Last Update: 12/12/2019

I wrote this guide to different Ruby idioms and how to do them in Python. Organization is alphabetical. This will have to be a continually updated document as I keep finding holes in my Python knowledge and my prior practice of "Learn it / Blog it" simply doesn't put enough things into the same place. I need a single, easily searchable place to store all this random "how to do X cruft".

This is written as headings which discuss the problem and then how it is done in Ruby and in Python and then, optionally, a Python context. Hopefully this approach makes it useful to both ruby-ites and python-istas.

Note 1: My day to day lingua franca is still Ruby and in a Rails style context where everything is autoloaded. Python to me is a specialized tool for Data Science / Machine Learning. I find that Python:

  • Lacks the elegant simplicity of Ruby
  • Python syntax makes my eyes want to bleed, can we have an underscore character please, how about a colon or some more parentheses
  • Is developer hostile by default

Note 2: These are opinions! I am writing them after a craptastic work day so that and lack of sleep may be tilting my opinions more than a bit; I mean I'm right but still … And please understand that I fundamentally respect that amazing work that Guido did but I find myself in Matz's camp by preference. Still nothing else has the ecosystem that Python does.

Note 3: If you disagree with the above, my twitter handle is fuzzygroup and my email is easily discoverable. Let the fun begin …

Note 4: This was initially written in late 2019 so the Python flavor / version is 3.7 using VirtualEnv on a Mac with pip3.

Note 5: If there's things you want to see here then actually do let me know. This isn't a planned out document, it is more of a "what made me feel stooopid in Python today" type of thing.


The ruby is:


The python is:


Getting All Attributes of an Object

Most Ruby objects, at least in a Rails context, are generally ActiveRecord objects and respond to .attributes so:

plan = Plan.first
2.6.3 :016 > plan.attributes
             "id" => 1,
     "created_at" => Sat, 27 Jul 2019 08:28:17 UTC +00:00,
     "updated_at" => Sat, 27 Jul 2019 08:28:17 UTC +00:00,
           "name" => "Write Daily",
    "public_name" => nil,
    "description" => nil,
        "options" => nil,
        "user_id" => 1,
    "category_id" => nil,
     "has_habits" => nil,
    "habit_count" => 3,
      "shareable" => false,
    "master_plan" => false,
         "active" => true

The python equivalent of this is is to reference the object's internal dict. Below we have an object called message which is coming in from a streaming data solution called sse:

{'data': '{"all_awardings":[],"approved_at_utc":null,"ups":1,"user_reports":[]}', 'event': 'rc', 'id': '33288433929', 'retry': None}

# There are four different top level things that can be called:

# despite the appearance, the attributes of data are NOT json buy just a string so this doesn't work:
*** AttributeError: 'str' object has no attribute 'keys'

Getting All Methods for an Object

The ruby is:

hash = {'foo': 'bar', 'cat': 'blepp'}
(hash.methods - Object.methods).sort

(hash.methods - Object.methods).sort
    [  0] :[],
    [  1] :[]=,
    [  2] :all?,
    [  3] :any?,
    [  4] :assert_valid_keys,
    [  5] :assoc,
    [  6] :chain,
    [  7] :chart_json,
    [  8] :chunk,
    # a crap ton of methods omitted for clarity

# Also and BETTER since it just shows methods on the class; not inherited methods:

    [ 0]                          active_habits()      Plan
    [ 1]                   after_add_for_habits()      Plan
    [ 2]                  after_add_for_habits=(val)   Plan
    [ 3]                  after_add_for_habits?()      Plan
    [ 4]                after_remove_for_habits()      Plan
    [ 5]               after_remove_for_habits=(val)   Plan
    [ 6]               after_remove_for_habits?()      Plan
    [ 7] autosave_associated_records_for_habits(*args) Plan
    [ 8]                  before_add_for_habits()      Plan
    [ 9]                 before_add_for_habits=(val)   Plan
    [10]                 before_add_for_habits?()      Plan
    [11]               before_remove_for_habits()      Plan
    [12]              before_remove_for_habits=(val)   Plan
    [13]              before_remove_for_habits?()      Plan
    [14]                                    foo(bar)   Plan
    [15] validate_associated_records_for_habits(*args) Plan

The python is:

['__class__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__le__', '__lt__', '__module__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '__weakref__', 'data', 'dump', 'event', 'id', 'parse', 'retry', 'sse_line_pattern']
(Pdb) message.sse_line_pattern
re.compile('(?P<name>[^:]*):?( ?(?P<value>.*))?')
# object.__dict__ gets you an object's data while dir(object) gets you an object's methods

See: Me, Lerner, Swlh, Stack Overflow

Getting All Keys in a Hash

The ruby is:

hash = {'foo': 'bar', 'cat': 'blepp'}
2.6.3 :018 > hash.keys
    [0] :foo,
    [1] :cat

The python is:

hash = {'foo': 'bar', 'cat': 'blepp'}
dict_keys(['foo', 'cat'])

JSON Parsing

The ruby is:

json_str = '{"id": 12345, "message": "hello", "array": [1,2,3,4]}'
json = JSON.parse(json_str)
         "id" => 12345,
    "message" => "hello",
      "array" => [
        [0] 1,
        [1] 2,
        [2] 3,
        [3] 4

The python is:

import ujson as JSON

json_str = '{"id": 12345, "message": "hello", "array": [1,2,3,4]}'
json = JSON.loads(json_str)
{'id': 12345, 'message': 'hello', 'array': [1, 2, 3, 4]}
dict_keys(['id', 'message', 'array'])

I will confess to dipping into a bit of a Ruby idiom here by importing ujson as JSON (all caps). I find myself constantly making errors in python by calling my json variable json when that's actually an imported class / module. This one change makes things a lot easier (at least for me).

Length / Size of an Object

The ruby is:

The python is:


Quitting the console

The ruby is:


The python is:



The ruby is:

require 'redis'

2.6.3 :005 > redis =
#<Redis client v4.1.3 for redis://>
2.6.3 :006 > redis.set("mykey", "hello world")
2.6.3 :007 > redis.get("mykey")
"hello world"

The python is:

>>> import redis
>>> r = redis.Redis(host='localhost', port=6379, db=0)
>>> r.set('mykey', 'hello world')
>>> r.get('mykey')
'hello world'

String Interpolation

The ruby is:

skill = "beginner"
puts "Scott is a #{skill}"

The python is:

skill = "beginner"
print(f"Scott is a {skill}")

Try / & - Safe Navigation and Python Hashes

A ruby hash returns nil if the key specified is missing:

2.3.1 :003 > ENV['RUBY_VERSION']

A python dict raises an exception:

import os

>>> os.environ['RAILS_ENV']
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/sjohnson/Sync/fuzzygroup/adl/antihate/antihate_experts/venv/bin/../lib/python3.7/", line 678, in __getitem__
    raise KeyError(key) from None
KeyError: 'RAILS_ENV'
>>> os.environ.get('RAILS_ENV')
>>> os.environ.get('RUBY_VERSION')

The ruby way around this would be to use try or the safe navigation operator:

The Blank for Writing the Next Entry

The ruby is:

The python is: