Python Tutorial

Python Tutorial: From Beginner to Intermediate

This tutorial covers the fundamentals of Python, including syntax basics, data structures, control flow, and advanced topics for experienced programmers.

1. Getting Started

What is Python?

Python is a high-level programming language known for its simplicity and readability.

• Why learn Python?
  • Easy to read and write code (less boilerplate).
  • Extensive standard library for built-in functions.
  • Supports multiple programming paradigms (procedural, object-oriented, functional).

Installing Python

1. Download from Python Official Website.
2. On Windows: Run the installer and choose MSI installation.
3. For Linux/MacOSX: Use your package manager to install Python.

---

2. Basic Syntax

Variables

In Python, variables are declared without explicit declaration (no need for var() or int()).

# Example:
x = "Hello"
y = 5
z = True  # Boolean type

Comments

• Single-line comment: # This is a comment
• Multi-line comment using triple quotes:

"""
This is a multi-line comment.
It can span multiple lines and still be readable.
"""

---

3. Data Structures

Numbers (ints, floats)

Python supports integers (int) and floating-point numbers (float).

a = 10   # int  
b = 5.67  # float  
c = True  # Boolean type is a subclass of int in Python

Strings

Strings are sequences of characters enclosed in quotes.

s = "Hello, World!"  # Double-quoted strings recommended for readability.
print(s)            # Outputs: Hello, World!

Lists and Tuples

Lists

A list is an ordered collection of elements:

my_list = [10, 20.5, True]  
print(my_list[0])          # Outputs: 10  
print(len(my_list))        # Outputs: 3 (since it's mutable)

Tuples

A tuple is similar to a list but immutable:

my_tuple = ("Hello", "World") 
# Cannot change the elements of a tuple after creation.

Sets and Dictionaries

Sets

An unordered collection of unique elements.

s = {1, 2, 3}  
if 2 in s:
    print("Element found!")  
else:  
    print("Element not present.")

Dictionaries

A dictionary stores key-value pairs:

d = {"key": "value", ("another key"): None}
print(d["key"])   # Outputs: value
# Note: Keys must be immutable types (e.g., strings, numbers).

---

4. Control Flow

Conditional Statements

Use if, elif, and else statements.

x = 10  
y = 5  

if x > y:
    print("x is greater than y.")
elif x == y: 
    print("x equals y.")
else:
    print(f"Wait, {x} can't be less than a positive number like {y}.")

Loops

Python supports for and while loops.

For Loop

# Iterate over elements in an iterable (e.g., list):
my_list = [10, 20.5, True]  
for item in my_list:
    print(item)
print("Loop completed.")

While Loop

count = 0  

while count < 3: 
    print(f"Count is {count}")
    count += 1
# Outputs:
# Count is 0
# Count is 1
# Count is 2  

---

5. Functions and OOP (Object-Oriented Programming)

Defining a Function

def greet(name):
    """Returns a greeting message."""
    return f"Hello, {name}!"

print(greet("Alice"))   # Outputs: Hello, Alice!

Classes in Python

Example of a Simple Class:

class Rectangle:
    def __init__(self, length, width):  
        self.length = length  # Instance variable
        self.width = width
    
    def area(self):
        """Returns the area of the rectangle."""
        return self.length * self.width  

# Creating an instance:
r1 = Rectangle(2.0, 3.5)  
print(r1.area())   # Outputs: 7.0

---

6. Advanced Topics

Error Handling (Exception Handling)

try:
    x = int(input("Enter a number: ")) 
except ValueError:
    print("Please enter a valid integer.")
else:
    y = float(x)
    z = y / 2  
    print(f"The half of {x} is {z}.")

Lambda Functions

# Example lambda function that adds two numbers:
add = lambda x, y: x + y  

print(add(3,5))   # Outputs: 8

---

7. File Handling

Reading and writing files in Python:

# Reading a file line by line:
file_name = "data.txt"  
with open(file_name, 'r') as f:
    for line in f:
        print(line.strip())
        
# Writing to a new file (note: mode is read-write):
with open("new_file.txt", 'w') as f:
    f.write("Hello from Python!")

---

8. Modules and Packages

Importing Modules

import math  
print(math.sqrt(25))   # Outputs: 5.0  

# Using a module's function without importing the entire module (optional):
sqrt_16 = lambda x=4: math.sqrt(x)
print(sqrt_16())    # Outputs: 2.0

from math import sqrt as m_sqrt  
print(m_sqrt(9))     # Outputs: 3.0

Installing Packages via pip

pip install numpy  
import numpy as np  
arr = np.array([1,2,3]) 
print(arr)   # Outputs: [1 2 3]

---