Jeff Bruchado
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Python For JavaScript Developers: A Practical Transition Guide

Hello HaWkers, if you master JavaScript and want to expand your skills to Python, you're in the right place. With Python dominating areas like AI, data science and automation, adding this language to your arsenal has become practically mandatory in 2025.

Have you considered that much of what you know in JavaScript can be directly transferred to Python? Let's explore this transition in a practical and objective way.

Why Learn Python in 2025

The current market values polyglot developers. Python and JavaScript together cover virtually all areas of modern development.

Where Each Language Shines

JavaScript dominates:

  • Web frontend (React, Vue, Angular)
  • Backend with Node.js
  • Mobile applications (React Native)
  • Serverless and Edge Computing

Python dominates:

  • Machine Learning and AI
  • Data Science and data analysis
  • Automation and scripting
  • Scientific backend and data APIs

Both are strong:

  • REST and GraphQL APIs
  • Microservices
  • DevOps and automation

Basic Syntax Comparison

Let's start by comparing the fundamental structures of both languages.

Variables and Types

// JavaScript
const name = "Maria";
let age = 25;
var salary = 5000.50; // Avoid var

const list = [1, 2, 3];
const object = { name: "John", age: 30 };

// Dynamic typing
let value = 10;
value = "text"; // Valid, but not recommended
# Python
name = "Maria"
age = 25
salary = 5000.50

list = [1, 2, 3]
dictionary = {"name": "John", "age": 30}

# Similar dynamic typing
value = 10
value = "text"  # Valid

# Type hints (Python 3.9+)
name: str = "Maria"
age: int = 25
prices: list[float] = [10.5, 20.3, 15.0]

Functions

// JavaScript - Arrow functions
const sum = (a, b) => a + b;

// Traditional function
function calculateAverage(numbers) {
  const total = numbers.reduce((acc, n) => acc + n, 0);
  return total / numbers.length;
}

// Default parameters
const greet = (name, greeting = "Hello") => {
  return `${greeting}, ${name}!`;
};

// Destructuring in parameters
const processUser = ({ name, age }) => {
  console.log(`${name} is ${age} years old`);
};
# Python - Lambda (equivalent to arrow function)
sum = lambda a, b: a + b

# Traditional function
def calculate_average(numbers):
    total = sum(numbers)
    return total / len(numbers)

# Default parameters
def greet(name, greeting="Hello"):
    return f"{greeting}, {name}!"

# Unpacking in parameters
def process_user(user):
    name, age = user["name"], user["age"]
    print(f"{name} is {age} years old")

# Or with ** for kwargs
def process_user_v2(**user):
    print(f"{user['name']} is {user['age']} years old")

Control Structures

// JavaScript - Conditionals
const age = 18;

if (age >= 18) {
  console.log("Adult");
} else if (age >= 13) {
  console.log("Teenager");
} else {
  console.log("Child");
}

// Ternary
const status = age >= 18 ? "adult" : "minor";

// Switch
const day = 1;
switch (day) {
  case 1:
    console.log("Monday");
    break;
  case 2:
    console.log("Tuesday");
    break;
  default:
    console.log("Another day");
}
# Python - Conditionals
age = 18

if age >= 18:
    print("Adult")
elif age >= 13:
    print("Teenager")
else:
    print("Child")

# Ternary in Python
status = "adult" if age >= 18 else "minor"

# Match-case (Python 3.10+) - equivalent to switch
day = 1
match day:
    case 1:
        print("Monday")
    case 2:
        print("Tuesday")
    case _:
        print("Another day")

Loops

// JavaScript - Loops
const fruits = ["apple", "banana", "orange"];

// Traditional for
for (let i = 0; i < fruits.length; i++) {
  console.log(fruits[i]);
}

// For...of
for (const fruit of fruits) {
  console.log(fruit);
}

// forEach
fruits.forEach((fruit, index) => {
  console.log(`${index}: ${fruit}`);
});

// While
let counter = 0;
while (counter < 5) {
  console.log(counter);
  counter++;
}
# Python - Loops
fruits = ["apple", "banana", "orange"]

# For with range
for i in range(len(fruits)):
    print(fruits[i])

# Pythonic for (preferred)
for fruit in fruits:
    print(fruit)

# enumerate (equivalent to forEach with index)
for index, fruit in enumerate(fruits):
    print(f"{index}: {fruit}")

# While
counter = 0
while counter < 5:
    print(counter)
    counter += 1

Array vs List Manipulation

This is an area where the differences are more noticeable.

Array/List Methods

// JavaScript - Array methods
const numbers = [1, 2, 3, 4, 5];

// Map
const doubled = numbers.map(n => n * 2);
// [2, 4, 6, 8, 10]

// Filter
const evens = numbers.filter(n => n % 2 === 0);
// [2, 4]

// Reduce
const sum = numbers.reduce((acc, n) => acc + n, 0);
// 15

// Find
const firstGreaterThanThree = numbers.find(n => n > 3);
// 4

// Some and Every
const hasEven = numbers.some(n => n % 2 === 0);
// true
const allLessThanTen = numbers.every(n => n < 10);
// true

// Spread operator
const moreNumbers = [...numbers, 6, 7, 8];
# Python - List methods and functions
numbers = [1, 2, 3, 4, 5]

# Map (using list comprehension - more pythonic)
doubled = [n * 2 for n in numbers]
# [2, 4, 6, 8, 10]

# Or with map()
doubled_v2 = list(map(lambda n: n * 2, numbers))

# Filter (list comprehension)
evens = [n for n in numbers if n % 2 == 0]
# [2, 4]

# Or with filter()
evens_v2 = list(filter(lambda n: n % 2 == 0, numbers))

# Reduce
from functools import reduce
sum_result = reduce(lambda acc, n: acc + n, numbers, 0)
# 15

# Or simply
sum_v2 = sum(numbers)  # More pythonic

# Find (using next with generator)
first_greater_than_three = next((n for n in numbers if n > 3), None)
# 4

# Any and All (equivalents to some and every)
has_even = any(n % 2 == 0 for n in numbers)
# True
all_less_than_ten = all(n < 10 for n in numbers)
# True

# Spread equivalent
more_numbers = [*numbers, 6, 7, 8]

Asynchronous Programming

An area where JavaScript and Python have similar approaches, but with important differences.

Async/Await

// JavaScript - Async/Await
async function fetchUser(id) {
  try {
    const response = await fetch(`/api/users/${id}`);
    const user = await response.json();
    return user;
  } catch (error) {
    console.error("Error fetching user:", error);
    throw error;
  }
}

// Multiple promises in parallel
async function fetchData() {
  const [users, products] = await Promise.all([
    fetch("/api/users").then(r => r.json()),
    fetch("/api/products").then(r => r.json())
  ]);

  return { users, products };
}

// Execute
fetchUser(1).then(console.log);
# Python - Async/Await
import asyncio
import aiohttp

async def fetch_user(id):
    try:
        async with aiohttp.ClientSession() as session:
            async with session.get(f"/api/users/{id}") as response:
                user = await response.json()
                return user
    except Exception as error:
        print(f"Error fetching user: {error}")
        raise

# Multiple coroutines in parallel
async def fetch_data():
    async with aiohttp.ClientSession() as session:
        users_task = session.get("/api/users")
        products_task = session.get("/api/products")

        users_resp, products_resp = await asyncio.gather(
            users_task,
            products_task
        )

        users = await users_resp.json()
        products = await products_resp.json()

        return {"users": users, "products": products}

# Execute
asyncio.run(fetch_user(1))

Classes and Object-Oriented Programming

// JavaScript - Classes
class Animal {
  #name; // Private field

  constructor(name) {
    this.#name = name;
  }

  get name() {
    return this.#name;
  }

  speak() {
    console.log(`${this.#name} makes a sound`);
  }
}

class Dog extends Animal {
  constructor(name, breed) {
    super(name);
    this.breed = breed;
  }

  speak() {
    console.log(`${this.name} barks: Woof woof!`);
  }

  static createPuppy(name) {
    return new Dog(name, "Mixed");
  }
}

const rex = new Dog("Rex", "German Shepherd");
rex.speak();
# Python - Classes
class Animal:
    def __init__(self, name):
        self._name = name  # Private convention (underscore)

    @property
    def name(self):
        return self._name

    def speak(self):
        print(f"{self._name} makes a sound")


class Dog(Animal):
    def __init__(self, name, breed):
        super().__init__(name)
        self.breed = breed

    def speak(self):
        print(f"{self.name} barks: Woof woof!")

    @staticmethod
    def create_puppy(name):
        return Dog(name, "Mixed")


rex = Dog("Rex", "German Shepherd")
rex.speak()

Practical Tips For The Transition

Common Pitfalls

1. Indentation is mandatory in Python:

# This causes an error
if True:
print("hello")  # IndentationError!

# Correct
if True:
    print("hello")

2. No braces or semicolons:

# Don't do this
if (x > 5) {  # Syntax error
    print("greater")
};

# Do this instead
if x > 5:
    print("greater")

3. Lists are mutable by reference:

# Careful
original = [1, 2, 3]
copy = original  # Same reference!
copy.append(4)
print(original)  # [1, 2, 3, 4] - Modified original!

# Correct copy
real_copy = original.copy()
# or
real_copy = original[:]
# or
real_copy = list(original)

Tools and Environment

Recommended Setup

# Install Python (use pyenv to manage versions)
curl https://pyenv.run | bash
pyenv install 3.12
pyenv global 3.12

# Create virtual environment (equivalent to node_modules)
python -m venv venv
source venv/bin/activate  # Linux/Mac
# or
.\venv\Scripts\activate  # Windows

# Install dependencies
pip install requests flask pandas

# Save dependencies (equivalent to package.json)
pip freeze > requirements.txt

# Install from requirements.txt
pip install -r requirements.txt

Equivalent Tools

JavaScript Python
npm/yarn/pnpm pip/poetry/pipenv
package.json requirements.txt/pyproject.toml
node_modules venv/virtualenv
ESLint Pylint/Ruff/Flake8
Prettier Black/Autopep8
Jest/Vitest Pytest
Express Flask/FastAPI

Conclusion

The transition from JavaScript to Python is smoother than it seems. The fundamental concepts are the same, only the syntax changes. The key is to:

  • Embrace the pythonic style (list comprehensions, formatting)
  • Understand the differences in scope and reference
  • Practice with real projects

In 2025, mastering both languages opens doors to virtually any area of development. JavaScript for web and mobile, Python for AI and data. Together, they form an unbeatable combination.

If you want to continue expanding your skills, I recommend checking out another article: Developer Market in 2025 where you'll discover which skills are in high demand.

Let's go! 🦅

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