temperaturedescribe_temperature(temp):

return 'ok' </source>The final '''return "ok"''' will only take place if a previous return has not taken place before it. Once return has been used in a function, the function immediately exits and returns the value.:#Call describe_temperature like this to confirm the results:<source>print(describe_temperature(50))# Will return 'hot'print(describe_temperature(20))# Will return 'perfect'print(describe_temperature(-50))# Will return 'cold'print(describe_temperature(25))# Will return 'ok'print(describe_temperature(10))# Will return 'ok'

check_temperature(-50)'cold''Create a Python Script Receiving Multiple Arguments'''

:#Create the '''~/ops435/lab3/lab3c.py''' script. The purpose of the script is to make have a single function that can perform addition, subtraction, or multiplication on a pair of numbers. But the function will allow us to choose exatly what operation we are performing on it when we call the functionit. If the operate function does NOT understand the operator given, it should return a an error message(e.g. calling the function to 'divide' two numbers).:#Use this template to get started:<sourcelang="python">

:::*The script operate() function should have a use '''conditional'Shebang line''statements<br> &nbsp; '''FYI:::*The script should have a function operate''' Remember that you MUST consistently '''indent ALL code''' for within each section (num1, num2, operatoror test):::*The script should use if statements inside the operate function.:::*The operate () function should accept '''three arguments'''.:::*The operate () function should '''return ''' the answerresult.:::*The operate () function should '''return a ''' an error message if the operation is unknown<br> &nbsp; '''FYI:''' Use single quotes or double-quotes to pass a string value.:::*The script should contain show the exact output as the sample imports.:::*The script should contain no errors.:::3*As an extra exercise, try to write your function with only one return statement.  :::'''Sample Run 1:'''<source>run ./lab3c.py

 :::4. '''Sample Import 1Run 2 (using import from another Python file):'''<source>

 lab3c.operate(10, 20, 'add')# Will return 30 lab3c.operate(2, 3, 'add')# Will return 5 lab3c.operate(100, 5, 'subtract')# Will return 95 lab3c.operate(10, 20, 'subtract')# Will return -10 lab3c.operate(5, 5, 'multiply')# Will return 25 lab3c.operate(10, 100, 'multiply')# Will return 1000 lab3c.operate(100, 5, 'divide')# Will return Error: function operator can be "add", "subtract", or "multiply" lab3c.operate(100, 5, 'power')# Will return Error: function operator can be "add", "subtract", or "multiply"

:::53. Exit the ipython3 shell, download Download the checking script and check your work. Enter the following commands from the bash shell.<sourcelang="bash">

ls CheckLab3.py || wget matrix.senecachttps://raw.ongithubusercontent.cacom/~acoatleySeneca-willisCDOT/ops435/master/LabCheckScripts/CheckLab3.py

:::64. Before proceeding, make certain that you identify any and all errors in lab3c.py. When the check checking script tells you everything is ok before proceeding OK - proceed to the next step.<br><br>

== PART 3 2 - Running System Commands with Subprocess ==This last part :The remainder of the this investigation will give allow you access to run operating system commands within via your python scriptsPython script. While we Although there are able to run some bash commands inside the ipython3 environment, these do not transfer over into the python code we write. It is not usually a good idea different ways in which to run system commands in Python, this makes your Python code less portable and makes it require a speicifc issue operating system or a system that has those commands available. There is also the case of security, allowing python to execute commands on the system can be a security problem if care isn't taken. For these reason you should only use subprocess and the system commands as a last resort and stick to Python code onlywill learn two of them.

:#Start Create a new python file for testing.:#Import the ipython3 shell'''''os''''' module in your python file.:#You can issue operating system commands by using the '''system()''' function. Try it:<sourcelang="python">import subprocessos.system('ls')os.system('whoami')diros.system(subprocess'ifconfig')</source>Notice that the output from the programs is printed in your script. Consider that may not always be what you want.<br><br>:#Try this also:<source lang="python">os.system('ipconfig')</source>You should notice an error message: ''''ipconfig: command not found''''. That error occurs since that command was an MS Windows command, and our current platform is Linux.<br><br>It is not always a good idea to run system commands in Python, this makes your Python code less portable and makes it require a specific operating system or a system that has those commands available. You should think about that when you decide whether you should or should not use a system command to accomplish some task or stick to pure Python code only.<br><br>As you may recall from lab2, you issued '''import sys''' to import special variables from the system. You can import a subprocess in order to run common non OS specific commands securely.<br><br>:#Import the subprocess module in your python file.:#There are many available modules and attributes features available as part of the subprocessmodule, we are interested in "'''Popen'''". This method subprocess.Popen() can be used to run system commands as a child process to the Python script. This The code below output will create a new child process, in Python we can control this through the new Python object we just created, "'''p'''". "'''p'''" now has a collection of methods(functions that are apart of a object) available.<br><br>:#To demonstrate, view them with '''dir()'''.issue the following:<sourcelang="python">

dir(p)</source>This function call and the following step is full of details we haven't yet talked about which is why it may look a little scary. By the time we're finished with the course - you will be able to look at code like this and not be intimidated. If you're curious and want to look ahead - you can find the definition for the [https://docs.python.org/3/library/subprocess.html#subprocess.Popen Popen function in the Python reference manual].:#This next step is going to communicate with the process and get the retrieve it's output (stdout and stderr from the command we previously).<source>stdout, stderr output = p.communicate()stdoutprint(output)print(output[0])

stdout = stdoutoutput[0].decode('utf-8').strip()print(stdout)

:#While many of these system commands could Sometimes you will be instead written in simply Pythonable to use purely python code to get your job done, the exercise of running but often you will need to call existing system commands is . It's importantto learn how to call them and how to interact with those external processes.

:#<ol><li>Create the "'''~/ops435/lab3/lab3d.py'''" script. The purpose of this script is to create a Python function that can return the linux system's root directory free space.:::*The script should have a '''Shebang lineimport the correct module''':::*The script should import subprocess:::*The script should use the linux command ": '''<nowiki>df -h | grep '/$' | awk '{print $4}'" </nowiki>''' :::*The script should contain the function called: '''free_space()''':::*The function '''free_space() ''' should return a string which is in '''utf-8 ''' and has '''newline characters striptstrip''':::*'''Note: ''' your output may be completely different, the free/available disk space on every computers root directory may be different.:::2. '''Sample Run 1: ''' <source>run ./lab3d.py

:::3. '''Sample Import 1Run 2 (using import from another Python file):'''<source>

'# Will return 9.6G'</source></li>:::4. Exit the ipython3 shell, download <li>Download the checking script and check your work. Enter the following commands from the bash shell.<sourcelang="bash">

ls CheckLab3.py || wget matrix.senecachttps://raw.ongithubusercontent.cacom/~acoatleySeneca-willisCDOT/ops435/master/LabCheckScripts/CheckLab3.py

</source></li>:::5. <li>Before proceeding, make certain that you identify any and all errors in lab3d.py. When the check checking script tells you everything is ok before proceeding OK - proceed to the next step.</li></ol>

= INVESTIGATION 2 - 3: USING LISTS =Lists are ones of the most powerful data-types in Python. A list is a series of comma separated values found between square brackets. Values in a list can be anything: strings, integers, objects, even other lists. In this section we will introduce lists and how to use them effectively, we will come back to lists again in later labs.

:#Start the ipython3 shell<source>ipython3</source>Create a new Python file for testing things in this section.:#Create a few lists with different values: list1 contains only '''integers''', list2 contains only '''strings''', list3 contains a combination of both.'''integers and strings''':#<sourcelang="python">

:#The best way to get individual You can also retrieve ranges of items from a list is using the list index. The index is a number starting from 0 to (number_of_items - 1these are called slices), the index starts counting at 0.<source>list1[0] # First item in list1list2[1] # Second item in list2list3[-1] # Last item in list3</source>:#Instead of just getting the first and last, lists can give ranges of items. <sourcelang="python">print(list1[0:5] ) # Starting with index 0 and stopping before index 5print(list2[2:4] ) # Starting with index 2 and stopping before index 4print(list3[3:] ) # Starting with index 3 and going to the end</source>:#Lists can also contain other lists. This means lists can contain: lists and strings and integers all together. <source>list4 = [ [1, 2, 3, 4], ['a', 'b', 'c', 'd'], [ 5, 6, 'e', 'f' ] ]</source>:#This list still only has 3 index locations. Each index points to another list. <source>list4[0]list4[1]list4[2]</source>:#To access a list inside another list, a second index is needed. Spend some time trying out the syntax and try and navigate to a specific spot in the list.<source>list4[0][0] # First item in first listlist4[0][-1] # Last item in first listlist4[2][0:2] # First two items in third list</source>:#Using different items from different lists to create new lists.<source>first_only_list = [ list1[0], list2[0], list3[0] ]first_only_list

:# Put Create a Python script called: '''~/ops435/lab3/lab3e.py'''<br>The purpose of this script is to have a number of functions that output a different data storage in various elements of a list. Each function will return either a single item from the list OR will create a new list and return the entire new list .<br><br>:#The template function names and the special if statement:<source lang="python">#!/usr/bin/env python3 # Create the list called "my_list" here, not within any function defined below.# That makes it a global variable. We'll talk about that in another lab.

# Does not accept any arguments # Returns all of the entire list global variable my_list unchanged

# Does not accept any arguments # Returns a single string that is the first item in the listglobal my_list

# Does not accept any arguments # Returns the a list that includes the first and last items in the listglobal my_list

# Does not accept any arguments # Returns the a list that includes the second and third items in the listglobal my_list

if __name__ == '__main__': # This section also referred to as a "main code"

 :::*The script should have a '''Shebang lineAdditional Requirements''' :::*The script should have declare a list called '''my_list''' created BEFORE any function definition:::*The list called '''my_list ''' should have the values: '''100''', '''200''', '''300''', and ''''six hundred'''':::*The script should '''implement''' the empty functions - i.e. you have a function called give_list() which returns a listto fill in the bodies for these functions:::*The script should have a function called give_first_item() which returns a string:::*The script should have a function called give_first_and_last_item() which returns a list:::*The script should have a function called give_second_and_third_item() which returns a list:::3. '''Sample Run 1:'''<source>run ./ lab3e.py

:::4. '''Sample Import 1Run 2 (with import from another script):'''<source>

# Will print [100, 200, 300, 'six hundred'] 

# Will print 100 

# Will print [100, 'six hundred'] 

# Will print [200, 300] 

:::53. Exit the ipython3 shell, download Download the checking script and check your work. Enter the following commands from the bash shell.<source>

ls CheckLab3.py || wget matrix.senecachttps://raw.ongithubusercontent.cacom/~acoatleySeneca-willisCDOT/ops435/master/LabCheckScripts/CheckLab3.py

:::64. Before proceeding, make certain that you identify any and all errors in lab3e.py. When the check checking script tells you everything is ok before proceeding OK - proceed to the next step.

 :There are a number of ways to get obtain information about lists, as well as change what the data that is inside contained within a list. This In this section , you will cover the different ways learn how to manipulate lists.

 :#First start with the smallest Let's perform a simple change. Change a single item at a single point in to a listelement.Try the following code:<sourcelang="python">

print(courses[0])

print(courses[0])print(courses)

:#Now lets use the dir() and help() Below are some examples of using built-in functions to see what functions and attributes '''manipulate''' lists have. The help() Take your time to see how each function will also give us tips on how to use some functions.<source>dir(courses)help(courses)</source>:#Next search and find more information on can be a number list functions useful tool for changing making changes to existing lists.:<sourcelang="python">help(courses.append)

print(courses)

print(courses)

print(courses)

help(courses.sort)sorted_list sorted_courses = courses.copy() # Create a copy of the courses listsorted_listsorted_courses.sort() # Sort the new listprint(courses)print(sorted_courses)

:#Using Python In addition to using functions we can get more to manipulate lists, there are functions that are useful to provide '''information out ''' regarding the list such as number of lists.elements in a list, the smallest value and largest value in a list:<sourcelang="python">

length_of_list = len(list_of_numbers) # Returns the length of the listsmallest_in_list = min(list_of_numbers) # Returns the smallest value in the listlargest_in_list = max(list_of_numbers) # Returns the largest value in the list</source>:#Now Notice how the long line below is wrapped to fit on to some of the more powerful features of Python lists. Searching for values inside lists and finding locations of values in a list. The index() function allows searching inside a list for a value, it will return the index number of the first occurence. <source>one screen:number = 10helpprint(list_of_numbers.index)list_of_numbers.index"List length is " + str(numberlength_of_list) # Return index of the number searched for+ </source>:#The problem that comes up here is if the item searched for doesn't exist ", Python will throw a error. Lets make sure it exists before asking for smallest element in the index location. To find out if a value is in a list, just ask using a if statement, if the statement is True" + str(smallest_in_list) + ", then the value is found largest element in the list.<source>list_of_numbers = [ 1, 5, 2, 6, 8, 5, 10, 2 ]number = 10if number in list_of_numbers: # Returns True if value in list, returns False if item not in list number_index = list_of_numbers.index(number)else: # If the statement is False, the else will run print(" + str(numberlargest_in_list)) + ' is not in list_of_numbers'

:This final last section explains demonstrates an extremely useful for lists: the best part about lists. The ability to quickly '''loop through every value in the list'''. '''For loops''' have a set number of times they loop. The '''for loop''' loop will one by one run execute all indented code for each item (element) in the list.

:#:The following '''for loop''' loop will create a new variable that contains store the value of each element from list_of_numbers within a variable named '''item''' and run code indented below the list of the current iterationloop for each item.<br><br>:#Run this from a temporary Python file:<sourcelang="python">

:#Now As you can see: instead of running functions over and over, from our previous sectionswriting eight function calls for each element of the list, we can put them call the function in a loop. The next sequence And we won't have to rewrite code if the length of code will apply a function to every item in the listchanges.<br><br>:#Run the following code:<sourcelang="python">

print(square(value))

</source>:#But this The code above only prints out each new valuethe squares and does not save them for future use. Lets try making The next example uses a new function that loops through listslist, squares the values, and returns also saves the squares in a new list.<br><br>:#Run the following code:<sourcelang="python">

print(list_of_numbers)print(new_list_of_numbers)</source>:#The above is just one example of a quick, powerful, use of for loops mixed with lists. But be careful when passing lists into functions. When you give a function a listas an argument, it is the actual list reference and NOT a copy. This means a function can completely change the list without making a new list. While you do have to be careful , this is can also be useful, a . A function can modify any given list, ''without '' have to return or store it.<br><br>:#To demonstrate, run the following code:<sourcelang="python">

print(list_of_numbers)

def add_item_to_list(my_list): # Appends new item Create the '''~/ops435/lab3/lab3f.py''' script. The purpose of this script is to end of use functions to modify items inside a list which is . <source lang="python">#!/usr/bin/env python3 # Place my_list below this comment (before the (last item + 1function definitions)  

def add_item_to_list(ordered_list): # Appends new item to end of list with the value (last item + 1) def remove_items_from_list(my_listordered_list, items_to_remove):

:::*The missing list should have the values: '''1, 2, 3, 4, 5''':::*The program should have a function called '''add_item_to_list(ordered_list)'''<dd><dl>This function takes a single argument which is a list name itself. It will then look at the value of the last existing item in the list, it will then append a new value that is one unit bigger (i.e. '''+1''' and modifying that same list without returning any value).</dl></dd>:::*The script should have a function called '''remove_items_from_list(ordered_list, items_to_remove)'''<dd><dl>This function takes two arguments: a list, and a list of numbers to remove from the list. This function will then check if those items exist within that list, and if they exist, then they will be removed. This function will modify the list without returning any value.</dl></sourcedd>

:::*The script should have a '''Shebang line''':::*The list '''my_list''' should have the valuesSample Run 1: '''1, 2, 3, 4, 5''':::*The script should have a function called add_item_to_list(my_list) :::*The script should have a function called remove_items_from_list(my_list, items_to_remove) :::*The function add_item_to_list(my_list) takes a single argument which is a list. This function will look at the value of the last item in the list, it will then append a new value that is +1 bigger then the previous number. This function modifies the list without returning any value:::*The function remove_items_from_list(my_list, list_of_numbers_to_remove) takes two arguments, a list, and a list of numbers to remove from the list. This function will then check if those items are in the list, if they are it will remove them. This function modifies the list without returning any value.:::2. Sample Run 1:<source>

 print(my_list)# Will print [1, 2, 3, 4, 5, 6, 7, 8] 

 print(my_list)# Will print [2, 3, 4, 7, 8]

:::42. Exit the ipython3 shell, download Download the checking script and check your work. Enter the following commands from the bash shell.<source>

ls CheckLab3.py || wget matrix.senecachttps://raw.ongithubusercontent.cacom/~acoatleySeneca-willisCDOT/ops435/master/LabCheckScripts/CheckLab3.py

:::53. Before proceeding, make certain that you identify any and all errors in lab3f.py. When the check checking script tells you everything is ok before proceeding OK - proceed to the next step.

 ::<span style="color:green;font-size:1.5em;">&#x2713;</span> Lab3 logbook notes completed'''Be able to answer any questions about the lab to show that you understood it!'''

= Practice For QuizzesLAB REVIEW = :# What is the purpose of using functions in a Python script?:# Write Python code to define a function called '''greetings()''' that when called will greet the user by name and on the next line display the current date:# Why is it useful for functions to accept '''arguments''' passed-up upon function execution?:# What is the purpose of the '''import''' command? What can be the consequence if the import command is not used prior to running a function by name?:# Write Python code to define a function called '''join()''' that excepts two arguments which will be be stored as the variables called '''word1''' and '''word2''' respectively during the execution of the function.:# What is the command to return a value from a function?:# What is the purpose of the '''system()''' function?:# What is the purpose of a '''list'''?:# Assume that the following list has been defined: '''mylist = [ 'apple', 1, 'grape', 2, 'banana', 3, ]'''<br>Based on that, what will the following contain?<source lang="python">mylist[0]mylist[3]mylist[-1]mylist[0:1]</source>:# Assume that the following list has been defined: '''combined_list = [ [7, 5], ['x', 'y'], [ 5, 'f' ] ]'''<br>Based on that, what will the following contain?<source lang="python">combined_list[0]combined_list[1]combined_list[1][0]combined_list[2][0:2]</source>:# Briefly explain the purpose of each of the following functions (methods) that can be used with lists: '''append''', '''insert''', '''remove''', Tests'''sort''', Midterm &amp; Final Exam '''copy'''.</li>:# Write the '''functions''' that perform the following operations on a list:<ol type="a"><li>Returns the length of the list</li><li>Returns the smallest value in the list</li><li>Returns the largest value in the list</li></ol>:# Write a Python script to display all of the elements within a simple list.

[[Category:# x:# x:# xOPS435-Python]]