# my_package/module1.py
def greet():
    return "Hello from module1"

# main.py
import my_package.module1

print(my_package.module1.greet())

import os

os.mkdir("new_folder")
os.makedirs("parent/child/grandchild")

# file: calculator.py
def multiply(a, b):
    return a * b

# main.py
import calculator

print(calculator.multiply(4, 5))  # Output: 20

with open("sample.txt", "w") as file:
    file.write("Hello, Python File System")

class NegativeNumberError(Exception):
    pass

def check_number(n):
    if n < 0:
        raise NegativeNumberError("Negative numbers are not allowed")

check_number(-3)

---------------------------------------------------------------------------

NegativeNumberError                       Traceback (most recent call last)

Cell In[1], line 8
      5     if n < 0:
      6         raise NegativeNumberError("Negative numbers are not allowed")
----> 8 check_number(-3)


Cell In[1], line 6 …

class ApplicationError(Exception):
    pass

class DatabaseError(ApplicationError):
    pass

class NetworkError(ApplicationError):
    pass

class Car:
    def __init__(self, brand):
        self.brand = brand

c1 = Car("Toyota")
c2 = Car("Tesla")

print(c1.brand)
print(c2.brand)

Toyota
Tesla

import csv

with open("custom.csv", "w", newline="") as file:
    writer = csv.writer(file, delimiter="|")
    writer.writerow(["Name", "Age", "Country"])
    writer.writerow(["Alice", 25, "India"])

class InvalidAgeError(Exception):
    pass

def validate_age(age):
    if age < 18:
        raise InvalidAgeError("Age must be 18 or above")

try:
    validate_age(16)
except InvalidAgeError as e:
    print(e)

Age must be 18 or above

class TransactionError(Exception):
    def __init__(self, code, message):
        self.code = code
        self.message = message
        super().__init__(f"[{code}] {message}")

raise TransactionError(403, "Unauthorized action")