Introduction to python notes learn python chapter 1

Chapter 1.1: What is Python?

1.1.1 Overview of Python

Python is a high-level, interpreted programming language designed with readability and simplicity in mind. It was created by Guido van Rossum and first released in 1991. Python’s simple syntax, dynamic typing, and versatility make it one of the most popular programming languages in the world.

1.1.2 Key Characteristics of Python:

1. High-Level Language: Python is a high-level programming language, meaning it abstracts away the complex details of the machine’s hardware. Programmers can focus on writing code rather than worrying about memory management, CPU instructions, or system architecture.

2. Interpreted Language: Python is interpreted, which means the code is executed line by line at runtime rather than being compiled in advance. This makes Python flexible and suitable for scripting and quick prototyping.

3. Object-Oriented and Functional: Python supports both object-oriented programming (OOP) and functional programming paradigms. This allows developers to choose the best approach for a given task, enhancing flexibility.

4. Readable and Clean Syntax: Python’s syntax is designed to be human-readable and easy to understand, even for beginners. This encourages the development of clean, maintainable code.

5. Cross-Platform: Python is cross-platform, meaning it runs on various operating systems like Windows, macOS, and Linux without requiring modifications to the code.

1.1.3 Applications of Python:

Python has broad applications in various domains, including:

• Web Development: Frameworks like Django and Flask make it easy to build web applications.
• Data Science and Machine Learning: Libraries like NumPy, pandas, and TensorFlow enable advanced data analysis and machine learning.
• Automation: Python scripts are often used for automating repetitive tasks.
• Software Development: Python is used for developing applications, system utilities, and software testing.
• Game Development: Libraries like Pygame are used for developing simple 2D games.

Example:

 # A simple Python program that prints "Hello, World!"
print("Hello, World!")

Chapter 1.2: Why Python?

Python has several unique features that make it stand out as a top choice for both beginners and experienced developers.

1.2.1 Easy to Learn and Use:

Python’s clean syntax and straightforward structure make it one of the easiest programming languages to learn, especially for beginners. Its syntax resembles plain English, which means fewer lines of code are needed to accomplish tasks compared to languages like C++ or Java.

Example: Compare the following Python and Java code to print "Hello, World!":

print("Hello, World!")

public class HelloWorld {
    public static void main(String[] args) {
        System.out.println("Hello, World!");
    }
}

now

1.2.2 Versatile and General-Purpose:

Python is a general-purpose language, meaning it can be used for many different types of programming tasks, such as:

• Web development.
• Data analysis.
• Machine learning.
• Automation scripts.
• Application development.

1.2.3 Extensive Libraries and Frameworks:

Python comes with a large standard library that provides tools suited to many tasks, from working with regular expressions to handling files, databases, and more. Additionally, Python has a huge ecosystem of third-party libraries and frameworks that extend its functionality.

Some popular libraries and frameworks include:

• Django/Flask: For web development.
• NumPy/pandas: For data analysis.
• Scikit-learn/TensorFlow: For machine learning.
• Pygame: For game development.
• BeautifulSoup/Scrapy: For web scraping.

1.2.4 Strong Community Support:

Python has a vast, active community of developers. If you ever run into issues or have questions, there are countless resources available, including documentation, forums, and tutorials. The community also regularly contributes to the development of Python itself, as well as its libraries.

1.2.5 Cross-Platform Compatibility:

Python can run on a variety of platforms, such as Windows, macOS, and Linux, with minimal changes to the code. This cross-platform nature means Python programs can be developed and tested on one system and deployed on another with ease.

1.2.6 High Demand and Career Opportunities:

Python is one of the most in-demand programming languages in the job market, especially in fields like web development, data science, machine learning, and automation. Mastering Python can open up a wide range of career opportunities.

1.2.7 Code Reusability and Modular Design:

Python promotes modularity, allowing you to break down your programs into reusable components. Using functions, classes, and modules, you can write code once and use it multiple times across different parts of your program or even in other projects.

Chapter 1.3: Installation of Python

 Before you can start writing Python programs, you need to install Python on your computer.

1.3.1 Downloading Python

Python is free and open-source, and you can download it from the official website:

1. Visit the Python website: Go to python.org.

2. Select your operating system:

   • For Windows, download the Windows installer.
   • For macOS, download the macOS installer.
   • For Linux, Python usually comes pre-installed, but you can update it or install it using your distribution's package manager (like apt for Ubuntu or yum for Fedora).

3. Download the latest version: Python 3.x is the recommended version. Avoid Python 2.x, as it is no longer supported

1.3.2 Installing Python on Different Operating Systems

Windows Installation:

1. Run the installer: Double-click the downloaded file.
2. Check the "Add Python to PATH" box: This allows you to run Python from the command prompt.
3. Choose "Install Now": The installer will set up Python on your system.

macOS Installation:

1. Run the installer: Double-click the downloaded file.
2. Follow the prompts: The installer will guide you through the installation process.
3. Verify installation: Open the terminal and type python3 --version to check that Python was installed correctly.

Linux Installation:

Python is usually pre-installed on most Linux distributions. To check if Python is installed, open a terminal and type python3 --version. If it is not installed or needs an update:

sudo apt update
sudo apt install python3

1.3.3 Verifying the Installation

Once Python is installed, you can verify it by running the following command in the terminal or command prompt:

 

 python3 --version

Chapter 1.4: First Python Program: print("Hello, World!")

1.4.1 Writing Your First Python Program

Once Python is installed, the next step is to write and execute your first Python program. A classic and simple first program is printing "Hello, World!" to the screen.

here is how to do it -

 print("Hello, World!")

This is output : pre

 Hello, World! < pre/>

1.4.2 Breaking Down the Code

• print(): This is a Python built-in function that outputs text to the console.
• "Hello, World!": The text inside the parentheses is a string, denoted by double or single quotes. It is the message that will be printed.

1.4.3 Running Your First Program

You can run this program in various environments:

1.4.3.1 Python Shell

The Python shell is an interactive environment where you can run Python commands line by line.

• Open the command prompt or terminal.
• Type python3 or python to start the Python interactive shell.
• Type the following line and press Enter:

1.4.4 Important Notes

• Python programs end with the .py extension (e.g., hello.py).
• Python is an interpreted language, so you do not need to compile it. The Python interpreter processes the code directly.

 

Chapter 1.5: Comments in Python

---

Comments in Python are used to explain code and make it more readable. They are ignored by the Python interpreter and are purely for the benefit of the developer. Comments can be used to leave notes, describe complex logic, or temporarily disable code.

1.5.1 Types of Comments

1.5.1.1 Single-line Comments

A single-line comment starts with a # symbol. Everything after the # on that line is considered a comment and is ignored by Python.

Example:

In the example above, # This is a comment is ignored, and only the print("Hello, World!") statement is executed.

1.5.1.2 Multi-line Comments

Python doesn’t have a dedicated syntax for multi-line comments. However, you can create a multi-line comment by using triple quotes (''' or """). These are technically multi-line strings, but they can be used as comments if not assigned to a variable.

Example:

Another way to write multi-line comments is to use # at the beginning of each line.

Example:

 

1.5.2 Why Use Comments?

• Clarity: Comments help others (and future you) understand what the code is doing.
• Documentation: They serve as documentation, explaining how specific parts of the code work.
• Debugging: Temporarily commenting out a line of code is a common debugging practice.

1.5.3 Best Practices for Comments

• Use comments sparingly—only when necessary.
• Avoid obvious comments (e.g., # This line prints "Hello, World!" is unnecessary when the code itself makes that clear).
• Keep comments up-to-date with the code to avoid confusion.

Chapter 1.6: Python Shell and IDE

1.6.1 Python Shell

The Python shell (also known as the REPL - Read-Eval-Print Loop) is an interactive command-line interface that allows you to execute Python code one line at a time. It’s ideal for quickly testing small pieces of code and experimenting with Python features.

How to Access Python Shell:

1. Windows:
   • Open the Command Prompt by typing cmd in the search bar.
   • Type python and press Enter.
2. Mac/Linux:
   • Open the Terminal.
   • Type python3 and press Enter (since many Mac/Linux systems use python3 by default).

If Python is correctly installed, you will see something like this:

 

 Python 3.x.x (default, Month Date Year, Time)
[GCC version info] on platform info
Type "help", "copyright", "credits" or "license" for more information.
>>>
The >>> prompt is where you can start typing Python code.

Advantages of Python Shell:

• Instant Feedback: You can see the result of each command immediately after executing it.
• Simple Learning Tool: Ideal for beginners to test Python concepts without creating files.

Basic Commands in Python Shell:

 >>> 2 + 3
5
>>> print("Hello, World!")
Hello, World!

The Python shell evaluates each expression and displays the result, making it useful for calculations and testing snippets of code.

Exiting Python Shell: Windows/Mac/Linux: Type exit() or press Ctrl + Z and then Enter.

1.6.2 Integrated Development Environment (IDE)

An Integrated Development Environment (IDE) provides a more sophisticated environment for writing, running, and debugging Python code. While the Python shell is excellent for quick tests, an IDE is better for writing larger programs. IDEs offer features like syntax highlighting, debugging, code completion, and more.

Popular Python IDEs:

1. IDLE (Integrated Development and Learning Environment):

   • Comes bundled with Python.
   • Good for beginners and easy to use.
   • Offers a script editor along with a Python shell.

   How to Use IDLE:

   • When you install Python, IDLE is installed automatically.
   • Open IDLE from your applications.
   • You can write scripts in the editor and run them directly.

2. PyCharm:

   • One of the most popular and powerful Python IDEs.
   • Provides features like advanced code completion, error detection, and integrated version control.
   • Offers both free (community) and paid (professional) versions.

   How to Install PyCharm:

   • Download PyCharm from the official website: JetBrains PyCharm.
   • Install it and configure the Python interpreter.

3. Visual Studio Code (VS Code):

   • A lightweight, open-source code editor with Python support.
   • You need to install the Python extension to enable Python features like IntelliSense, linting, and debugging.

   How to Set Up Python in VS Code:

   • Download and install VS Code: VS Code.
   • Install the Python extension by Microsoft from the Extensions marketplace.
   • Select the Python interpreter through Ctrl + Shift + P -> Select Interpreter.

4. Jupyter Notebook:

   • Commonly used for data science and machine learning projects.
   • Provides an interactive interface where you can combine code, text, and visualizations.
   • Popular in educational settings and for research projects.

   How to Install Jupyter Notebook:

   • Install via pip: pip install notebook.
   • Run it by typing jupyter notebook in the terminal. It opens in a web browser

6.3 Which One Should You Use?

• For Beginners: Start with IDLE or Python Shell. These are simple to use and require no setup.
• For Professional Development: As you progress, try IDEs like PyCharm or VS Code, as they offer tools for larger projects and more efficient coding.
• For Data Science: Jupyter Notebook is widely used in data science due to its rich display of output and ease of use.

1.6.4 Writing and Running Python Scripts

In the Python shell, you can write individual lines of code, but for larger programs, you'll need to write your code in files (scripts) and run them from the IDE or command line.

Steps to Run Python Script:

1. Create a Python File: Write your Python code in a file with a .py extension, for example, hello.py.
2. Run from Command Line:
   • Open the command prompt or terminal.
   • Navigate to the folder where your Python file is located.
   • Type python hello.py and press Enter to execute the script.

Running Scripts in IDEs:

• In most IDEs like PyCharm, VS Code, or IDLE, you can simply click the "Run" button to execute the script.

1.6.5 Conclusion

• The Python Shell is excellent for quick testing and learning basic concepts interactively.
• IDEs provide robust environments for more advanced projects, offering features like debugging, version control, and code navigation.
• As a beginner, using the Python shell or IDLE is a good starting point. As you grow comfortable, transitioning to an IDE like PyCharm or VS Code will enhance your productivity.

 

1.7.3 Comparison: Python Shell vs IDE

Feature	Python Shell	IDE (e.g., PyCharm, VS Code)
Interactivity	High (execute code line by line)	Lower (full scripts or projects)
Ease of Use	Easy to start, no setup required	Requires setup and installation
Best for	Learning and testing small code snippets	Large projects, debugging, and deployment
Features	Limited, basic output and interaction	Advanced features like debugging, project management, version control
Persistence of Code	No (code is not saved)	Yes (project files and code are saved)

Basic syntax in python 

python Chapter 1.7: Basic Syntax and Code Structure

Understanding the basic syntax and code structure of Python is fundamental for writing error-free programs. Python has a very clean and simple syntax, which makes it easy to learn and use compared to other programming languages. Let’s explore Python’s basic syntax rules and how code is structured.

1.7.1 Python Code Structure

Python programs consist of statements that are executed sequentially, starting from the first line of the program. The general structure of a Python script includes:

• Statements: These are instructions for the interpreter to perform an action.
• Expressions: These are pieces of code that are evaluated and result in a value.
• Functions and classes: These are defined using def and class keywords, respectively.

1.7.2 Basic Python Syntax Rules

1.7.2.1 Case Sensitivity

Python is case-sensitive, which means that Hello and hello are considered different identifiers. You need to be consistent with the case you use in variable and function names.

 

name = "John"
Name = "Doe"

print(name)  # Output: John
print(Name)  # Output: Doe

1.7.2.2 Indentation

Python uses indentation (whitespace at the beginning of a line) to define blocks of code, such as loops, conditionals, and function definitions. Unlike other languages that use curly braces {} or keywords like begin and end, Python strictly relies on indentation to define code structure.

• Indentation level: Typically, four spaces are used for indentation, but you can also use a tab, as long as you are consistent.
• SyntaxError: If you don't use the proper indentation, Python will raise a SyntaxError.

Example: 

 

if True:
    print("This is indented correctly")  # This is inside the block
    print("This is also part of the block")
# No indentation here, meaning we are outside the block

c

1.7.2.3 Line Breaks and Continuation

Python generally expects one statement per line, but if a statement is too long, you can split it into multiple lines using a backslash (\) for line continuation.

Example

long_variable_name = "This is a very long string that continues " \
                     "on the next line using a backslash."

You can also continue lines inside parentheses (), brackets [], or braces {}, and Python will automatically recognize the continuation.

total = (1 + 2 + 3 +
         4 + 5 + 6)

1.7.2.4 Comments

As discussed in Chapter 1.6, comments are pieces of text in the code that are ignored by the interpreter. Python supports both single-line and multi-line comments.

single line comment

# This is a comment

multi line comment using tripple quotes

"""
This is a multi-line comment.
"""

1.7.2.5 Variables and Assignments

In Python, variables are dynamically typed, meaning you do not need to declare their type explicitly. You can assign any value to a variable, and its type is determined by the value it holds.

Example:

 x = 10        # Integer
y = 3.14      # Float
name = "Alice"  # String

1.7.2.6 Printing Output

To output data to the console, you use the print() function.

 Example:

 

print("Hello, World!")
print(x)

1.7.3 Basic Data Types Python has several built-in data types, including: Integers: Whole numbers, e.g., 5, 100, -20. Floats: Numbers with decimal points, e.g., 3.14, -0.5. Strings: Text data, enclosed in quotes, e.g., "Hello, World!". Booleans: Represents truth values, either True or False. 1.7.4 Conditional Statements Python uses if-else statements to control the flow of a program based on conditions. syntax-

 if condition:
    # Block of code to execute if condition is True
elif another_condition:
    # Block of code to execute if the first condition is False and this one is True
else:
    # Block of code to execute if all conditions are False

Example -

x = 10

if x > 5:
    print("x is greater than 5")
elif x == 5:
    print("x is equal to 5")
else:
    print("x is less than 5")

1.7.5 Loops Python supports two types of loops: for loops and while loops. 1.7.5.1 For Loop The for loop is used to iterate over a sequence (such as a list or a range of numbers) Example -

for i in range(5):  # range(5) gives numbers from 0 to 4
    print(i)

1.7.5.2 While Loop The while loop repeats a block of code as long as a condition is true. Example :

x = 0
while x <5: 1="" by="" increment="" print="" x="">

1.7.6 Functions Functions in Python are defined using the def keyword. They allow you to group a set of statements together and reuse them multiple times. syntax :

def function_name(parameters):
    # Block of code
    return value
    
    

Example :

def greet(name):
    print("Hello, " + name)

greet("Alice")

In the example, greet("Alice") calls the greet function with "Alice" as an argument, and the function prints "Hello, Alice". 1.7.7 Python's Code Execution Flow Python executes code sequentially, from top to bottom, unless instructed otherwise by control statements such as conditionals (if), loops (for, while), or function calls. Start from the top: The interpreter reads and executes code from the first line. Conditional branching: When it encounters an if statement, it decides which branch of the code to execute based on the condition. Loops: Loops are executed as long as the specified condition is true. Function calls: When a function is called, Python jumps to the function’s code and then returns to where the function was called after execution.