Introduction to Python

• Week 3 focuses on introducing the Python programming language

Learning Objectives

• Create a first Python program
• Describe what will happen when running a program which produces an error
• Declare a variable and determine value
• Apply comments in your code, both single and multiline

What is Python?

• Python is a general-purpose language often used in scripting roles
• Python is both a programming and scripting language
• Python is an interpreted, object-oriented, high-level language

Programming vs. Scripting Language

• A program is executed, the source is first compiled
• A program implements a sequence of instructions for a computer to perform a task
• A script gets interpreted
• A script is written in a scripting language
• A scripting language controls another software application

History

• Guido van Rossum invented Python in the early 90s in the Netherlands
• Python's conception occurred in the late 1980s, and its implementation started in December 1989
• Guido Van Rossum is a fan of "Monty Python's Flying Circus"
• Python got named after Monty Python
• Python has been open sourced since the beginning

A Short History Of Python

• The Conception was in the late 80s
• The implementation started in Dec 1989
• Python 0.9 was released in Feb 1991
• Python 1.0 was released in Jan 1994
• Python 2.0 was released in Oct 2000
• Python 3.0 was released in Dec 2008
• Python 3.7 was released in Jun 2018

Why Use Python?

• Simplicity, readability, and ease of use
• Python applications:
• Systems programming
• GUI programming
• Database programming
• Component integration
• Gaming
• XML
• Robotics
• Web applications
• Data science and visualization
• Machine learning
• Vulnerability testing

Five of the Many Reasons to Use Python

• Easy to Learn and Use
• Versatile
• Large and Active Community
• Cross-Platform Compatibility
• Open-source

Who Uses Python Today

• Python is applied in revenue-generating products by real companies
• Google utilizes Python extensively in its web search system
• Intel, Cisco, Hewlett-Packard, Seagate, Qualcomm, and IBM use Python for hardware testing
• ESRI uses Python as end-user customization tool for its popular GIS mapping products
• YouTube video sharing is largely written in Python

Requirements

• Python 3 Interpreter or above
• IDE Options can be offline or online
• Offline
• Pycharm
• Anacoda/Jupyter Notebook
• Online:
• onlinegdb.com
• colab.google
• replit.com
• online-python.com/online_python_compiler

Installing Python

• Download the latest version of Python from https://www.python.org/downloads/
• After the installation process starts. you will see a pop-up
• Once installed, open Python, you are prompted with >>> for single line commands

Using PyCharm

• Preferably download the community edition
• Run the installer and follow the steps
• installation options:
• 64-bit launcher: Adds a launching icon to the Desktop
• Open Folder as Project: Adds an option to the folder context menu that will allow opening the selected directory as a PyCharm project
• .py: Establishes an association with Python files to open them in PyCharm
• Add launchers dir to the PATH: Allows running this PyCharm instance from the Console without specifying the path to it
• Run PyCharm from the Windows Start menu/desktop shortcut, or from the launcher batch script/executable in the installation directory under bin.

Creating a Python Project in PyCharm

• When opening PyCharm for the first time, the Welcome Screen will appear and it's time to create your project
• The project is your central view for running and debugging code, using the Python console and system terminal, and managing tests, version control, databases, and frontends
• Create the project:
• Different project types can be created, in this case create a simple pure Python project
• Specify the project location by clicking the Browse button in the Location field
• Create a dedicated environment for each project is best practice. The Project venv will do the job on default
• Switch to Custom environment to use an existing environment or specify other environment types
• Click Create when ready

Creating a Python File in PyCharm

• Select the project root in the Project tool window, right-click, and select File | New
• Select the context menu, type the filename

Running Python

• Running Python Using Command Line
• Type in commands such as:

• print ("Hello World")

• Printing the line will output "Hello World"
• Running in PyCharm
• Either right-click the editor and select Run from the context menu
• Press Ctrl+Shift+F10
  • Since this Python script contains a main function, you can click in the gutter
  • You'll see the popup menu of the available commands, and choose Run

Python Code Execution

• Source code translates to byte code
• This byte code gets run by the Python Virtual Machine
• The code is automatically compiled and then interpreted
• The file extension for source code is ".py"
• The file extension for byte code is ".pyc"

Indentation Matters

• Indentation is crucial in Python, as it defines code blocks instead of curly braces
• Consistent indentation (usually 4 spaces) is essential for proper program flow and to avoid errors

Comments in Python

• Interpreter ignores lines in Python code, these are comments
• Comments enhance the code's readability

• Single-line comments

• """ Multiple line comments """

Keywords in Python

• Keywords in Python are reserved words that can not be used as a variable name

Print Command

• Produces text output on the console
• print("Message") prints a message
• print(Expression) prints the given text message or expression value on the console
• print(Item1, Item2, ..., ItemN) prints several messages and/or expressions on the same line. Elements separated by commas print with a space between them. A comma at the end of the statement will not print a newline character
• Print command examples:
• print("Hello, world!") outputs Hello, world!
• age = 45
• print("You have", 65 - age, "years until retirement") prints You have 20 years until retirement

Expressions

• An expression is a data value or set of operations to compute a value
• 1+4*3
• 42
• Arithmetic operators
• + addition
• - subtraction/negation
• * multiplication
• / division
• // floor division or integer division
• % modulus a.k.a remainder
• ** exponentiation
• Precedence sets the order in which operations are computed
• / % ** have a higher precedence than + -
• Parentheses can be used to force a certain order of evaluation
• (1 + 3) * 4 is 16

Real Numbers or Floating Point

• Python can also manipulate real numbers
• Example: 6.022, -15.9997, 42.0, 2.143e17
• The operators +, -, *, /, %, and ** all work for real numbers
• The / (division) operator produces an exact answer: 15.0 / 2.0 is 7.5
• Order of operations in real numbers is the same as for integers
• When integers and reals are mixed, the result is a real number
• Conversion occurs on a per-operator basis

Math Commands

• Python has useful, pre-built commands/functions for calculations
• abs(value) - absolute value
• ceil(value) - rounds up
• cos(value) - cosine in radians
• floor(value) - rounds down
• log(value) - logarithm, base e
• log10(value) - logarithm, base 10
• max(value1, value2) - larger of two values
• min(value1, value2) - smaller of two values
• round(value) - nearest whole number
• sin(value) - sine, in radians
• sqrt(value) - square root
• To use many math commands, include the import statement at the start:
• from math import *
• import math

From math import * vs import math

• from math import *
• This imports all names from the module and puts them into the current namespace
• Functions/constants can be used from math without the math.file prefix prefix
• import math
• Use import math for clear and safe access to functions and constants from the math module
• It provides explicit use of the math module, and improves code readability
• Helps prevent naming conflicts by separating the module from your local variables

Relational expressions

• Use of comparisons involving values
• Evaluate to a boolean value based on the condition
• Relational Operators:
• == Equal to
• != Not equal to
• < Less than
• > Greater than
• <= Less than or equal to
• >= Greater than or equal to

Logical expressions

• Expressions used to combine conditions, evaluate to True or False
• Essential for making decisions and controlling the flow of a program
• Logical Operators:
• and - Returns True only if both operands are True
• or - Returns True if at least one operand is True
• not - Reverses the value of an operand (True becomes False, False becomes True)

Operator Precedence

• Exponentiation ()** has highest precedence
• Multiplication (*) and Division (/), Floor Division (//) is evaluated left-to-right
• Addition (+) and Subtraction (-) evaluated left-to-right
• Comparison Operators (==, !=, <, >, <=, >=)
• Logical Operators (not, and, or) have the lowest precedence
• Parentheses override the default precedence order

Variables

• A named piece of memory that stores a value, explicit declaration of data type is not required
• Python infers the type from the value
• Usage:
• Compute an expression's result, store that result into a variable, and use that variable later in the program
• Assignment statements store a value into a variable
• Syntax: name = value

Rules for Python Variables

• Start with a letter or the underscore character
• Begin with a number
• Only contain alpha-numeric characters and underscores (A-z, 0-9, and _ )
• Case-sensitive (name, Name, and NAME are treated individually)
• Reserved words (keywords) are not allowed

Data Types

• Data types classify the kind of data a variable stores, determining the values and operations
• Python is dynamically typed. The data type of a variable is determined at runtime
• Numeric Types:
• Integers (int) represent whole numbers, positive, negative, or zero (e.g., -5, 0, 1024)
• Floats (float) represent decimal numbers (e.g., 3.14, -9.25)
• Complex Numbers (complex) represent numbers with imaginary and real components
• Text Type:
• Strings (str) represent sequences of characters enclosed in single or double quotes
• Logical Type:
• Booleans (bool) represent logical values, True or False
• Collection Types:
• Lists (list) lists of elements enclosed inside a square brackets [] can be modified
• Tuples (tuple:) list of elements enclosed in parentheses () cannot be modified
• Sets (set:) unordered collections of unique elements enclosed in curly braces {}.
• Dictionaries (dict:) unordered collections of key-value pairs enclosed in curly braces {} must be unique

Choosing the Right Data Type

• Use integers for whole numbers i.e. counting, indexing
• Use floats for decimal numbers and calculations
• Use strings for text data, addresses
• Use booleans for logical true/false statements
• Use lists a sequence of elements allowed for editing
• Use tuples for read only code
• Use set for unique elements when order does not matter
• Use dictionaries to store key-value pairs when efficient retrieval by key is needed

Casting

• Converting one data type into another
• Function:
• str() converts a value to string
• float() converts a value to float
• int() coverts to an integer
• bool() converts a value to true or false

Input

• input() reads a number from user input
• Assign (store) the result of input into a variable

Strings

• Strings can be single-line, or multi-line
• Display a string literal by print()
• String Placeholders
  • {} (curly braces format)
  • % (percent format)
  • f (f-string format)

Strings Placeholders {}

• {} and .format() can replace variables in complex strings
• Use {Number} for numbered index placeholders
• Use {variable} for named placeholders

Strings Placeholders %

• %d is used to format integers
• %s is used to format strings
• %.2f is used to format a float with "point 2" precision digits

The percent sign (%) placeholder

• Obsolete method of string formatting, replaced with "fstrings"
• Formatting Characters with %:
  • `%d formatting integers
  • `%f formatting floats.
  • `%s formatting string values
  • `%c Used to format Single Characters

Modifiers

• Adjusts the value to the left in assigned space
• Padding the numbers left, using spaces
• Decimal point precision in floats that are left

String Placeholders F

• Use the f tag at the start of Strings, this method is preferable to others

String Formatting Functions

• upper() : string to upper case
• lower() : string to lower case
• title() : converts each word to upper case
• captilize() : convert the first word to upper case
• split(): : splits a string to separated at a certain separator, and returns a list
• replace() : replaces a phrase or character with another one

String Formatting Functions

len(): count the numbers in a char or string

NUMBER Formatting Functions

• Number data types store numeric values.
• Immutable: means that changing the value of a number data type results in a newly allocated object

Integer formating

Integer formating: this function returns a whole number of the specified number floor: method rounds a number DOWN to the power of x pow: The pow(x, y) function returns the value of x is a rounded version of the specified number.

Problem set

• Problem 1 to problem 9 are practice tasks for the use of everything learned in this lesson