Programming Language Syntax

Quick side-by-side of common constructs across Python, JavaScript, Go, Rust, and more.

Reference Reference Updated Apr 19, 2026
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Variables & constants

Language Mutable var Immutable
Python x = 1 x: Final = 1
JavaScript let x = 1 const x = 1
TypeScript let x: number = 1 const x = 1 as const
Go var x int = 1 or x := 1 const x = 1
Rust let mut x = 1 let x = 1
Java int x = 1 final int x = 1
C# int x = 1 const int X = 1
Swift var x = 1 let x = 1

If / else

Language Syntax
Python if x > 0:\n ...\nelse:\n ...
JavaScript if (x > 0) { ... } else { ... }
Go if x > 0 { ... } else { ... }
Rust if x > 0 { ... } else { ... } (expression-valued)

For loop (range 0..n)

Language Syntax
Python for i in range(n):
JavaScript for (let i = 0; i < n; i++)
Go for i := 0; i < n; i++ { }
Rust for i in 0..n { }
Swift for i in 0..

Define a function (add two ints)

Language Syntax
Python def add(a: int, b: int) -> int:\n return a + b
JavaScript function add(a, b) { return a + b; }
TypeScript function add(a: number, b: number): number { return a + b; }
Go func Add(a, b int) int { return a + b }
Rust fn add(a: i32, b: i32) -> i32 { a + b }
Java static int add(int a, int b) { return a + b; }

String formatting

Language Syntax
Python f"Hello {name}, age {age}"
JavaScript `Hello ${name}, age ${age}`
Go fmt.Sprintf("Hello %s, age %d", name, age)
Rust format!("Hello {name}, age {age}")
Java String.format("Hello %s, age %d", name, age)
C# $"Hello {name}, age {age}"

Null / None

Python
None
JS / TS
null and undefined
Go
nil (pointer, interface, slice, map, chan, func)
Rust
Option::None — no null
Java / C#
null
Swift
Optional::nil

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