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<!doctype html><html><head><meta charset="utf-8"><meta name="description" content="Introducing dry-python"><meta name="author" content="Artem Malyshev"><meta name="apple-mobile-web-app-capable" content="yes"><meta name="apple-mobile-web-app-status-bar-style" content="black-translucent"><meta name="viewport" content="width=device-width,initial-scale=1,maximum-scale=1,user-scalable=no"><title>Introducing dry-python</title><link href="reveal.css" rel="stylesheet"></head><body><div class="reveal"><div class="slides"><section><h2>Introducing</h2><h1><a href="https://dry-python.org/">dry-python</a></h1><h4>Artem Malyshev</h4></section><section><h2>BIO</h2><ul><li>Co-Founder at <a href="https://drylabs.io/">drylabs.io</a></li><li><a href="https://dry-python.org/">dry-python.org</a></li><li>Django Channels 1.0</li><li>5 years of experience in Python</li></ul></section><section><h2>Code is...</h2><p class="fragment"><b>hard</b></p><p class="fragment"><b>and frustrating</b></p><p class="fragment">Let's consider we're developing subscription button for a web service</p></section><section data-background-image="cdb5a8286d2f91cc4960fa5c1a9711c2.jpg" data-background-size="contain"><h2 style="color: white; background-color: black">Startup</h2><br><br><br><br><br><br><br><br></section><section><h2>Micro framework</h2><ol><li class="fragment">Long handlers</li><li class="fragment">Lots of "if" statements</li></ol></section><section><h2>Long handlers</h2><pre><code class="python"> 85 @app.route('/subscriptions/')
 86 def buy_subscription(page):
...
121     if props[-1].endswith('$'):
122 -&gt;      props[-1] = props[-1][:-1]
123</code></pre><pre class="fragment"><code class="python">Traceback (most recent call last):
  File "views.py", line 1027, in buy_subscription
ZeroDivisionError: division by zero</code></pre></section><section data-background-image="3631261faf85567f77566aba22830b8b.jpg" data-background-size="contain"><h2 style="color: white; background-color: black">Enterprise</h2><br><br><br><br><br><br><br><br></section><section><h2>Big framework</h2><ol><li class="fragment">You need method flowchart</li><li class="fragment">Zig-zag in the traceback</li><li class="fragment">Framework internals leak</li></ol></section><section><h2>Implicit API</h2><pre><code class="python">class SubscriptionViewSet(viewsets.ModelViewSet):
    queryset = Subscription.objects.all()
    serializer_class = SubscriptionSerializer
    permission_classes = (CanSubscribe,)
    filter_class = SubscriptionFilter</code></pre><ol><li class="fragment">What exactly does this class do?</li><li class="fragment">How to use it?</li></ol></section><section data-background-image="09172fe1c142acb120d0c205f28f435e.png" data-background-size="contain"><br></section><section><h2>Framework internals leak</h2><pre><code class="python">class SubscriptionSerializer(Serializer):
    category_id = IntegerField()
    price_id = IntegerField()</code></pre><pre class="fragment"><code class="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)</code></pre></section><section><h2>As a result code is...</h2><ol><li class="fragment">Fragile</li><li class="fragment">Hard to reason about</li><li class="fragment">Time-consuming</li></ol></section><section><img src="8414a0e844a1f90c2f79d3c3e89e916b.png"></section><section><blockquote><p>If your code is crap, stickies on the wall won't help.</p><a href="https://twitter.com/henrikkniberg">@HenrikKniberg</a><img src="e4f51d176293502ca62a354118e81189.jpg"></blockquote></section><section><h2>Service layer</h2><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><p><b>by Randy Stafford</b></p></section><section><h2>Business objects</h2><pre><code class="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 &lt; 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)</code></pre></section><section><h2>Business object problems</h2><ol><li class="fragment">Mixed state, implementation and specification</li><li class="fragment">Growth problem</li><li class="fragment">Top-down architecture</li></ol></section><section><img class="plain" src="https://raw.githubusercontent.com/dry-python/brand/master/logo/dry-python.png"><p>A set of libraries for pluggable business logic components.</p><p>Answers how we decompose and organize business logic.</p></section><section><img class="plain" src="https://raw.githubusercontent.com/dry-python/brand/master/logo/stories.png"><p>Define a user story in the business transaction DSL.</p><p>Separate state, implementation and specification.</p></section><section><h2>DSL</h2><pre><code class="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</code></pre></section><section><h2>Context</h2><pre><code class="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 = &lt;User: 3292&gt; # Story argument
  category = &lt;Category: 1318&gt;
    # Set by Subscription.find_category</code></pre></section><section data-background-image="41a288079292c670fc6adbb991c81b5d.png" data-background-size="contain"><h2>DEBUG TOOLBAR</h2><br><br><br><br><br><br><br><br><br><br></section><section data-background-image="2112306ed16594557ec48c5aadcb9840.png" data-background-size="contain"><h2 style="color: white">py.test</h2></section><section data-background-image="ea36d933df7211c5a711818f2145d767.png" data-background-size="contain"><h2>Sentry</h2></section><section><h2>Usage</h2><ol><li class="fragment">Story decorator build an execution plan<pre><code class="python">class Subscription:
    @story
    def buy(I):
        I.find_category</code></pre></li><li class="fragment">Execute object methods according to plan<pre><code class="python">def find_category(self, ctx):
    category = Category.objects.get(
        pk=ctx.category_id)
    return Success(category=category)</code></pre></li><li class="fragment">We call the story method<pre><code class="python">subs = Subscription()
subs.buy(category_id=1, price_id=1)</code></pre></li></ol></section><section><h2>Failures</h2><ol><li class="fragment">Define a number of reasons<pre><code class="python">@Subscription.buy.failures
class Errors(Enum):
    low_balance = auto()</code></pre></li><li class="fragment">Failure will stop the execution of the whole story<pre><code class="python">def check_balance(self, ctx):
    if ctx.profile.balance &lt; ctx.price.cost:
        return Failure(Errors.low_balance)
    else:
        return Success()</code></pre></li><li class="fragment">We check failure reason<pre><code class="python">result = Subscription().buy.run(category_id=2)
assert result.failed_because(Errors.low_balance)</code></pre></li></ol></section><section><h2>Contract</h2><ol><li class="fragment">Define a number of variable validators<pre><code class="python">from pydantic import BaseModel

@Subscription.buy.contract
class Context(BaseModel):
    user: User
    category_id: int
    category: Optional[Category]</code></pre></li><li class="fragment">Return variables from step<pre><code class="python">def find_category(self, ctx: "Context"):
    category = get_category(
        ctx.category_id)
    return Success(category=category)</code></pre></li></ol></section><section><h2>Substories</h2><ol><li class="fragment">Steps can be stories as well<pre><code class="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</code></pre></li><li class="fragment">Each step can stop the execution of current substory<pre><code class="python">def check_code_expiration(self, ctx):
    if ctx.promo_code.is_expired():
        return Skip()
    else:
        return Success()</code></pre></li></ol></section><section><img class="plain" src="https://raw.githubusercontent.com/dry-python/brand/master/logo/dependencies.png"><p>Provide composition instead of inheritance.</p><p>Solves top-down approach problem.</p></section><section><h2>Delegate responsibility</h2><pre><code class="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</code></pre></section><section><h2>Injection</h2><pre><code class="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)</code></pre></section><section><h2>Django views</h2><pre><code class="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('&lt;h1&gt;Not enough money&lt;/h1&gt;')</code></pre></section><section><h2>Flask views</h2><pre><code class="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 '&lt;h1&gt;Not enough money&lt;/h1&gt;'</code></pre></section><section><h2>Celery Tasks</h2><pre><code class="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)</code></pre></section><section><h2>Plans</h2><ol><li>Delegates</li><li>Rollbacks</li><li>asyncio support</li><li>pyramid support</li><li>typing advantages</li><li>linters integration</li><li>language server</li></ol></section><section><h2>Try it!</h2><pre><code>$ pip install stories</code></pre><pre><code>$ pip install dependencies</code></pre></section><section><h2>Get in touch</h2><ul><li><a href="https://dry-python.org/">dry-python.org</a></li><li><a href="https://twitter.com/dry_py">twitter.com/dry_py</a></li><li><a href="https://github.com/dry-python">github.com/dry-python</a></li><li><a href="https://gitter.im/dry-python">gitter.im/dry-python</a></li></ul></section></div></div><script src="reveal.js"></script></body></html>