OPS435 Online Lab1

Introduction to git, github.com, and Python

Lab Objectives

• Using the "git clone" command to clone a repository into a new directory
• Set up account on github.com for creating, tracking, and managing a repository
• configure and explore the Python interpreter on matrix.senecacollege.ca

Overview

In this lab, you will create an account on github.com and follow the Github "Hello World guide" to create a new public repository on github to and explore the basic workflow of using github to track and manage revisions of software or other contents. The essential operations provided by Github includes

• creating new repository,
• creating a new branch,
• making changes to files,
• creating a pull request, and
• opening and merging a pull request.

You will then use the git client (git clone) on matrix.senecacollege.ca to access and download the contents of the repository you created on github. Note: if you have your own Linux VM ready, you can also install and use the git client on your VM.

You will also use the git client on matrix.senecacollege.ca to clone the repository on github.com which hosts the Python scripts for lab 1.

Study and execute the Python scripts downloaded from the lab 1 repository

Reference

• Github git Cheat sheet
• Github Hello World Guide

Glossary

• git - a distributed revision control system with rich command set that provides both high-level operations and full access to git's internals.
• github.com - a code hosting platform for version control and collaboration that lets people work together on software projects from anywhere.

Unit Feedback Script : CheckLabX.py

Unit Feedback Scripts
Each Part (within an 'Investigation) is referred to as a Unit. Each Unit will require that the student download and run a Unit Feedback Script, which provides the OPS435 student "real-time feedback" of their completed work.
This feedback is not considered to be perfect or fool-proof; however, it may provide feedback (hints) in case a student gets stuck or experiences an error when performing administration tasks or when creating their Python scripts. These unit feedback scripts can also be used to confirm that the student's Python script is on the right track, and provide a consistent record of their Python scripting progress throughout their labs.

Investigation 1 - git and github.com

Task 1: Create a Github.com account

• Start your web browser and go to github.com and use your own email to sign up for a new github account if you don't already have one.
  [Note: Please be aware that Seneca's spam filter block email from github.com by default, if you use your Seneca email to sign up for an account on github.com, you might have to re-configure your email spam filter to allow confirmation email from github.com to reach your inbox.]
• Record your github.com user name on your lab logbook.
• email your github.com user name to your OPS435 professor from your Seneca email account.

Task 2: Create a project and make a pull request on GitHub

Follow the Github "Hello World Guid" here to perform the following activities:

• Create a repository
• Create a branch
• Make and commit changes
• Open a pull request, and
• Merge your pull request

Please make the following changes when following the guide:

• name the new repository using your Seneca user name instead of "hello-world".
• add your full name, and OPS435 section to the README file, do not post any other personal information there.

Task 3: Clone a Github.com repository into a new directory on a Linux system

You can do the following steps either on matrix.senecacollege.ca or on your CentOS 7 vm:

• login to matrix.senecacollege.ca or your CentOS 7 vm
• create a directory named ops435/lab1 under your home directory
• change your working directory to ~/ops435/lab1
• run the following git command to clone the repository you created in Task 2 on github.com

   git clone https://github.com/[your_github_user_name]/[your_seneca_user_name]

for example, if your github user name is rc2030, and your seneca user name is rchan, the git command to clone the repository you created in Task 2 should be:

   git clone https://github.com/rc2030/rchan

• change your working directory to your cloned git repository, which should be ~/ops435/lab1/[your_seneca_user_name]
• run the following two commands and capture their output to the named files:

   git log > gitlog.txt

   tree -a > repo_tree.txt

• Make sure that gitlog.txt and repo_tree.txt are not empty. Review and study the contents of gitlog.txt and repo_tree.txt

Investigation 2 - Python on Matrix

A few background information about the Python programming language

• The Python Interpreter understanding the Python language and this is why we are going to learn this programming language in this course.
• The Python Language supports both object-oriented programming and procedural programming paradigms.
• The Python programming environment consists of a few basic components: language keywords, symbols, modules, and data objects.
• The Python Interpreter supports two mode of operations: script mode and interactive mode.
• In interactive mode, the Python interpreter allows us to run python code one statement at a time. Currently, there are two major versions of the Python interpreter available on matrix.senecacollege.ca: version 2 and version3.
• To start an interactive Python version 2 shell, type "python" at the command prompt.
• To start an interactive Python version 3 shell, type "python3" at the command prompt.

Part I - Python Versions on Matrix

• You can access the Python Interpreter on Matrix from a Linux machine or a Windows 10 machine.

Login to matrix.senecacollege.ca from a CentOS 7 machine

• To login to matrix.senecacollege.ca must must have a active Seneca user account.
• The following is a screen shot showing the login from a CentOS Linux (host or vm) system with an active Seneca user name:
  
  

Login to matrix.senecacollege.ca from a Windows 10 machine

• Login to matrix.senecacollege.ca with your Seneca user name from Windows 10's run box.
  
  

Identify and explore Python versions on Matrix

• Once you are on matrix.senecacollege.ca, run the python command to start a Python version 2 interactive shell at the command prompt. The last line displayed should be >>>. the >>> sign is referred to as the Python interactive shell prompt.
  • python
  • at the >>> prompt, type help('keywords') and record the output
  • at the >>> prompt, type help('symbols') and record the output
  • type exit() at the >>> prompt to exit from the Python interactive shell.
• Run the python3 command to start a Python version 3 interactive shell session at the command prompt.
  • python3
  • at the >>> prompt, type help('keywords') and record the output
  • at the >>> prompt, type help('symbols') and record the output
  • type exit() at the ">>>" prompt to exit from the Python interactive shell.

• Compare the list of keywords and symbols for Python version 2 and version 3. Which keyword(s) is/are remove from version 2 in version 3?

Part II - Create directory structure for Labs and Assignments

Create directory structure using BASH commands

• Lets setup and reserve the following directories for storing and organizing files for labs and assignments. Execute the following commands at the command prompt:

  mkdir ~/ops435/lab2
  mkdir ~/ops435/lab3
  mkdir ~/ops435/lab4
  mkdir ~/ops435/lab5
  mkdir ~/ops435/lab6
  mkdir ~/ops435/lab7
  mkdir ~/ops435/lab8
  mkdir ~/ops435/a1
  mkdir ~/ops435/a2

Verify the directory structure created

• Download the sample.py script from https://github.com/rayfreeping/ops435-lab1 repository to ~/ops435/lab1 directory
• Study and Explore the sample.py python script and identify the following sections:
  • the shebang line
  • the script level doctstring
  • the import section to import functions from the standard library module
  • the function definition section
  • the main script section
• Also identify the following items appear in the sample.py script:
  • the Python keywords
  • the decision code segement
  • the looping code segment
  • the run time error (exception) handling code segment
• Run the sample script with the following given command line options and study its output:

  • python3 sample.py

  • python3 sample.py test

  • python3 sample.py 2>/dev/null

  • python3 sample.py test 2>/dev/null

Investigation 3 - exploring and using Python's built-in functions

Part I - Interactive (leaning) mode: using the Python Interactive Shell

• In this mode, you can instruct the Python Interpreter to execute python statement or python expression one at a time, call a function, or display the representation of a python data object.
• To start the Python version 3 Interactive shell, type the command

  [raymond.chan@mtrx-node05pd lab1]$ python3

  at the Linux command prompt.
• You should get a startup message similar to the following:

  [raymond.chan@mtrx-node05pd lab1]$ python3
  Python 3.6.8 (default, Apr  2 2020, 13:34:55) 
  [GCC 4.8.5 20150623 (Red Hat 4.8.5-39)] on linux
  Type "help", "copyright", "credits" or "license" for more information.
  >>>

• Note that when you see the >>> Python interactive shell prompt, which indicates that the Python Interpreter is listening and waiting to carry out your instruction written in the Python language. Try the following commands at the python command prompt, and record their outputs for future reference:
  • >>> copyright
  • >>> credits
  • >>> license
  • >>> help
• The output of the last command should tell you how to enter the interactive help, or how to get help on a Python Object. You should see the following message when entering the interactive help utility:

  Welcome to Python 3.6's help utility!
  
  If this is your first time using Python, you should definitely check out
  the tutorial on the Internet at https://docs.python.org/3.6/tutorial/.
  
  Enter the name of any module, keyword, or topic to get help on writing
  Python programs and using Python modules.  To quit this help utility and
  return to the interpreter, just type "quit".
  
  To get a list of available modules, keywords, symbols, or topics, type
  "modules", "keywords", "symbols", or "topics".  Each module also comes
  with a one-line summary of what it does; to list the modules whose name
  or summary contain a given string such as "spam", type "modules spam".
  
  help>

• Please note that the prompt changed from >>> to help>. Try the suggestion and feel free to explore the interactive help utility. Simple press the Enter key to get out of the interactive help utility.
• At the >>> prompt, type dir() to call the built-in function dir without function argument to display a list of data object names known to the Python interpreter at the moment. You should get a list similar to the following:

  >>> dir()
  ['__annotations__', '__builtins__', '__doc__', '__loader__', '__name__', '__package__', '__spec__', 'x']
  >>>

• We are interested in the object named __builtins__. We can ask the Python interpreter to tell use more about the __builtins__ by passing __builtins as a function argument to the dir() function:

  ['ArithmeticError', 'AssertionError', 'AttributeError', 'BaseException', 'BlockingIOError', 
  ...
  ValueError', 'Warning', 'ZeroDivisionError', '_', '__build_class__', '__debug__', '__doc__',
  '__import__', '__loader__', '__name__', '__package__', '__spec__', 'abs', 'all', 'any',
  'ascii', 'bin', 'bool', 'bytearray', 'bytes', 'callable', 'chr', 'classmethod', 'compile', 
  'complex', 'copyright', 'credits', 'delattr', 'dict', 'dir', 'divmod', 'enumerate', 'eval', 
  'exec', 'exit', 'filter', 'float', 'format', 'frozenset', 'getattr', 'globals', 'hasattr',
  'hash', 'help', 'hex', 'id', 'input', 'int', 'isinstance', 'issubclass', 'iter', 'len', 
  'license', 'list', 'locals', 'map', 'max', 'memoryview', 'min', 'next', 'object', 'oct', 
  'open', 'ord', 'pow', 'print', 'property', 'quit', 'range', 'repr', 'reversed', 'round', 
  'set', 'setattr', 'slice', 'sorted', 'staticmethod', 'str', 'sum', 'super', 'tuple', 
  'type', 'vars', 'zip']

• The above output shows a list of the so-called built-in run-time error codes and bulit-in functions. We are going to learn how to use them effective to save our coding effort when writing Python programs/scripts.
• Let start with the following built-in functions:
  • print()
  • help()
  • type()
• Study the output of the following command at the >>> prompt and keep them for future reference:

  >>> help(help)
  
  >>> help(print)
  
  >>> help(type)
  
  >>> type(type)
  
  >>> type(help)
  
  >>> type(print)

Part II - Script (execution) mode: creating Python script

• In this part we will start writing our very first python script. The scripts we are going to try will be very basic and it is use to help us practice the language syntax and explore the foundational coding skills, such as:
  • sending text to the screen,
  • storing value in an data object,

Task 1 - Python script using builtin Functions

Creating the "Hello World" Python Script

You will learn to create a simple python script in this section. This python script will just call the Python builtin function print() to send the text "hello world" to the screen. The "hello world" is an old traditional first program students usually are taught to create, which is based on the first programming example from the first C programming text co-written by Dennis Ritchie, the creator of the C programming language and Brian Kernighan. You will learn how to run the Python script in the Python3 shell as well as to learn how to run the Python script from the bash shell.

Perform the following steps:

1. Create a new Python file in your ~/ops435/lab1 directory. Call it lab1a.py. The first Python code we will write is going to call the print() function. A function is code that has been defined somewhere. Functions can take arguments, use these arguments in some way, and then usually, but not always, return a result. The first function we will use is the "print()" functions, it's sole purpose is to send data to the screen.
   
   
2. Add the following line into your source code file:

   print()

   And run it from the command-line:

   python3 ./lab1a.py

   You will notice that nothing is printed even though we called the "print()" function. This is because we didn't pass any arguments to it, lets try again.
   
   
3. Modify your call to print() to include an argument ('hello world'):
   

   print('hello world')

   This time we should now see that the python function "print()" has sent something to the screen - the words 'hello world'. In Python a word or a bunch of characters like 'hello world' is called a 'string'. In the above example, a string was passed as an argument to the print function. These words are important for understanding and talking about different aspects of code.
   
   
4. Note that there are similarities between the Python print() function and the Bash echo command, but Python is more picky than bash (which is a good thing). Try to run print without the brackets or without the quotes to see what happens.

Reading errors
One of the things that makes a good programmer is debugging skills. The first and most important debugging technique is reading and understanding error messages. Try to understand what the errors are saying even if you think you already know what the problem is and already have some idea about how to fix it.

5. Write the following code into our Python file. Note the she-bang line at the top of the file to run this script in the python3 environment. You will need to add this she-bang line for all python scripts you create for this course.

   #!/usr/bin/env python3
   '''Description: This program will output "hello world" to the screen.'''
   
   # Any line that starts with a "#" is also known as a comment,
   # these lines are ignored by the python interpreter even if
   # they contain code. The very first line is called a Shebang line, 
   # it is used to tell the system which interpreter to 
   # use(python2, python3, bash, etc). 
   
   print('Hello world')

6. Another way of running a Python program is executing it directly, e.g.:

   ./lab1a.py

   Note that the file will need execute permissions even though you ran it just fine earlier. Why is that?
7. Download the check script and check your work. Enter the following commands from the bash shell.

    cd ~/ops435/lab1/
    pwd #confirm that you are in the right directory
    ls lab1a.py #confirm that you have the lab1a.py script in your directory
    ls CheckLab1.py || wget https://ict.senecacollege.ca/~raymond.chan/ops435/labs/LabCheckScripts/CheckLab1.py
    python3 ./CheckLab1.py -f -v lab1a

8. Before moving on to the next step make sure you identify any and all errors in "lab1a.py". When the check script tells you everything is "ok", you may proceed to the next step.

Investigation 4 - exploring Python's built-in data objects

• integer object
• string object

Investigation 5 - exploring on how to get Python to do maths

• Math operators

LAB 1 SIGN-OFF Upload the following files individually to Blackboard

• gitlog.txt: contains the output of the command "git log" from Task 3
• repo_tree.txt: contains the output of the command "tree -a" from Task 3
• lab1_check.txt: contains the output of the command "python3 ./checkLab1.py -f -v"

Lab Review

1. What is a git repository?
2. What kinds of data can be stored in a git repository?
3. What is a git branch?
4. What is the name of the definitive branch in a git repository?
5. What is a "pull request" related to a branch in a git repository?