The Coder Bros — Master Modern Development

Code Cheatsheets

Search and browse syntax references for all supported languages. Copy code snippets with one click.

Variables

PythonBasics

Python variables are dynamically typed

name = "Alice"
age = 25
height = 1.75
is_student = True

Data Types

PythonBasics

Common Python data types

type(42)       # <class 'int'>
type(3.14)     # <class 'float'>
type("hello")  # <class 'str'>
type(True)     # <class 'bool'>
type([1,2,3])  # <class 'list'>

String Methods

PythonStrings

Common string operations

"hello".upper()        # HELLO
"HELLO".lower()        # hello
"  hi  ".strip()       # hi
"a,b,c".split(",")    # ['a','b','c']
"-".join(["a","b"])   # a-b

f-strings

PythonStrings

String interpolation

name = "Alice"
age = 25
print(f"{name} is {age} years old")
print(f"Pi = {3.14159:.2f}")

List Operations

PythonCollections

Common list methods

nums = [1, 2, 3]
nums.append(4)
nums.insert(0, 0)
nums.pop()
nums.sort()
[x*2 for x in nums]

Dict Operations

PythonCollections

Common dictionary methods

d = {"a": 1, "b": 2}
d["c"] = 3
d.get("x", 0)
d.keys()
d.values()
d.items()
{k: v*2 for k,v in d.items()}

Conditionals

PythonControl Flow

If-elif-else and ternary

if x > 0:
    print("positive")
elif x == 0:
    print("zero")
else:
    print("negative")

# Ternary
res = "even" if x % 2 == 0 else "odd"

Loops

PythonControl Flow

Loop patterns

for i in range(5):
for i, x in enumerate(lst):
for k, v in d.items():
while x > 0:

[x**2 for x in range(10) if x % 2 == 0]

Function Patterns

PythonFunctions

Function definition patterns

def add(a, b=0, *args, **kwargs):
    return a + b

# Lambda
square = lambda x: x**2

# Decorator
def timer(fn):
    def wrapper(*a, **kw):
        import time
        start = time.time()
        result = fn(*a, **kw)
        print(f"took {time.time()-start}s")
        return result
    return wrapper

Class Basics

PythonOOP

Class definition structure

class Dog:
    species = "Canine"
    def __init__(self, name):
        self.name = name
    def bark(self):
        return f"{self.name} says Woof!"

File Operations

PythonFile I/O

Reading and writing files

with open("file.txt", "r") as f:
    content = f.read()
    lines = f.readlines()
    for line in f:
        print(line.strip())

with open("file.txt", "w") as f:
    f.write("Hello\n")

Variables & Types

JavaScriptBasics

Variable declarations and type checking

let name = "Alice"
const age = 25
var old = "avoid"

typeof "hello"  // "string"
typeof 42       // "number"
typeof true     // "boolean"
typeof {}       // "object"
typeof []       // "object"

String Methods

JavaScriptStrings

String manipulation

"hello".toUpperCase()
"HELLO".toLowerCase()
"  hi  ".trim()
"a,b,c".split(",")
["a","b"].join("-")
`Hello, ${name}!`

Array Methods

JavaScriptArrays

Essential array operations

nums.push(4)
nums.pop()
nums.unshift(0)
nums.shift()
nums.slice(1,3)
nums.splice(1,1)
nums.map(x => x*2)
nums.filter(x => x > 2)
nums.reduce((a,b) => a+b, 0)

Arrow Functions

JavaScriptFunctions

Arrow function syntax

const add = (a, b) => a + b
const square = x => x * x
const greet = name => `Hello ${name}`

// Higher-order
const twice = fn => x => fn(fn(x))

Object Operations

JavaScriptObjects

Object manipulation

const user = { name: "Alice", age: 25 }
user.email = "a@b.com"
const { name, age } = user
const clone = { ...user }
Object.keys(user)
Object.values(user)
Object.entries(user)

Promises & Async/Await

JavaScriptAsync

Async patterns

fetch(url)
  .then(res => res.json())
  .catch(err => console.error(err))

async function getData() {
    try {
        const res = await fetch(url)
        return await res.json()
    } catch (err) {
        console.error(err)
    }
}

const [a, b] = await Promise.all([p1, p2])

DOM Manipulation

JavaScriptDOM

DOM selection and manipulation

document.querySelector('.class')
document.querySelectorAll('div')
elem.textContent = 'text'
elem.classList.add('active')
elem.style.color = '#D946EF'
elem.addEventListener('click', e => {
    console.log(e.target)
})

Document Structure

HTML/CSSHTML

Standard HTML5 template

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Page</title>
</head>
<body>
    <header>Nav</header>
    <main>Content</main>
    <footer>Footer</footer>
</body>
</html>

Flexbox

HTML/CSSCSS

Flexbox layout reference

.container {
    display: flex;
    justify-content: center;
    align-items: center;
    flex-wrap: wrap;
    gap: 1rem;
}

.item {
    flex: 1 1 200px;
}

Grid

HTML/CSSCSS

CSS Grid layout patterns

.grid {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 1rem;
}

.featured {
    grid-column: span 2;
}

.responsive {
    grid-template-columns: repeat(auto-fill, minmax(250px, 1fr));
}

Animations

HTML/CSSCSS

Transitions and keyframe animations

.element {
    transition: all 0.3s ease;
}

@keyframes slideIn {
    from { opacity: 0; transform: translateX(-20px); }
    to { opacity: 1; transform: translateX(0); }
}

Hello World

JavaBasics

Basic Java program structure

public class Hello {
    public static void main(String[] args) {
        System.out.println("Hello, World!");
    }
}

Collections & Streams

JavaCollections

Java Collections Framework

List<String> list = new ArrayList<>();
list.add("a");

Map<String, Integer> map = new HashMap<>();
map.put("a", 1);

list.stream()
    .filter(s -> s.startsWith("a"))
    .map(String::toUpperCase)
    .collect(Collectors.toList());

Hello World

C#Basics

Basic C# program

using System;

class Program {
    static void Main(string[] args) {
        Console.WriteLine("Hello, World!");
    }
}

LINQ Queries

C#LINQ

LINQ query and method syntax

var numbers = new[] { 1, 2, 3, 4, 5 };

var evens = from n in numbers
            where n % 2 == 0
            select n;

var squares = numbers
    .Where(n => n % 2 == 0)
    .Select(n => n * n);

Hello World

C++Basics

Basic C++ program

#include <iostream>

int main() {
    std::cout << "Hello, World!" << std::endl;
    return 0;
}

Pointers & References

C++Memory

Pointer and reference syntax

int value = 42;
int* ptr = &value;
int& ref = value;

*ptr = 100;

auto unique = std::make_unique<int>(42);
auto shared = std::make_shared<int>(100);

STL Containers

C++STL

STL algorithms and containers

#include <vector>
#include <algorithm>

std::vector<int> nums = {3, 1, 4, 1, 5};
std::sort(nums.begin(), nums.end());

auto it = std::find(nums.begin(), nums.end(), 4);

std::count_if(nums.begin(), nums.end(),
    [](int n) { return n % 2 == 0; });

def add(a, b=0, *args, **kwargs): return a + b # Lambda square = lambda x: x**2 # Decorator def timer(fn): def wrapper(*a, **kw): import time start = time.time() result = fn(*a, **kw) print(f"took {time.time()-start}s") return result return wrapper

fetch(url) .then(res => res.json()) .catch(err => console.error(err)) async function getData() { try { const res = await fetch(url) return await res.json() } catch (err) { console.error(err) } } const [a, b] = await Promise.all([p1, p2])

document.querySelector('.class') document.querySelectorAll('div') elem.textContent = 'text' elem.classList.add('active') elem.style.color = '#D946EF' elem.addEventListener('click', e => { console.log(e.target) })

<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <meta name="viewport" content="width=device-width, initial-scale=1.0"> <title>Page</title> </head> <body> <header>Nav</header> <main>Content</main> <footer>Footer</footer> </body> </html>

.grid { display: grid; grid-template-columns: repeat(3, 1fr); gap: 1rem; } .featured { grid-column: span 2; } .responsive { grid-template-columns: repeat(auto-fill, minmax(250px, 1fr)); }

List<String> list = new ArrayList<>(); list.add("a"); Map<String, Integer> map = new HashMap<>(); map.put("a", 1); list.stream() .filter(s -> s.startsWith("a")) .map(String::toUpperCase) .collect(Collectors.toList());

#include <vector> #include <algorithm> std::vector<int> nums = {3, 1, 4, 1, 5}; std::sort(nums.begin(), nums.end()); auto it = std::find(nums.begin(), nums.end(), 4); std::count_if(nums.begin(), nums.end(), [](int n) { return n % 2 == 0; });