Modules and Packages

import _ from "lodash"; // whole module
import { sqrt } from "./mathUtils.js";  // a specific export
import * as utils from "./utils.js"; // namespace / alias

// --- Exporting (lib/print.js) ---
export function printLine() {
  console.log("hello world");
}
// or a barrel file (index.js) re-exporting:
//   export { printLine } from "./print.js";

// --- Relative imports use ./ and ../ ---
import { a } from "./sameFolder.js";
import { b } from "../parentFolder.js";
import { c } from "./folder1/folder2.js";

// Node.js ships with very little; 
// you install most utils from npm,
// so package.json tends to grow large.

import math  # whole module
from math import sqrt # a specific function
import math as m   # alias with `as`

print(math.sqrt(10))
print(sqrt(4))   # 2.0
print(m.sqrt(16)) # 4.0

# Best practice: 
# import only what you need (from module import thing),
# not the whole module 
# — same idea as JS named imports.

# --- Exporting: 
# a package is a folder with an __init__.py ---
# This is very similar to a React component's index.js barrel file.
#
#   lib/
#     __init__.py   <-- like index.js
#     print.py    <-- def print_line(): print("hello world")
#
# lib/__init__.py:
#     from .print import print_line  # relative import (leading dot)
#     __all__ = ["print_line"]  # controls what 
#                                `from lib import *` exposes
#
# workspace.py:
#     from lib import print_line
#     print_line()  # "hello world"

# --- Relative imports use dots, NOT slashes ---
#   from .print import x  # same folder  (JS: ./)
#   from ..parent import y # parent folder (JS: ../)
#   from .folder1.folder2 import z # subfolder (JS: ./folder1/folder2)

# Python is "batteries included" — 
# the standard library covers a huge amount,
# so you reach for pip far less often than npm.