Code Compare

Side-by-side syntax "comparisons" between 3 languages: Python (3), JavaScript(ES6) and Ruby

Note: not every data type or function has a direct comparison in the other language, sometimes these are approximate.

Operation	Python	JS (ES6)
print	print("Hello world!")	console.log('Hello World!')
functions	def myfunction():    print("running")	function myFunction()    { code here }
calling functions	my_function()	myFunction()
conditionals	if condition:    do sthing else:    do sthing else	if (condition) {     statement } else {    statement }
inline conditional	val_when_true if condition else val_when_false	{ condition? 'true':'false'}
safe navigation operator	not yet	obj.value?.property

In-depth comparison

Conditionals

Function	Python	JS (ES6)	Notes
Conditionals	if, elif, else	if, else if, else	-
Ternary operators	val_when_true if condition else val_when_false	{ condition? 'true':'false'}
Switch/case	-	switch case expression when condn    statement

Comparison (equal/not equal) and Boolean (and/or/not) operators

Operator	Python	JS (ES6)	Notes
Boolean	bool(var)	var.length
Falsey	0, 0.0, ''		false, nil
Equal to	==	==/===	==
Not equal to	!=	!=/!==	!=
And	and	&&	&&
Or	or	||	||
Not	not	!	! / unless?

Functions

Python	JS (ES6)	Notes
def myfunction(args)	function myFunction() { //code here }	JS functions and vars are defined using camelCase
JS Arrow func. syntax =>	const myFunction = () => { // code here }	const myFunction = (args) => { // code here }
JS Arrow func syntax allows for single-line function definition	If returning a JS object wrap it in ( )	=> ({JS object})

Loops

Operator	Python	JS (ES6)	Notes
For	for i in range(x):	-	For loops iterate a specific no. of times
While	while i < 3:``while True:	-	While loops iterate while a certain condn is true

Built-in functions e.g. length

Function	Python	JS (ES6)	Notes
string	str(var)		-
int	int(var)		-
length	len(var)		-
type	type(var)	typeof(var)	-
user input	input("")	window.prompt("")	input is always a str by default
F and template strings	f strings: f"Hello, {var}"	Hello, ${name}	whitespace is honoured in both
Sleep (delay)	sleep(5)	setTimeout(myFunc, 2000)	where 2000 is in ms

Data structures

Data type	Python	JS (ES6)	Notes
String	"string" or 'string'		-
Integer	1		-
Boolean	True		-
Mutable List	[1,2,3]		-
Unmutable list	tuple (1,2,3)		-
Key:value	Dictionary {"key":"value"}	JS Object	-

Web development framework comparison

X	Python	JS (ES6)	Ruby
Web development frameworks	Flask, Django	React, Vue, Angular, NextJS	Sinatra, Ruby on Rails
Unit testing	Pytest, Unitttest	Jest (test runner) + React testing library/Cypress ]	RSpec, minitest
Syntax linting	pylint	ESLint	Rubocop
Frontend tests	Selenium	Cypress	Capybara, Cucumber

X	Python - Django	React JS	Ruby on Rails
Package manager	pip, pipenv, poetry	node, yarn	RubyGems => bundler
Package config stored in:	requirements.txt	package.json/yarn.lock	Gemfile.lock
Library installation	pip install <lib>	npm/yarn install <package>	gem install <gem>
Library/package import	import library	import library / { Component } from	require "package"

Frontend

Displaying variables

Framework	Syntax name	Example	Notes
Django	Jinja2	<p>{{ person.name }}</p>	-
ReactJS	JSX/ JS expression	<p>{personName}</p>	JSX is not readable by the browser, hence uses Babel

Language specific syntax

React Javascript

JSX is not HTML but a combination of JS + XML

React component syntax

<Component prop={} />

<ParentComponent>
 <ChildComponent>
</ParentComponent>

Object destructuring in React component props

Version	React component	props usage	Notes
v1 using props	export default function Menu(props) {..	<p>{props.title}</p>
v2 destructured	export default function Menu({title, recipe}) {..	<p>{title}</p>

Python

Scope

Think of scope as a container

Local scope is temporary, created when a function is called and destroyed when the function returns. A local variable cannot be used in a global scope.

Global scopes are created outside a function

This allows functions to work as individual black boxes and helps isolate code.

variable = 'GLOBAL'

def my_function():
    variable = 'local'

Q In the below, what value of name will be printed out?

def func_1():
    name = 'Maria'
    func_2()
    print(name)
    
def func_2():
    name = 'Bob'

func_1()

Answer

Maria - as the scope of func_2 will be destroyed once it returns

The global keyword can be used to create global variables in a local context (within a function)

Q What will be the output if you run the below?

result = 0 # initial global variable

def add():
    global result
    result = result + 2 # increment by 2
    print("Inside add():", result)

add()
print("In main:", result)

Answer

When we run the above script, the output will be: Inside add(): 2 In main: 2

Q In a python function without a return statement, what type does the return value default to?

Answer

NoneType

Standard if/else blocks keep the existing scope and don't destroy them like a function.

Q In the below, what value of number will be printed out?

number = 9

if True:
 number = 15

print(number)

Answer

if True means that the indented code underneath will always be executed, 15 - if/else statements do not convert code to local scope, they mantain the existing scope.

Args and Kwargs

Q What are the kwargs (optional args) for the print() function?

Answer

sep='sthing to separate each str by', end="" <--no /n after each print() call```

print("a string", sep=, end=)

def myfunction(arg1, arg2=defaultvalue):
    print("hi")
myfunction(2,3)

Q What wil be the output of the below code snippet? #TODO

def myfunction(arg1, arg2=99):
    print(arg1,arg2)
myfunction(2,3)

Answer

2, 3  as those values will have overridden the default

For Loops

Q how many times will this sentence be printed?

for i in range(3):
    print('hi')

Answer

3 times, the first time the variable i is set to 0, then 1 and 2 not including 3. Total of 3 times - as range(3)

Q Write a for loop to count the sum of all no.s from 1 to 100

Answer

total = 0
for i in range(101):
    total = total + i
print(total)

Q Sum of all no.s from 4 to 99

Answer

total = 0
for i in range(4, 100):
    total = total + i
print(total)

To append items to a list in a for loop, remember to instantiate your list outside the for loop

Functions from built-in modules e.g. random, sys

Remember all python functions have a return value, if no return statement, the return value defaults to a None type.

Getting arguments from the command line import sys

Q What is sys.argv[0] in the following line? python myscript.py jenna 2

Answer

myscript.py
sys.argv[0] is the name of the script being run, with the following arguments being sys.argv[1] and [2] and so on

Q What is the type of any arguments passed in to a python script by default? thourgh sys or input()?

Answer

string
that's why for integers you must specify input = int(.... or int(sys.argv[1])

Python dunder methods

Method	Description	Use	?
__main__	A module’s name is set equal to 'main' when read from standard input	if __name__ == __main__:	..
__file__	returns the path specified (usually the filepath)	filepath = __file__	..
__init__	object inittialisation	def __init__(self,	..

Python string methods

Method	Description	Use	?
strip()	remove whitespace at start and end of a string	myvar.strip()	..
replace()	specified value is replaced by another	myvar.replace(" ","")	..
join()	useful for converting iterables to strings	separator.join(iterable)	..

Python number/integer methods

Method	Description	Example	Use
filter()	takes a function and an iterable as arguments and constructs a new iterable by applying the function to every element in the list	filter even no.s	even = filter(lambda x: x % 2 == 0, integers)
map()	applies a function to every element in a list. Unlike filter, it leaves the number of elements in the list unchanged	myvar.replace(" ","")	..
reduce()	Reduce works by applying a function that takes two arguments to the elements in the list, from left to right	..	..

Python list comprehensions

Module	usage	example	notes
random	random.randint(var)	random.randint(1,10)	generate random number between 1 and 10
sys	sys.exit()	sys.exit()	This allows a script to terminate, anything below this code will not be ecxecuted
get even no.s	even = [x for x in integers if x % 2 == 0]	bla

JavaScript (ES6)

Defining variables

New let, const keywords were introduced. Unlike let variables, const variables cannot be changed.

let x = 2;
const company = 'BT'

Object destructuring

Ruby

Symbols ( : )

• An immutable data type
• Symbols are denoted by a colon (:) and are identifiers (fixed values) unlike strings which are meant to be mutable,
• Tend to be used for method names or attribute names

my_symbol = :name
my_symbol2 = :name

my_symbol.object_id and my_symbol2.object_id will be the same

Hashes

• Hashes are as objects in JS

Unit tests - RSpec

describe "scenario name" do
  it "test name" do
    <test code here>
    <expectation here>
  end
  
  decribe "can create a new country" do
   it "create country" do