Clean Architecture Applications in Python

Clean Architecture Applications in Python

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  Clean Architecture Building CleanApps in Python Subhash Bhushan Team8 Solutions, LLC 1
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  Technical Debt Dependencies slowyou down 2 . 2
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  Clean Architecture Reduce TechnicalDebt by Reducing Dependencies Thou shalt only look inward! 3 . 2
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  Example 1. Check Balancein Account 1 2. Initiate Transaction 3. Debit Account 1 4. Credit Account 2 5. Record Transfer 6. Commit Transaction An Implementation of Account to Account Transfer 4 . 1
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  Entities from datetime importdatetime class Account: # Look Ma, No DB! def __init__(self, name, balance): self.name = name self.balance = balance def validate(self): pass def has_sufficient_balance(self, amount): return self.balance >= amount def debit(self, amount): if self.has_sufficient_balance(amount): self.balance -= amount def credit(self, amount): self.balance += amount class Transfer: def __init__(self, from_account: Account, to_account: Account, amount: float): self.from_account = from_account self.to_account = to_account self.amount = amount self.transaction_date = datetime.now() 4 . 2
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  UseCase from core.entities importTransfer from db.repository import TransferRepository class TransferUseCase: def __init__(self, repository: TransferRepository): # Dependency... Injected. self.repository = repository def create(self, transfer: Transfer): if transfer.from_account.validate() and transfer.to_account.validate() and transfer.from_account.has_sufficient_balance(transfer.amount) and self._validate_transfer_request(transfer): with self.repository.atomic(): transfer = self.repository.save(transfer) return transfer def _validate_transfer_request(self, transfer: Transfer): pass 4 . 3
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  Data Adapters from typingimport NamedTuple # Don't Type Hints make your code look great? from core.entities import Transfer from core.usecase import TransferUseCase from db.repository import TransferRepository class AccountData(NamedTuple): name: str balance: float class TransferData(NamedTuple): from_account: AccountData to_account: AccountData amount: float transaction_date: str 4 . 4
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  Interface Adapters from typingimport NamedTuple from core.entities import Transfer from core.usecase import TransferUseCase from db.repository import TransferRepository class TransferAdapter: def __init__(self, repository: TransferRepository): # Some more... Injection. self.usecase = TransferUseCase(repository) def create(self, transfer_data: TransferData) -> TransferData: transfer = self._data_to_transfer(transfer_data) transfer = self.usecase.create(transfer) # Warning: No Exceptions Please! return self._transfer_to_data(transfer) @classmethod def _transfer_to_data(cls, transfer: Transfer) -> TransferData: pass @classmethod def _data_to_transfer(cls, transfer_data: TransferData) -> Transfer: pass 4 . 5
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  Repository from typing importContextManager from core.entities import Transfer class TransferRepository: def save(self, transfer: Transfer) -> Transfer: # And Finally... # Persist Transfer AND Accounts raise NotImplementedError() def atomic(self) -> ContextManager: raise NotImplementedError() 4 . 6
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  Views import json from flaskimport request from flask_restful import Resource, Api from core.adapters import TransferAdapter from db.repository import TransferRepository class TransferResource(Resource): def __init__(self, *args, **kwargs): self.super().__init__(*args, **kwargs) self.adapter = TransferAdapter(TransferRepository()) # Inject... Dependency @app.route('/api/v1.0/transfer', methods=['POST']) def post(self): transfer_data = self.adapter.create(request.form['data']) return transfer_data, 201 # Again, No Exceptions, Please! 4 . 7
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  Cons Everyone needs torespect rules Difficult to leverage frameworks Cannot take advantage of Active Record pattern Can result in Significant Boilerplate Higher Complexity There ain't no such thing as a Free Lunch 5
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  The Principle of LastResponsible Moment A good architecture allows you to defer critical decisions 6 . 1
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  Resources The Clean Architecture- Robert C. Martin's Clean Architecture - Alistair Cockburn - Clean Architecture Python Apps - Clean Architecture is Screaming - Github Repo - 8thlight.com Amazon.com Hexagonal Architecture @haxoza DZone Clean Transfer All Icons are courtesy of the good folks at The Noun Project 6 . 2
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  Thank you! Questions? subhash@team8solutions.com 6 .3