Python

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

History of Python

• Late 1980s – Developed by Guido van Rossum at Centrum Wiskunde & Informatica (CWI), Netherlands.
• 1991 – First public release: Python 0.9.0, which already included modules, exceptions, functions, and core data types (str, list, dict).
• Named after the British comedy series “Monty Python’s Flying Circus”, not the snake.

Major Python Versions & Key Features

Python 1.x (1991 – 2000)

• First stable release: Python 1.0 (1994).
• Key features: functions, exceptions, core data types, and modules.
• Early focus on extensibility and portability.

Python 2.x (2000 – 2020)

• Released in 2000 with many improvements, but also some design flaws.

• Major features:

  • List comprehensions.
  • Garbage collection via reference counting & cycles.
  • Unicode support (limited in 2.x).

• Python 2.7 (2010) became the last release in the 2.x line.

• Official support ended on January 1, 2020.

Python 3.x (2008 – present)

• Released in 2008, not backward-compatible with Python 2.

• Major features and changes:

  • print() function replaces print statement.
  • Unicode by default (all strings are Unicode).
  • Integer division change: / gives float, // gives integer.
  • Function annotations for better readability and typing support.
  • Async/await keywords (introduced in Python 3.5).
  • F-strings (formatted string literals, introduced in 3.6).
  • Type hinting improvements (gradually added).
  • Pattern matching (introduced in 3.10).
  • Performance optimizations (especially in Python 3.11+).

Features

1. Print as a Function

# Python 3
print("Hello, World!")

# Python 2 (invalid in Python 3)
# print "Hello, World!"

2. Unicode by Default

text = "こんにちは"  # Japanese for "Hello"
print(text)  # Strings are Unicode by default in Python 3

3. Integer Division Change

print(5 / 2)   # 2.5  (float division)
print(5 // 2)  # 2    (integer division)

4. Function Annotations / Type Hints

def greet(name: str, age: int) -> str:
    return f"Hello, {name}. You are {age} years old."

print(greet("Alice", 25))

5. Generators with yield

def count_up_to(n):
    i = 1
    while i <= n:
        yield i  # Produces values one at a time
        i += 1

for number in count_up_to(5):
    print(number)

6. Async / Await (Asynchronous Programming)

import asyncio

async def say_hello():
    await asyncio.sleep(1)
    print("Hello after 1 second")

asyncio.run(say_hello())

7. F-Strings (Formatted String Literals)

name = "Alice"
age = 25
print(f"My name is {name} and I am {age} years old.")

8. Improved Iteration with enumerate and zip

fruits = ["apple", "banana", "cherry"]

for i, fruit in enumerate(fruits, start=1):
    print(i, fruit)

colors = ["red", "yellow", "purple"]
for fruit, color in zip(fruits, colors):
    print(f"{fruit} is {color}")

9. Unpacking in Assignments

a, b, *rest = [1, 2, 3, 4, 5]
print(a, b, rest)  # 1 2 [3, 4, 5]

10. Pattern Matching (Python 3.10+)

def match_example(value):
    match value:
        case 0:
            return "Zero"
        case 1 | 2:
            return "One or Two"
        case _:
            return "Something else"

print(match_example(2))   # One or Two

11. Walrus Operator (:=, Python 3.8+)

# Assignment inside expression
if (n := len("Python")) > 3:
    print(f"Length is {n}")

12. Dictionary Comprehensions

squares = {x: x*x for x in range(5)}
print(squares)  # {0: 0, 1: 1, 2: 4, 3: 9, 4: 16}

13. Set Comprehensions

unique = {x for x in "banana"}
print(unique)  # {'a', 'n', 'b'}

14. Context Managers (with)

with open("example.txt", "w") as f:
    f.write("Hello, file!")

15. Exception Handling with as

try:
    1 / 0
except ZeroDivisionError as e:
    print("Error:", e)

16. Extended Iterable Unpacking (PEP 3132)

first, *middle, last = [1, 2, 3, 4, 5]
print(first, middle, last)  # 1 [2, 3, 4] 5

17. Named Expressions in Loops

data = ["apple", "banana", "cherry"]
while (item := data.pop(0)) != "cherry":
    print(item)

18. Improved Performance in Recent Versions (3.11+)

Try running the following with older versions and with versions with 3.11+:

import time

# Example 1: Function calls (faster in 3.11+)
def add(a, b):
    return a + b

def benchmark_func_calls(n=10_000_00):
    for _ in range(n):
        add(1, 2)

# Example 2: Exception handling (optimized in 3.11+)
def benchmark_exceptions(n=100_000):
    for _ in range(n):
        try:
            raise ValueError("test")
        except ValueError:
            pass

# Example 3: Nested loops (general interpreter speedup)
def benchmark_loops(n=1_000_000):
    s = 0
    for i in range(n):
        s += i
    return s

# Run benchmarks
start = time.time()
benchmark_func_calls()
print("Function calls:", time.time() - start, "seconds")

start = time.time()
benchmark_exceptions()
print("Exceptions:", time.time() - start, "seconds")

start = time.time()
benchmark_loops()
print("Loops:", time.time() - start, "seconds")

List comprehensions

1. Square numbers

squares = [x*x for x in range(5)]
print(squares)  # [0, 1, 4, 9, 16]

---

2. Filtering with a condition

evens = [x for x in range(10) if x % 2 == 0]
print(evens)  # [0, 2, 4, 6, 8]

---

3. Applying a function

words = ["hello", "world", "python"]
uppercased = [w.upper() for w in words]
print(uppercased)  # ['HELLO', 'WORLD', 'PYTHON']

4. Cartesian product

pairs = [(x, y) for x in [1, 2] for y in [3, 4]]
print(pairs)  # [(1, 3), (1, 4), (2, 3), (2, 4)]

---

5. Flatten a matrix

matrix = [[1, 2], [3, 4], [5, 6]]
flattened = [num for row in matrix for num in row]
print(flattened)  # [1, 2, 3, 4, 5, 6]

6. Inline if-else

labels = ["even" if x % 2 == 0 else "odd" for x in range(5)]
print(labels)  # ['even', 'odd', 'even', 'odd', 'even']

---

7. Remove vowels from a string

text = "comprehension"
no_vowels = [ch for ch in text if ch not in "aeiou"]
print(no_vowels)  # ['c', 'm', 'p', 'r', 'h', 'n', 's', 'n']

---

8. Transpose a matrix

matrix = [[1, 2, 3], [4, 5, 6]]
transpose = [[row[i] for row in matrix] for i in range(3)]
print(transpose)  # [[1, 4], [2, 5], [3, 6]]

---

9. Set and Dictionary Comprehensions (related feature)

# Set comprehension
unique = {x % 3 for x in range(10)}
print(unique)  # {0, 1, 2}

# Dict comprehension
squares_dict = {x: x*x for x in range(5)}
print(squares_dict)  # {0: 0, 1: 1, 2: 4, 3: 9, 4: 16}

Advanced Features

1. Decorators (Functions that modify other functions/classes)

def debug(func):
    def wrapper(*args, **kwargs):
        print(f"Calling {func.__name__} with {args} {kwargs}")
        return func(*args, **kwargs)
    return wrapper

@debug
def greet(name):
    return f"Hello, {name}"

print(greet("Alice"))

2. Generators and yield (Lazy evaluation, efficient iteration)

def fibonacci(n):
    a, b = 0, 1
    for _ in range(n):
        yield a
        a, b = b, a + b

print(list(fibonacci(10)))

3. Context Managers (with) & __enter__ / __exit__

class ManagedFile:
    def __init__(self, filename):
        self.filename = filename
    
    def __enter__(self):
        self.file = open(self.filename, "w")
        return self.file
    
    def __exit__(self, exc_type, exc_value, traceback):
        self.file.close()

with ManagedFile("test.txt") as f:
    f.write("Hello, world!")

4. Metaclasses (Classes that create classes)

class Meta(type):
    def __new__(cls, name, bases, dct):
        print(f"Creating class {name}")
        return super().__new__(cls, name, bases, dct)

class MyClass(metaclass=Meta):
    pass

5. Descriptors (Custom attribute access)

class Celsius:
    def __get__(self, instance, owner):
        return instance._celsius
    def __set__(self, instance, value):
        if value < -273.15:
            raise ValueError("Temperature below absolute zero!")
        instance._celsius = value

class Temperature:
    celsius = Celsius()

t = Temperature()
t.celsius = 25
print(t.celsius)  # 25

6. Coroutines (async / await)

import asyncio

async def main():
    await asyncio.sleep(1)
    print("Done after 1 second")

asyncio.run(main())

7. Pattern Matching (Python 3.10+)

def handle(data):
    match data:
        case {"type": "error", "msg": msg}:
            print(f"Error: {msg}")
        case {"type": "success", "value": v}:
            print(f"Success: {v}")
        case _:
            print("Unknown")

handle({"type": "error", "msg": "File not found"})

8. Multiple Inheritance & MRO (Method Resolution Order)

class A: 
    def hello(self): print("A")
class B(A): 
    def hello(self): print("B")
class C(A): 
    def hello(self): print("C")
class D(B, C): 
    pass

D().hello()        # B (follows MRO: D → B → C → A)
print(D.mro())     # Method Resolution Order

9. Dynamic Code Execution (eval, exec)

code = "x = 5\ny = 10\nprint(x + y)"
exec(code)   # Runs dynamically

10. Property Decorator (@property)

class Circle:
    def __init__(self, radius):
        self._radius = radius
    
    @property
    def area(self):
        return 3.14 * self._radius ** 2

c = Circle(5)
print(c.area)  # 78.5

11. Monkey Patching (Changing behavior at runtime)

class Person:
    def say_hello(self):
        print("Hello!")

def new_hello(self):
    print("Hi there!")

Person.say_hello = new_hello
p = Person()
p.say_hello()  # Hi there!

12. Closures (Functions inside functions)

def multiplier(factor):
    def inner(x):
        return x * factor
    return inner

double = multiplier(2)
print(double(5))  # 10

13. Slots (__slots__) for Memory Optimization

class Point:
    __slots__ = ("x", "y")  # Prevents dict overhead
    def __init__(self, x, y):
        self.x, self.y = x, y

p = Point(1, 2)
print(p.x, p.y)

14. Operator Overloading (__add__, __str__, etc.)

class Vector:
    def __init__(self, x, y):
        self.x, self.y = x, y
    
    def __add__(self, other):
        return Vector(self.x + other.x, self.y + other.y)
    
    def __str__(self):
        return f"({self.x}, {self.y})"

v1 = Vector(1, 2)
v2 = Vector(3, 4)
print(v1 + v2)  # (4, 6)