Python.v.JavaScript

JavaScript for Pythonistas. Python for JavaScripters

Dicts / objects

The standard structure to store elements accessible by arbitrary keys (mapping) in Python is called a dict (dictionary) and in JavaScript — object.

Python Javascript

Python	Javascript
Creation of dictionary / object #
`my_dict = {'a': 10, 'b': 20} my_dict['a']` 10 `my_dict.a` Exception: AttributeError 'dict' object has no attribute 'a'	`var my_obj = {a: 10, b: 20};my_obj['a'];` 10 `my_obj.a;` 10 You can access elements of an object either with square brackets or with dot-notation. `var my_obj = {'long key': 'some value', short_key: 'other value'}my_obj['long key'];` some value `my_obj['short_key'];` other value `my_obj.short_key;` other value
Modification of a value in dictionary / object #
`my_dict = {'a': 10, 'b': 20} my_dict['a'] = 'hello' my_dict['a']` 'hello'	`var my_obj = {a: 10, b: 20}; my_obj['a'] = 'hello';my_obj['a'];` hello `var my_obj = {a: 10, b: 20}; my_obj.a = 'hello';my_obj['a'];` hello Two ways of access (square brackets and dot-notation) gives the same element.
Non-string keys #
`my_dict = {} my_dict[5] = 'hello' my_dict['5'] = 'world' my_dict` {5: 'hello', '5': 'world'}	`var my_obj = {}; my_obj[5] = 'hello'; my_obj['5'] = 'world';my_obj;` { '5': 'world' } `my_obj[ ['5'] ];` world Keys of elements in JavaScript object has to be string. Any other key will be coerced to string.
Check if element with given key exists #
`my_dict = {'a': 10, 'b': 20} 'a' in my_dict` True	`my_obj = {a: 10, b: 20};'a' in my_obj;` true
Access to non-existent key #
`my_dict = {'a': 10, 'b': 20} my_dict['c']` Exception: KeyError 'c' `my_dict.get('c')` None `my_dict.get('c', 'Nothing')` 'Nothing'	`my_obj = {'a': 10, 'b': 20};my_obj['c'];` undefined `my_obj.c;` undefined

Creation of dictionary / object #

my_dict = {'a': 10, 'b': 20}
my_dict['a']

my_dict.a

Exception: AttributeError
'dict' object has no attribute 'a'

var my_obj = {a: 10, b: 20};my_obj['a'];

my_obj.a;

You can access elements of an object either with square brackets or with dot-notation.

var my_obj = {'long key': 'some value', 
               short_key: 'other value'}my_obj['long key'];

some value

my_obj['short_key'];

other value

my_obj.short_key;

other value

Modification of a value in dictionary / object #

my_dict = {'a': 10, 'b': 20}
my_dict['a'] = 'hello'
my_dict['a']

'hello'

var my_obj = {a: 10, b: 20};
my_obj['a'] = 'hello';my_obj['a'];

hello

var my_obj = {a: 10, b: 20};
my_obj.a = 'hello';my_obj['a'];

hello

Two ways of access (square brackets and dot-notation) gives the same element.

Non-string keys #

my_dict = {}
my_dict[5] = 'hello'
my_dict['5'] = 'world'
my_dict

{5: 'hello', '5': 'world'}

var my_obj = {};
my_obj[5] = 'hello';
my_obj['5'] = 'world';my_obj;

{ '5': 'world' }

my_obj[ ['5'] ];

world

Keys of elements in JavaScript object has to be string. Any other key will be coerced to string.

Check if element with given key exists #

my_dict = {'a': 10, 'b': 20}
'a' in my_dict

True

my_obj = {a: 10, b: 20};'a' in my_obj;

true

Access to non-existent key #

my_dict = {'a': 10, 'b': 20}
my_dict['c']

Exception: KeyError
'c'

my_dict.get('c')

None

my_dict.get('c', 'Nothing')

'Nothing'

my_obj = {'a': 10, 'b': 20};my_obj['c'];

undefined

my_obj.c;

undefined

Python.v.JavaScript

JavaScript for Pythonistas. Python for JavaScripters

Dicts / objects

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