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meta(charset="utf-8")

meta(name="description" content="Introducing dry-python")

meta(name="author" content="Artem Malyshev")

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title Introducing dry-python

body

.reveal

.slides

section

h2 Introducing

h1

a(href="https://dry-python.org/").

dry-python

h4 Artem Malyshev

section

h2 BIO

ul

li Co-Founder at #[a(href="https://drylabs.io/") drylabs.io]

li #[a(href="https://dry-python.org/") dry-python.org]

li Django Channels 1.0

li 5 years of experience in Python

section

h2 Code is...

p.fragment

b hard

p.fragment

b and frustrating

p.fragment Let's consider we're developing subscription button for a web service

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h2(style="color: white; background-color: black") Startup

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h2 Micro framework

ol

li.fragment Long handlers

li.fragment Lots of "if" statements

section

h2 Long handlers

pre

code.python.

85 @app.route('/subscriptions/')

86 def buy_subscription(page):

...

121 if props[-1].endswith('$'):

122 -#{">"} props[-1] = props[-1][:-1]

123

pre.fragment

code.python.

Traceback (most recent call last):

File "views.py", line 1027, in buy_subscription

ZeroDivisionError: division by zero

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h2(style="color: white; background-color: black") Enterprise

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section

h2 Big framework

ol

li.fragment You need method flowchart

li.fragment Zig-zag in the traceback

li.fragment Framework internals leak

section

h2 Implicit API

pre

code.python.

class SubscriptionViewSet(viewsets.ModelViewSet):

queryset = Subscription.objects.all()

serializer_class = SubscriptionSerializer

permission_classes = (CanSubscribe,)

filter_class = SubscriptionFilter

ol

li.fragment What exactly does this class do?

li.fragment How to use it?

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h2 Framework internals leak

pre

code.python.

class SubscriptionSerializer(Serializer):

category_id = IntegerField()

price_id = IntegerField()

pre.fragment

code.python.

def recreate_nested_writable_fields(self, instance):

for field, values in self.writable_fields_to_recreate():

related_manager = getattr(instance, field)

related_manager.all().delete()

for data in values:

obj = related_manager.model.objects.create(

to=instance, **data)

related_manager.add(obj)

section

h2 As a result code is...

ol

li.fragment Fragile

li.fragment Hard to reason about

li.fragment Time-consuming

section

img(src=require("./pics/crazy-telephone-wires.png").default)

section

blockquote

p If your code is crap, stickies on the wall won't help.

a(href="https://twitter.com/henrikkniberg").

@HenrikKniberg

img(src=require("./pics/stickers-on-the-wall.jpg").default)

section

h2 Service layer

p Defines an application's boundary with a layer of services that establishes a set of available operations and coordinates the application's response in each operation.

p

b by Randy Stafford

section

h2 Business objects

pre

code.python.

def buy_subscription(category_id, price_id, user):

category = find_category(category_id)

price = find_price(price_id)

profile = find_profile(user)

if profile.balance #{"<"} price.cost:

raise ValueError

decrease_balance(profile, price.cost)

save_profile(profile)

expires = calculate_period(price.period)

subscription = create_subscription(

profile, category, expires)

notification = send_notification(

'subscription', profile, category.name)

section

h2 Business object problems

ol

li.fragment Mixed state, implementation and specification

li.fragment Growth problem

li.fragment Top-down architecture

section

img(src="https://raw.githubusercontent.com/dry-python/brand/master/logo/dry-python.png").plain

p A set of libraries for pluggable business logic components.

p Answers how we decompose and organize business logic.

section

img(src="https://raw.githubusercontent.com/dry-python/brand/master/logo/stories.png").plain

p Define a user story in the business transaction DSL.

p Separate state, implementation and specification.

section

h2 DSL

pre

code.python.

from stories import story, arguments

class Subscription:

@story

@arguments('category_id', 'price_id')

def buy(I):

I.find_category

I.find_price

I.find_profile

I.check_balance

I.persist_payment

I.persist_subscription

I.send_subscription_notification

section

h2 Context

pre

code.python.

(Pdb) ctx

Subscription.buy:

find_category

check_price

check_purchase (PromoCode.validate)

find_code (skipped)

check_balance

find_profile

Context:

category_id = 1318 # Story argument

user = #{"<"}User: 3292#{">"} # Story argument

category = #{"<"}Category: 1318#{">"}

# Set by Subscription.find_category

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h2 DEBUG TOOLBAR

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h2(style="color: white") py.test

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h2 Sentry

section

h2 Usage

ol

li.fragment Story decorator build an execution plan

pre

code.python.

class Subscription:

@story

def buy(I):

I.find_category

li.fragment Execute object methods according to plan

pre

code.python.

def find_category(self, ctx):

category = Category.objects.get(

pk=ctx.category_id)

return Success(category=category)

li.fragment We call the story method

pre

code.python.

subs = Subscription()

subs.buy(category_id=1, price_id=1)

section

h2 Failures

ol

li.fragment Define a number of reasons

pre

code.python.

@Subscription.buy.failures

class Errors(Enum):

low_balance = auto()

li.fragment Failure will stop the execution of the whole story

pre

code.python.

def check_balance(self, ctx):

if ctx.profile.balance #{"<"} ctx.price.cost:

return Failure(Errors.low_balance)

else:

return Success()

li.fragment We check failure reason

pre

code.python.

result = Subscription().buy.run(category_id=2)

assert result.failed_because(Errors.low_balance)

section

h2 Contract

ol

li.fragment Define a number of variable validators

pre

code.python.

from pydantic import BaseModel

@Subscription.buy.contract

class Context(BaseModel):

user: User

category_id: int

category: Optional[Category]

li.fragment Return variables from step

pre

code.python.

def find_category(self, ctx: "Context"):

category = get_category(

ctx.category_id)

return Success(category=category)

section

h2 Substories

ol

li.fragment Steps can be stories as well

pre

code.python.

class Subscription:

@story

def buy(I):

I.calculate_discount

I.check_balance

@story

def calculate_discount(I):

I.find_promo_code

I.check_code_expiration

li.fragment Each step can stop the execution of current substory

pre

code.python.

def check_code_expiration(self, ctx):

if ctx.promo_code.is_expired():

return Skip()

else:

return Success()

section

img(src="https://raw.githubusercontent.com/dry-python/brand/master/logo/dependencies.png").plain

p Provide composition instead of inheritance.

p Solves top-down approach problem.

section

h2 Delegate responsibility

pre

code.python.

class Subscription:

def find_category(self, ctx):

category = self.load_category(ctx.category_id)

return Success(category=category)

def find_price(self, ctx):

price = self.load_price(ctx.price_id)

return Success(price=price)

def __init__(self, load_category, load_price):

self.load_category = load_category

self.load_price = load_price

section

h2 Injection

pre

code.python.

from dependencies import Injector, Package

app = Package('app')

class BuySubscription(Injector):

buy_subscription = app.services.Subscription.buy

load_category = app.repositories.load_category

load_price = app.repositories.load_price

load_profile = app.repositories.load_profile

BuySubscription.buy_subscription(category_id=1, price_id=1)

section

h2 Django views

pre

code.python.

from dependencies import operation

from dependencies.contrib.django import view

from django.http import HttpResponse, HttpResponseRedirect

@view

class BuySubscriptionView(BuySubscription):

@operation

def post(buy_subscription, category_id, price_id):

result = buy_subscription.run(category_id, price_id)

if result.is_success:

return HttpResponseRedirect(to=result.value)

elif result.failed_on('check_balance'):

return HttpResponse('#{"<"}h1#{">"}Not enough money#{"<"}/h1#{">"}')

section

h2 Flask views

pre

code.python.

from dependencies import operation

from dependencies.contrib.flask import method_view

from flask import redirect

@method_view

class BuySubscriptionView(BuySubscription):

@operation

def post(buy_subscription, category_id, price_id):

result = buy_subscription.run(category_id, price_id)

if result.is_success:

return redirect(result.value)

elif result.failed_on('check_balance'):

return '#{"<"}h1#{">"}Not enough money#{"<"}/h1#{">"}'

section

h2 Celery Tasks

pre

code.python.

from dependencies import operation

from dependencies.contrib.celery import task

@task

class PutMoneyTask(PutMoney):

@operation

def run(put_money, user, amount, task):

result = put_money.run(user, amount)

if result.is_failure:

task.on_failure(result.ctx.transaction_id)

section

h2 Plans

ol

li Delegates

li Rollbacks

li asyncio support

li pyramid support

li typing advantages

li linters integration

li language server

section

h2 Try it!

pre

code.

$ pip install stories

pre

code.

$ pip install dependencies

section

h2 Get in touch

ul

li

a(href="https://dry-python.org/") dry-python.org

li

a(href="https://twitter.com/dry_py") twitter.com/dry_py

li

a(href="https://github.com/dry-python") github.com/dry-python

li

a(href="https://gitter.im/dry-python") gitter.im/dry-python