Modern JavasScript / Python Translation Guide

Are you familiar with JavaScript and looking for how to do something equivalent within Python?

(or vice versa?)

Python and JavaScript have many similar functionalities, but they are often called different things and have different consequences.

We're hoping to collect common types of requests and putting them here.

(Please note this is still in progress, pull requests welcome)

Try it out:

• Try it out with Python
• Try it out with JavaScript

Syntax

• Python Syntax reference - TODO
• JavaScript Syntax Reference - TODO

TOC

• Command Syntax
• Data Science Libraries

Command Syntax

Range

A range is a 1D array that progresses from a start number to an end number

Python:

print range(5)
# 0, 1, 2, 3, 4

JavaScript:

JavaScript doesn't have an equivalent and one is required to be made.

Note that number libraries like stdlib also can provide similar functionality

const 1dRange = (count) => Array.from(new Array(count), (x,i) => i));

idRange(5)
// [0,1,2,3,4]

Generators

Python

def foo():
    yield 1
    yield 2
    yield 3

JavaScript

function *foo() {
    yield 1;
    yield 2;
    yield 3;
}

Lambdas

Python

lambda a: a * 2

JavaScript

a => a * 2

Destructuring

Python

Note that Python allows for automatic destructuring using tuples.

status, data = getResult()

JavaScript

JavaScript allows destructuring for both object maps and arrays.

// getResult(): [number, number]

var [status, data] = getResult();
console.log(`status:${status}, data:${data}`)

or

// getObject(): {first, last}

var {first, last} = getObject();
console.log(`first:${first}, last:${last}`);

Spread Operators

search_db(**parameters)

searchDb(...parameters);

Iterators / Generators

Python

Generators

def fibonacci():
    pre, cur = 0, 1
    while True:
        pre, cur = cur, pre + cur
        yield cur

for x in fibonacci():
    if (x > 1000):
        break
    print x,

JavaScript

See MDN regarding iterators and generators

var fibonacci = {
  [Symbol.iterator]: function*() {
    var pre = 0, cur = 1;
    for (;;) {
      var temp = pre;
      pre = cur;
      cur += temp;
      yield cur;
    }
  }
}
for (var n of fibonacci) {
  if (n > 1000)
    break;
  console.log(n);
}

Classes

(Python has builtin support for multiple inheritance)

Python

class SpiderMan(Human, SuperHero):
    def __init__(self, age):
        super(SpiderMan, self).__init__(age)
        self.age = age
    def attack(self):
        print 'launch web'

JavaScript

class SpiderMan extends SuperHero {
    constructor(age) {
        super();
        this.age = age;
    }
    attack() {
        console.log('launch web')
    }
}

Comprehensions

names = [c.name for c in customers if c.admin]

JavaScript

They were proposed within JavaScript within EcmaScript v7, but were removed:

Quoting MDN:

The array comprehensions syntax is non-standard and removed starting with Firefox 58. For future-facing usages, consider using Array.prototype.map, Array.prototype.filter, arrow functions, and spread syntax.

(Experimental in Babel)

var names = [for (c of customers) if (c.admin) c.name];

Now using maps:

var names = customers.map(c => c.admin ? c.name : null);

Map

Python

double = lambda: x => x * 2
map(double, [1,2,3,4])
# [2,4,6,8]

JavaScript

const double = (x) => x * 2;
[1,2,3,4].map(double)
// [2,4,6,8]

string length

Python

 len([1,2,3,4])
 # 4

JavaScript

[1,2,3,4].length
# 4

Libraries

(In order of more common recommendations)

• Data Analysis Library
  • Python
    • pandas
  • Javascript - stack overflow
    • danfo-js
    • zebras
• DataFrame
  • Python
    • numpy
  • JavaScript - stack overflow
    • stdlib
    • tensorflow-js

Library Details

Pandas

What is it?

What is it useful for?

When is it not a good fit?

Considerations

If you're interested in this, try:

• Danfo-js

Danfo-js

What is it?

Built by the team at Tensorflow, one of the main goals of Danfo.js is to bring data processing, machine learning and AI tools to JavaScript developers.

Just like Pandas is built on top of Numpy, danfo-js is built on tensorflow-js

Danfo.js is heavily inspired by the Pandas library and provides a similar interface and API. This means users familiar with the Pandas API can easily use Danfo.js.

• Danfo.js is fast. It is built on Tensorflow.js, and supports tensors out of the box. This means you can convert danfo data structure to Tensors.
• Easy handling of missing data (represented as NaN) in floating point as well as non-floating point data
• Size mutability: columns can be inserted/deleted from DataFrame
• Automatic and explicit alignment: objects can be explicitly aligned to a set of labels, or the user can simply ignore the labels and let Series, DataFrame, etc. automatically align the data for you in computations
• Powerful, flexible groupby functionality to perform split-apply-combine operations on data sets, for both aggregating and transforming data
• Make it easy to convert Arrays, JSONs, List or Objects, Tensors and differently-indexed data structures into DataFrame objects
• Intelligent label-based slicing, fancy indexing, and querying of large data sets
• Intuitive merging and joining data sets
• Robust IO tools for loading data from flat-files (CSV and delimited) and JSON data format.
• Powerful, flexible and intutive API for plotting DataFrames and Series interactively.
• Timeseries-specific functionality: date range generation and date and time properties.
• Robust data preprocessing functions like OneHotEncoders, LabelEncoders, and scalers like StandardScaler and MinMaxScaler are supported on DataFrame and Series

What is it useful for?

When is it not a good fit?

Considerations

If you're interested in this, try:

Pandas-JS

Not Recommended - appears abandoned

Apache Arrow

What is it?

What is it useful for?

When is it not a good fit?

Considerations

MatPlotLib

What is it?

What is it useful for?

When is it not a good fit?

Considerations

If you're interested in this, try:

Vega-Lite

What is it?

What is it useful for?

When is it not a good fit?

Considerations

If you're interested in this, try:

TensorFlow

Library specification here

What is it?

What is it useful for?

When is it not a good fit?

Considerations

If you're interested in this, try:

TensorFlow-JS

What is it?

What is it useful for?

When is it not a good fit?

Considerations

If you're interested in this, try:

nltk

What is it?

What is it useful for?

When is it not a good fit?

Considerations

If you're interested in this, try:

numpy

What is it?

What is it useful for?

When is it not a good fit?

Considerations

If you're interested in this, try:

Zebras

What is it?

What is it useful for?

When is it not a good fit?

Considerations

If you're interested in this, try:

numjs

What is it?

What is it useful for?

When is it not a good fit?

Considerations

If you're interested in this, try:

D3

What is it?

What is it useful for?

When is it not a good fit?

Considerations

If you're interested in this, try:

natural

What is it?

What is it useful for?

When is it not a good fit?

Considerations

If you're interested in this, try:

scipy

What is it?

What is it useful for?

When is it not a good fit?

Considerations

If you're interested in this, try:

stdlib

What is it?

What is it useful for?

When is it not a good fit?

Considerations

If you're interested in this, try:

cython

What is it?

What is it useful for?

When is it not a good fit?

Considerations

If you're interested in this, try:

Multiprocessing

What is it?

What is it useful for?

When is it not a good fit?

Considerations

If you're interested in this, try:

ScramJet

What is it?

What is it useful for?

When is it not a good fit?

Considerations

If you're interested in this, try:

WebAssembly

What is it?

What is it useful for?

When is it not a good fit?

Considerations

If you're interested in this, try:

SymPy

What is it?

What is it useful for?

When is it not a good fit?

Considerations

If you're interested in this, try:

• MathJS
• Algebrite
• Pyodide

Jupyter Labs

What is it?

What is it useful for?

When is it not a good fit?

Considerations

If you're interested in this, try:

Jupyter Labs + IJavaScript

What is it?

What is it useful for?

When is it not a good fit?

Considerations

If you're interested in this, try:

Nteract

What is it?

What is it useful for?

When is it not a good fit?

Considerations

If you're interested in this, try:

Python Built-In BigInt

JavaScript Built-In BigInt