Python Basics: Syntax, IDEs, and First Programs

What is Python?

Python is a high-level, interpreted, and general-purpose programming language known for its simplicity and readability. It supports multiple programming paradigms, including procedural, object-oriented, and functional programming. Python is widely used in web development, data science, artificial intelligence, automation, and scripting.

Key Features of Python

• Easy to Learn: Simple and readable syntax, resembling English.
• Interpreted: Executes code line-by-line, making debugging easier.
• Cross-Platform: Runs on Windows, macOS, Linux, and more.
• Extensive Libraries: Rich standard library and third-party packages (e.g., NumPy, Pandas, Django).
• Dynamic Typing: No need to declare variable types explicitly.

Setting Up the Python Environment

To start programming in Python, you need to set up a Python interpreter and an Integrated Development Environment (IDE).

Python Interpreter

• Python code is executed using an interpreter, which translates and runs the code line-by-line.
• You can download Python from the official website.
• Verify installation by running in the terminal:

  python --version
  

Popular IDEs for Python

Writing Your First Python Program

A Python program consists of statements written in a .py file. Let’s write a simple program to print "Hello, Nepal!":

# hello.py
print("Hello, Nepal!")

How to Run the Program

1. Save the code in a file named hello.py.
2. Open a terminal and navigate to the file’s directory.
3. Run the program using:

   python hello.py
   

   Output:

   Hello, Nepal!
   

Python Syntax Basics

Python syntax is designed to be clean and intuitive. Below are some fundamental rules:

Indentation

• Python uses indentation (whitespace) to define blocks of code (unlike braces {} in C/Java).
• Example:

  if 5 > 2:
      print("Five is greater than two!")
  

  • The print statement is indented to indicate it belongs to the if block.

Comments

• Comments are ignored by the interpreter and used for documentation.
• Single-line comment:

  # This is a comment
  

• Multi-line comment (using triple quotes):

  """
  This is a multi-line comment.
  It spans multiple lines.
  """
  

Variables and Data Types

Variables in Python are dynamically typed, meaning you don’t need to declare their type explicitly.

# Integer
age = 25

# Float
price = 19.99

# String
name = "Python"

# Boolean
is_student = True

In the Real World

Python is used extensively in Nepal and globally for automation, web services, and data processing. Here’s how some familiar platforms use Python:

1. eSewa (Nepal)

   • Use Case: Backend automation and API handling.
   • Python’s Role: Python scripts manage user transactions, payment processing, and database interactions. For example, when you pay a bill via eSewa, Python handles the validation of your payment details and updates the system records.

2. Khalti (Nepal)

   • Use Case: Payment gateway and fraud detection.
   • Python’s Role: Khalti uses Python for real-time transaction monitoring. If you transfer money to a friend, Python checks for suspicious activity (e.g., unusual transaction amounts) and flags it for review.

3. YouTube (Global)

   • Use Case: Recommendation algorithms and video processing.
   • Python’s Role: YouTube’s recommendation system uses Python to analyze user behavior (e.g., watch history, likes) and suggest videos. Python also processes video metadata (e.g., tags, captions) for indexing.

Writing a Simple Program: Calculating Compound Interest

Let’s write a program to calculate compound interest for a bank loan or investment, similar to how Ncell or Nabil Bank might compute interest for their customers.

Formula for Compound Interest

$$A=P{\left(1+\frac{r}{n}\right)}^{nt}$$ Where:

• $A$ = the future value of the investment/loan
• $P$ = principal amount (initial investment)
• $r$ = annual interest rate (decimal)
• $n$ = number of times interest is compounded per year
• $t$ = time the money is invested/borrowed for (in years)

Example: Nabil Bank Loan

Suppose you take a loan of NPR 500,000 at an annual interest rate of 8% (0.08), compounded monthly, for 5 years. Calculate the total amount to be repaid.

# compound_interest.py
principal = 500000
rate = 0.08
time = 5
compounds_per_year = 12

amount = principal * (1 + rate / compounds_per_year) ** (compounds_per_year * time)
print(f"Total amount to be repaid after {time} years: NPR {amount:.2f}")

Step-by-Step Execution

Output:

Total amount to be repaid after 5 years: NPR 745701.25

Python Keywords and Reserved Words

Python has a set of reserved keywords that cannot be used as variable names or identifiers. Examples include:

• if, else, elif
• for, while
• def, return
• class, import
• try, except

mindmap
  root((Python Keywords))
    if_else
      if
      else
      elif
    loops
      for
      while
    functions
      def
      return
    classes
      class
    exceptions
      try
      except
    imports
      import

Writing a Simple Program: Traffic Light Simulation

Let’s simulate a traffic light system for Kathmandu’s busy roads, where lights cycle through red, yellow, and green.

stateDiagram-v2
    [*] --> RED : Start
    state RED {
        [Stop] : 30 sec
    }
    RED --> GREEN : after 30 sec
    state GREEN {
        [Go] : 45 sec
    }
    GREEN --> YELLOW : after 45 sec
    state YELLOW {
        [Slow down] : 10 sec
    }
    YELLOW --> RED : after 10 sec

Traffic Light States

1. Red: Stop (30 seconds)
2. Yellow: Prepare to stop (5 seconds)
3. Green: Go (40 seconds)

Program Code

# traffic_light.py
import time

def traffic_light():
    states = ["Red", "Yellow", "Green"]
    durations = [30, 5, 40]  # in seconds

    for i in range(3):
        print(f"Light is {states[i]}")
        time.sleep(durations[i])  # Simulate time passing

traffic_light()

Step-by-Step Execution

Output:

Light is Red
[Waits 30 seconds]
Light is Yellow
[Waits 5 seconds]
Light is Green
[Waits 40 seconds]

Exam Tip

For the Tribhuvan University (TU) or Pokhara University (PU) exam, focus on the following key areas:

1. Python Basics: Understand the syntax, indentation, and basic structure of a Python program.
2. Environment Setup: Know how to install Python and use an IDE like IDLE or PyCharm.
3. First Program: Be able to write and run a simple program (e.g., printing a message or calculating a value).
4. Real-World Applications: Relate Python to everyday scenarios (e.g., banking interest, traffic systems, or e-commerce).
5. Error Handling: Recognize common errors (e.g., indentation errors, syntax errors) and how to fix them.

Common Exam Questions

• Write a Python program to print your name and age.
• Explain the difference between interpreted and compiled languages.
• What are Python keywords? Give 5 examples.
• How would you calculate compound interest in Python? Write a short program.
• Describe the steps to set up Python on your system.

Summary

• Python is a versatile, easy-to-learn programming language used in web development, data science, and automation.
• Setting up Python involves installing the interpreter and choosing an IDE (e.g., PyCharm, VS Code).
• Python programs use indentation for blocks and support dynamic typing.
• Real-world applications include eSewa transactions, Khalti payments, and YouTube recommendations.
• Practice writing small programs (e.g., compound interest, traffic light simulation) to reinforce concepts.