Essential Python Packages for Every Developer

pip install xlsxwriter

import xlsxwriter

workbook  = xlsxwriter.Workbook('report.xlsx')
worksheet = workbook.add_worksheet('Sales')

# Add formatting
bold   = workbook.add_format({'bold': True, 'bg_color': '#4472C4', 'font_color': 'white'})
money  = workbook.add_format({'num_format': '$#,##0.00'})

# Write headers
headers = ['Product', 'Q1', 'Q2', 'Q3', 'Q4', 'Total']
for col, header in enumerate(headers):
    worksheet.write(0, col, header, bold)

# Write data
data = [
    ['Widget A', 1200, 1500, 1800, 2100],
    ['Widget B',  800,  950, 1100, 1300],
]

for row_num, row_data in enumerate(data, start=1):
    for col_num, value in enumerate(row_data):
        fmt = money if col_num > 0 else None
        worksheet.write(row_num, col_num, value, fmt)
    # Write SUM formula
    worksheet.write_formula(row_num, 5, f'=SUM(B{row_num+1}:E{row_num+1})', money)

workbook.close()
print("report.xlsx created")

pip install openpyxl

from openpyxl import load_workbook

wb = load_workbook('data.xlsx')
ws = wb.active

for row in ws.iter_rows(min_row=2, values_only=True):
    print(row)

pip install pandas

import pandas as pd

# Read CSV
df = pd.read_csv('sales.csv')

# Basic analysis
print(df.describe())
print(df.groupby('region')['revenue'].sum())

# Filter and transform
high_value = df[df['revenue'] > 10000].copy()
high_value['margin'] = high_value['revenue'] - high_value['cost']

# Export
high_value.to_excel('high_value_sales.xlsx', index=False)

pip install requests

import requests

# GET request
response = requests.get('https://api.example.com/users')
users = response.json()

# POST with JSON
response = requests.post(
    'https://api.example.com/users',
    json={'name': 'Alice', 'email': '[email protected]'},
    headers={'Authorization': 'Bearer mytoken'}
)

# Session for persistent connections
session = requests.Session()
session.headers.update({'Authorization': 'Bearer mytoken'})
response = session.get('https://api.example.com/data')

pip install httpx

import httpx
import asyncio

# Sync (same as requests)
with httpx.Client() as client:
    response = client.get('https://api.example.com/data')

# Async
async def fetch_all(urls):
    async with httpx.AsyncClient() as client:
        tasks = [client.get(url) for url in urls]
        responses = await asyncio.gather(*tasks)
        return [r.json() for r in responses]

pip install pymongo

from pymongo import MongoClient

client = MongoClient('mongodb://localhost:27017/')
db     = client['myapp']
users  = db['users']

# Insert
users.insert_one({'name': 'Alice', 'email': '[email protected]', 'active': True})

# Query
active_users = list(users.find({'active': True}, {'_id': 0, 'name': 1, 'email': 1}))

# Update
users.update_one({'email': '[email protected]'}, {'$set': {'role': 'admin'}})

# Delete
users.delete_one({'email': '[email protected]'})

pip install sqlalchemy

from sqlalchemy import create_engine, Column, Integer, String
from sqlalchemy.orm import DeclarativeBase, Session

class Base(DeclarativeBase):
    pass

class User(Base):
    __tablename__ = 'users'
    id    = Column(Integer, primary_key=True)
    name  = Column(String(100), nullable=False)
    email = Column(String(200), unique=True)

engine = create_engine('sqlite:///app.db')
Base.metadata.create_all(engine)

with Session(engine) as session:
    session.add(User(name='Alice', email='[email protected]'))
    session.commit()

    users = session.query(User).filter(User.name == 'Alice').all()

pip install click

import click

@click.group()
def cli():
    """My CLI tool."""
    pass

@cli.command()
@click.argument('name')
@click.option('--count', default=1, help='Number of greetings')
@click.option('--uppercase', is_flag=True, help='Uppercase output')
def greet(name, count, uppercase):
    """Greet someone."""
    for _ in range(count):
        msg = f"Hello, {name}!"
        click.echo(msg.upper() if uppercase else msg)

if __name__ == '__main__':
    cli()

python app.py greet Alice --count 3 --uppercase
# => HELLO, ALICE!
# => HELLO, ALICE!
# => HELLO, ALICE!

pip install rich

from rich.console import Console
from rich.table import Table
from rich.progress import track

console = Console()

# Styled output
console.print("[bold green]✓ Success[/bold green]")
console.print("[bold red]✗ Error:[/bold red] something went wrong")

# Table
table = Table(title="Users")
table.add_column("Name",  style="cyan")
table.add_column("Email", style="magenta")
table.add_column("Role",  style="green")

table.add_row("Alice", "[email protected]", "Admin")
table.add_row("Bob",   "[email protected]",   "User")

console.print(table)

# Progress bar
for item in track(range(100), description="Processing..."):
    pass  # do work

pip install python-dotenv

from dotenv import load_dotenv
import os

load_dotenv()  # loads .env file

DATABASE_URL = os.getenv('DATABASE_URL')
SECRET_KEY   = os.getenv('SECRET_KEY')
DEBUG        = os.getenv('DEBUG', 'false').lower() == 'true'

pip install pydantic

from pydantic import BaseModel, EmailStr, validator
from typing import Optional

class User(BaseModel):
    name:  str
    email: EmailStr
    age:   Optional[int] = None

    @validator('age')
    def age_must_be_positive(cls, v):
        if v is not None and v < 0:
            raise ValueError('Age must be positive')
        return v

# Validates automatically
user = User(name='Alice', email='[email protected]', age=30)
print(user.model_dump())

# Raises ValidationError on bad data
try:
    User(name='Bob', email='not-an-email')
except Exception as e:
    print(e)

pip install pytest

# test_math.py
def add(a, b):
    return a + b

def test_add():
    assert add(2, 3) == 5

def test_add_negative():
    assert add(-1, 1) == 0

def test_add_floats():
    assert add(0.1, 0.2) == pytest.approx(0.3)

pytest test_math.py -v

pip install faker

from faker import Faker

fake = Faker()

print(fake.name())           # => "John Smith"
print(fake.email())          # => "[email protected]"
print(fake.address())        # => "123 Main St, Springfield"
print(fake.phone_number())   # => "+1-555-123-4567"
print(fake.company())        # => "Acme Corp"
print(fake.text())           # => lorem ipsum paragraph

# Generate test dataset
users = [
    {'name': fake.name(), 'email': fake.email(), 'city': fake.city()}
    for _ in range(100)
]