introducing-dry-python.pug

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    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
        section(data-background-image=require("./pics/startup.jpg").default data-background-size="contain")
          h2(style="color: white; background-color: black") Startup
          br
          br
          br
          br
          br
          br
          br
          br
        section
          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
        section(data-background-image=require("./pics/enterprise.jpg").default data-background-size="contain")
          h2(style="color: white; background-color: black") Enterprise
          br
          br
          br
          br
          br
          br
          br
          br
        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?
        section(data-background-image=require("./pics/method-flowchart.png").default data-background-size="contain")
          br
        section
          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
        section(data-background-image=require("./pics/debug-toolbar.png").default data-background-size="contain")
          h2 DEBUG TOOLBAR
          br
          br
          br
          br
          br
          br
          br
          br
          br
          br
        section(data-background-image=require("./pics/pytest.png").default data-background-size="contain")
          h2(style="color: white") py.test
        section(data-background-image=require("./pics/sentry.png").default data-background-size="contain")
          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