Maksym

Posted on Aug 13

Python vs JavaScript Keywords Comparison

#python #javascript #beginners

Overview

Python has 35 keywords while JavaScript has 63+ reserved words (including future reserved words). Both languages use keywords to define syntax and control program flow, but they differ significantly in approach and philosophy.

Control Flow Comparison

Conditionals

Python	JavaScript	Notes
`if`	`if`	Same concept
`elif`	`else if`	Python uses single keyword, JS uses two words
`else`	`else`	Same

Python Example:

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

JavaScript Example:

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

Loops

Python	JavaScript	Notes
`for`	`for`	Different syntax, Python more intuitive
`while`	`while`	Similar concept
`break`	`break`	Same
`continue`	`continue`	Same
-	`do`	JS has do-while, Python doesn't

Python for loop:

for item in items:
    print(item)

for i in range(10):
    if i == 5:
        continue
    if i == 8:
        break

JavaScript for loop:

for (let item of items) {
    console.log(item);
}

for (let i = 0; i < 10; i++) {
    if (i === 5) continue;
    if (i === 8) break;
}

Functions & Classes

Python	JavaScript	Notes
`def`	`function`	Python shorter
`class`	`class`	Same (ES6+)
`return`	`return`	Same
`yield`	`yield`	Same (generators)
`lambda`	Arrow functions `=>`	Different syntax

Python:

def greet(name):
    return f"Hello, {name}"

# Lambda
square = lambda x: x ** 2

class Person:
    def __init__(self, name):
        self.name = name

JavaScript:

function greet(name) {
    return `Hello, ${name}`;
}

// Arrow function
const square = x => x ** 2;

class Person {
    constructor(name) {
        this.name = name;
    }
}

Variable Scope

Python	JavaScript	Notes
`global`	-	Python explicit global declaration
`nonlocal`	-	Python closure variable modification
-	`var`	JS function-scoped (legacy)
-	`let`	JS block-scoped
-	`const`	JS constant declaration

Python Scope:

x = 10  # global

def outer():
    x = 20  # local to outer

    def inner():
        global x  # refers to global x
        x = 30

        nonlocal x  # ERROR: can't use both
        # nonlocal would refer to outer's x

JavaScript Scope:

var x = 10;    // function-scoped
let y = 20;    // block-scoped  
const z = 30;  // constant

function example() {
    var a = 1;   // function-scoped
    let b = 2;   // block-scoped
    const c = 3; // constant

    if (true) {
        var a = 4;   // same 'a' as above
        let b = 5;   // different 'b'
        // const c = 6; // would shadow outer 'c'
    }
}

Exception Handling

Python	JavaScript	Notes
`try`	`try`	Same
`except`	`catch`	Different names
`finally`	`finally`	Same
`raise`	`throw`	Different names

Python:

try:
    result = 10 / 0
except ZeroDivisionError as e:
    print(f"Error: {e}")
except Exception as e:
    print(f"General error: {e}")
finally:
    print("Cleanup")

raise ValueError("Custom error")

JavaScript:

try {
    let result = 10 / 0;  // Returns Infinity, doesn't throw
    throw new Error("Custom error");
} catch (error) {
    console.log(`Error: ${error.message}`);
} finally {
    console.log("Cleanup");
}

Logical Operators

Python	JavaScript	Notes
`and`	`&&`	Python uses words
`or`	`\	\
{% raw %}`not`	`!`	Python uses word
`in`	`in`	Same for objects/arrays
`is`	`===`	Identity vs strict equality

Python:

if age >= 18 and has_license:
    can_drive = True

if name in users or is_admin:
    allow_access = True

if user is None:
    return "No user"

JavaScript:

if (age >= 18 && hasLicense) {
    canDrive = true;
}

if (name in users || isAdmin) {
    allowAccess = true;
}

if (user === null) {
    return "No user";
}

Unique to Each Language

Python-Only Keywords

elif - more concise than "else if"
pass - explicit no-operation
del - explicit object deletion
with - context managers
assert - built-in debugging
nonlocal - closure variable modification

JavaScript-Only Keywords

var, let, const - different variable declarations
switch, case, default - switch statements
do - do-while loops
new - object instantiation
this - context reference
typeof, instanceof - type checking
void - undefined operator
debugger - breakpoint statement

Async Programming

Python	JavaScript	Notes
`async`	`async`	Same (Python 3.5+)
`await`	`await`	Same

Python:

import asyncio

async def fetch_data():
    await asyncio.sleep(1)
    return "data"

async def main():
    result = await fetch_data()
    print(result)

JavaScript:

async function fetchData() {
    await new Promise(resolve => setTimeout(resolve, 1000));
    return "data";
}

async function main() {
    const result = await fetchData();
    console.log(result);
}

Key Philosophical Differences

Python Philosophy

Explicit is better than implicit - keywords like global, nonlocal
Readability counts - and, or, not instead of symbols
One way to do it - fewer keywords, more consistent

JavaScript Philosophy

Flexibility - multiple ways to declare variables (var, let, const)
C-style syntax - symbols over words (&&, ||, !)
Backward compatibility - keeps old keywords even when better alternatives exist