Python Programming: Installation and Introduction

Announcements and Introduction

• A new full-stack web development batch, Delta 4, is starting on February 15th at Apna College.
• A special offer for interested students is valid until 6 PM on February 13th.
• Enrollment link is available in the description box.
• The tutorial covers the complete Python language from basics to object orientation.
• Mini-games will be created to enhance understanding of Python.
• Notes and slides are available for download in the description box.
• No prior coding experience is needed to start this tutorial.
• The goal is to learn practical Python programming and core concepts.
• Slides and notes are available on the Apna College website.

Setting up Development Environment

• Code is written in code editors, not by hand.
• Visual Studio Code (VS Code) is recommended as a free editor.
• Installation involves downloading Python and VS Code.
• For Windows, Python can be downloaded from python.org

Python Installation on Windows

• Go to python.org downloads to download the installer.
• During the installation process, two check boxes must be checked: one for admin privileges and one for adding Python to PATH.
• After installation, the setup will show a "successful" message.

Python Installation on Mac

• Python can be downloaded from python.org/downloads using the yellow download button for the latest version.
• The downloaded package should be double-clicked to start the installation.
• Agree to the terms.
• Enter the password to "install the software".

Verifying Python Installation

• Run python3 --version or python3 -V in the terminal or command prompt to verify the installed version.
• The same command works on both Mac and Windows.

Installing Visual Studio Code (VS Code)

• Search "download VS Code" on the internet to find the download link.
• The site is code.visualstudio.com.
• Download the version appropriate for the operating system (Windows, macOS, Linux).
• For Windows, check all the checkboxes during installation.
• Launch VS Code.

Introduction to Programming Fundamentals

• Programming involves giving instructions to a machine (computer or laptop) through code.
• Computers do not understand human languages directly, so programming languages like Python, Java, or C++ are used.
• Just as one would need to speak French in France, one must use a programming language to communicate with a computer.
• Computers understand 0s and 1s (machine language), so translators are needed to convert Python code.
• Translators convert high-level languages (like Python) to machine language.

Understanding Translators

• Translators can be compilers or interpreters.
• Python uses an interpreter to convert Python code to machine-readable language.
• Python is referred to as a high-level language due to its human-readable syntax.

Properties of Python

• Simple and Easy: Python is simple and easy to understand, making it suitable for beginners.
• Versatile: Python can be used across different operating systems and has wide application.
• Open Source: Python is an open-source language.
• It can be used in data science, machine learning, AI, web development (with frameworks like Django), and game development.

Writing the First Program

• Open VS Code.
• Create a new file to start writing code (Command+N or Ctrl+N).
• Save the file with a ".py" extension, such as "first_program.py".
• The ".py" extension indicates that the file is a Python file.

Python First Program and Output

• The initial program in Python typically involves displaying "Hello World" as output.
• The print() function in Python is used to display output on the screen.
• Whatever is enclosed within the parentheses and double quotes of the print() function is displayed verbatim.
• You can print other texts as output simply by changing the text within the double quotes such as a name or college.
• In the context of coding fundamentals, code usually takes input and produces output.
• For example, using a grinder where raw spices are the input, and ground spices are the resulting output.

Python's Character Set

• Python has a specific character set, including:
  • English uppercase letters (A-Z)
  • English lowercase letters (a-z)
  • Digits from 0 to 9
  • Special symbols present on the keyboard (e.g., -, +, *, /, %, etc.)
  • Whitespaces (blank spaces, tab spaces)
  • ASCII and Unicode characters

Printing Multiple Items on the Same Line

• Multiple items can be printed on the same line by separating them with commas within the print() function.
• Each item separated by a comma will be printed with a space in between.
• For printing items on separate lines, distinct print statements needed.

Python Math Operations

• Python allows basic arithmetic operations such as addition, subtraction, multiplication, and division directly within the print statement.
• print(35+23) will output the sum, which is 58.

Variables in Python

• A variable is a named memory location used to store values.
• It is similar to variables used in mathematics, such as 'a' and 'b' in formulas.
• Example is finding the area of a retangle a * b, or a square a * a. Here a and b are variables.
• A variable's value can be changed.
• Examples of creating variables and assigning values:
  • name = "Shraddha"
  • age = 23
  • price = 25.99
• In Python, the syntax is variable = value, where the variable is on the left and the value to be stored is on the right.
• From right to left side = value is being assigned.
• The value can be a string, integer, or floating-point number.
• A string is a word or a sentence inside double quotes, "".
• Python also lets you use string inside single quotes '' or triple quotes """""".

Memory Allocation

• When a variable like name = "Shraddha" is created, the string "Shraddha" is stored in a memory location, and the variable 'name' points to that location.
• Variables reserve and fix the memory location
• There are many empty spaces and the code picks one and stores the value inside it.
• If the value of a variable changes (e.g., age = 24), the value in the memory location is updated.

Variable Declaration and Printing

• To print the value of a variable, simply use the variable name in the print() function.
• If code has print("name") printed, then the word "name" is being printed.
• It should not have " " because then its like the print(string) case.

Rules for Indentifiers

• Rules when naming variables
• Upper Case and Lower Case Letters, Digits and underscores are allowed.
• Variable name can only use A - Z, a - z, 0 - 9, _.
• Should use a shorter, simpler and meaningful name.
• Use a name that can be easily understood.
• The special symbol is not allowed like "@", "#", etc.

Naming Convention and Practices

• A variable name must begin with a letter (a-z, A-Z) or an underscore (_).
• It should not start with any special character or digit.
• Variables are Case Sensitive.

Data Types

• Strings use "", integers dont have quotations.
• The print() statement is
• int prints integer values.
• str prints string values.

Python as a Typed Language

• Python as a Case Sensitive language, so pay attention to the capital letters in the syntax.
• "A" doesn't equal "a".
• All of Python's syntax should remain similar to how the code was written.

Solving Problems (Sum of Two Numbers)

• When writing code, determine if each value requires addition, subtraction, etc.

Punctuation

• Python uses symbols that are not letters, digits, or identifiers. It is called the Token Punctuation.

File Operations in Python

• Accessing a file involves knowing its location.
• Example: The file "demo.txt" is located at users/amant/desktop/shraddha/.
• Different modes exist, but not all are frequently used.

Opening a File

• After locating a file, use the open() function to access it.
• Pass the file path and mode as arguments to the open() function.

Reading a File

• The read() method retrieves the entire file content as a string.
• Assign the result of f.read() to a variable (e.g., data = f.read()).
• Print the variable to view the file's content.

Closing a File

• After operations, close the file using f.close().
• Closing prevents unauthorized access and modification.

File Modes

• r: Opens the file for reading (default mode).
• w: Opens the file for writing, overwriting existing content.
• x: Creates a new file and opens it for writing.
• a: Opens the file for writing and appends data to the end.
• b: Binary mode for binary files.
• t: Text mode for text files (default).
• +: Opens a disk file for updating (reading and writing).
• Text files are opened by default unless binary mode is specified.

Combining Modes

• Modes can be combined, such as r+ for reading and writing.
• r+ allows both reading and writing operations on the file.
• In r+ mode, the stream is positioned at the start of the file.
• Other examples: w+ (write and read), a+ (append and read).

Reading Methods in Detail

• read() can take an argument specifying the number of characters to read.
• Example: f.read(5) reads the first five characters.
• readline() reads one line at a time.
• Newline characters (\n) are included when using readline().
• Calling read() moves the cursor to the end of the file.
• Subsequent readline() calls may return empty strings.

Reading Line by Line

• The cursor moves to the end of each line after readline().
• If readline() is called after the entire file has been read, it will return an empty string.

Writing to a File

• Open the file in write (w) or append (a) mode.
• w mode overwrites existing content.
• a mode adds data to the end of the file.
• Use f.write() to write data to the file.
• Add newline characters (\n) for proper formatting.

Overwrite vs Append Mode

• Use the write ("w") mode to replace all data or append ("a") mode to add to it

Creating Files

• Opening a non-existent file in w or a mode creates a new file.
• Python automatically creates the specified file if it does not exist.

File Operations in Python

• A sample file was opened in read mode (r+).
• In r+ mode, existing content is overwritten starting from the beginning of the file.
• When opening a file in r+ mode, the pointer is initially at the beginning of the file, allowing for both reading and writing.

Overwriting Files

• Opening a file in r+ mode allows overwriting existing data from the start of the file.
• In r+ mode file, "THIS" was replaced with "ABC", demonstrating the overwriting capability.
• After writing "ABC," the pointer moves to the next position ("S"), affecting subsequent read operations.

Pointers and Streams

• All reading and writing operations are performed through a pointer in the file.
• The pointer's position determines where the next read operation will start.
• After writing, the pointer advances, influencing the starting point of the next read.

Write Plus (w+) Mode

• w+ mode opens a file for both reading and writing, but it truncates the file first.
• Truncating in w+ mode means the file's content is emptied before any operations.
• In w+ mode, the file is emptied, and writing "ABC" adds this content to the previously empty file.

Append Plus (a+) Mode

• The a+ mode opens a file for reading and appending.
• When opening a file in a+ mode, the pointer is positioned at the end of the file.
• In a+ mode, the pointer is placed at the end, and after appending "ABC", the file now contains the original content followed by "ABC".

Summary of File Modes

• Read (r): Simplest mode for reading.
• Write (w): Simplest mode for writing (overwrites or creates a new file).
• Append (a): Simplest mode for appending data to the end of the file.
• Read Plus (r+): Read and overwrite; pointer starts at the beginning, no truncation.
• Write Plus (w+): Read and overwrite, truncates the file before opening.
• Append Plus (a+): Read and append; pointer starts at the end, no truncation.

With Syntax

• The with syntax is used for opening files which automatically closes the file after operation.
• Syntax: with open("filename", "mode") as file_alias:.
• The code within the with block operates on the file stream referred to by file_alias.
• The with syntax ensures the file is automatically closed after the block is executed.

File Deletion

• Files are not deleted with f.delete() but with a special module called "os".
• To delete a file, import the os module.
• The os.remove("filename") function is used to delete a file.

Modules in Python

• Modules are code libraries containing functions that can be imported and used in programs.
• An example of a module is the "os" module, which has functions that interact with the operating system.
• When a module is not installed the user must install it before running, "no module found" is an error when its not installed.
• A pre-installed module will immediately run after importing

Installing Modules

• Modules are installed with "pip install <module_name>".
• PIP is a package installer for python.