Whats the point of Object Orientation? Iwan Vosloo EuroPython 2016 - - PowerPoint PPT Presentation

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Whats the point of Object Orientation? Iwan Vosloo EuroPython 2016 - - PowerPoint PPT Presentation

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Whats the point of Object Orientation? Iwan Vosloo EuroPython 2016 Introduction About ValidationConstraint Layout Button Action post.save() https://goo.gl/3DMHFH EuroPython 2016 Introduction About data_table = DataTable(view,

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EuroPython 2016

What’s the point of Object Orientation?

Iwan Vosloo

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EuroPython 2016

Introduction

About

ValidationConstraint Action Layout Button post.save()

https://goo.gl/3DMHFH

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EuroPython 2016

Introduction

About

https://goo.gl/3DMHFH

data_table = DataTable(view, ….. )

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EuroPython 2016

Introduction

About / 2

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EuroPython 2016

Introduction

OOP is not OO

Supporting mechanisms for OO Conceptual model

  • f a

problem domain Programming language map to Code

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EuroPython 2016

Introduction

Cause and effect

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EuroPython 2016

Introduction

Understand a program?

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EuroPython 2016

Introduction

Scaling up

100 lines

  • f code?

Courtesy: inkwellideas.com

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EuroPython 2016

Introduction

How about...

180 000 lines

  • f code?
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EuroPython 2016

Introduction

Understanding

  • pportunity

u s e l e s s i n f

  • r

m a t i

  • n

d a n g e r

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EuroPython 2016

Introduction

A scary thought

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EuroPython 2016

Concepts

A conceptual model

Chair

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EuroPython 2016

Concepts

Concepts as sets

Chair Desk

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EuroPython 2016

Concepts

Refinement via subsets

Chair Office Chair

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EuroPython 2016

Relations

Connecting objects

Chair Desk

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EuroPython 2016

Relations

Relation as a concept

Assignment

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EuroPython 2016

Relations

Multiplicity

Chair Desk

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EuroPython 2016

Notation

It gets complicated...

Chair Desk Assignment Office Chair

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EuroPython 2016

Notation

UML

Desk Chair OfficeChair assignment

1 *

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EuroPython 2016

More on concepts

Intangible concepts

Portfolio Investment Instrument UnitTrust

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EuroPython 2016

More on concepts

Overlapping concepts

Person Investor

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EuroPython 2016

More on concepts

Changing classification

Person Employee Investor

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EuroPython 2016

More on concepts

Concept labels

Concept Synonym Type Concept Label Chair

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EuroPython 2016

Affecting objects

Operations

Price PriceFile UnitTrust Fund

* load_prices( )

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EuroPython 2016

Summary

Operations vs methods

Operation Object 1..*

  • perates on

Method 1..* 1 is implemented by

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EuroPython 2016

Summary

OO concepts

Object Type classifies 0..* subtype 0..* Relation links 2..* Operation 1..*

  • perates on

Method implemented by 1..*

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EuroPython 2016

How can this help?

Programs are programs

Courtesy: inkwellideas.com

Concept Concept

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EuroPython 2016

How can this help?

Understanding-structured

Courtesy: inkwellideas.com

parse_file: Operation parse_xml: Method parse_csv: Method

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EuroPython 2016

How can this help?

Focus on one thing

FileFormat PriceFile

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EuroPython 2016

How can this help?

Zoom in

FileFormat Excel CSV

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EuroPython 2016

How can this help?

Zoom in more

def parse_file(price_file): for row in price_file: yield row.split(‘,’)

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EuroPython 2016

Implementing OO

OOP and Python

Object Oriented Programming Classical OOP Prototype Based

OOP implementation

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EuroPython 2016

Classical OOP & Python

Types as classes

an instance an instance an instance

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EuroPython 2016

Classical OOP & Python

Python cookies

>>> class InvestmentInstrument: ... pass >>> fund = InvestmentInstrument() >>> fund <InvestmentInstrument object at 0x7f6815559fd0> >>> isinstance(fund, InvestmentInstrument) True >>> type(fund) <class ‘InvestmentInstrument’>

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EuroPython 2016

Classical OOP & Python

Relationships as attributes

Portfolio Person Me You

  • wner
  • wner
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EuroPython 2016

Classical OOP & Python

Attributes

>>> portfolio = Portfolio() >>> someone = Person() >>> portfolio.owner = someone >>> portfolio.owner <Person instance at 0x7fd6d88100e0>

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EuroPython 2016

Classical OOP & Python

Methods as (Python)methods

Investment Instrument def activate(self): self.is_active = True indexed by class Operation

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EuroPython 2016

Classical OOP & Python

A Python method

class InvestmentInstrument: def activate(self): self.is_active = True >>> fund = InvestmentInstrument() >>> InvestmentInstrument.activate(fund) >>> fund.is_active True >>> fund.activate()

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EuroPython 2016

Classical OOP & Python

Initialising instances

class InvestmentInstrument: def __init__(self): self.is_active = False def activate(self): self.is_active = True >>> fund = InvestmentInstrument() >>> fund.is_active False >>> fund.activate()

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EuroPython 2016

Classical OOP & Python

Subtyping as inheritance

class InvestmentInstrument: def __init__(self): self.is_active = False def activate(self): self.is_active = True class UnitTrustFund(InvestmentInstrument): def value_of(self, units): return units * self.unit_price

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EuroPython 2016

Classical OOP & Python

Subtyping as inheritance

>>> fund = UnitTrustFund() >>> isinstance(fund, InvestmentInstrument) True >>> fund.activate() >>> fund.is_active True

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EuroPython 2016

Classical OOP & Python

The ghost of operations

FileFormat Excel CSV

parse( )

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EuroPython 2016

Classical OOP & Python

The ghost of operations

class CSVFileFormat(FileFormat): def parse(self, price_file): for row in price_file: yield row.split(‘,’) class ExcelFileFormat(FileFormat): def parse(self, price_file): # totally different stuff

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EuroPython 2016

Classical OOP & Python

The ghost of operations

FileFormat PriceFile for line in price_file.format.parse(price_file): # do stuff with line

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EuroPython 2016

Classical OOP & Python

The ghost of operations

if price_file.format.is_csv: lines = parse_csv(price_file) elif price_file.format.is_excel: lines = parse_excel(price_file)

else:

raise Exception(‘not supposed to get here’) for line in lines: # do stuff with line

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EuroPython 2016

Design

What’s design?

Person Employee Investor Person Role Employee Investor Company

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EuroPython 2016

Design

Worse design

CommissionCalc Bundles QuoteBasis QuoteFees Commissions AbstractCommission Bundle * QuoteBenefit Benefit Summary Calc * Benefit Grouping * * QuoteBenefit Bundles Benefit Calc * Commission Bundle Altered CommissionBundle * Lookup CommissionScale LookupCommission ScaleFactory * Calculation Constants

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EuroPython 2016

Design

Better design

QuoteScenario Benefit Category * * * * CommisionBundle

includedInAPI? negotiatedMax (R or %LOA)

Commission Scale * Product

VAT

BenefitGrouping * Commission Band

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EuroPython 2016

Design

Inheritance vs subtyping

ObjectTable ObjectTable WithFilters ObjectTable Filter

0..*

Report ObjectTable Filter

*

ObjectTable ByDate

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EuroPython 2016

Thanks

On groups.google.com:

  • reahl-discuss

www.reahl.org

iwan@reahl.org James Martin & James Odell: Object Oriented Methods: A Foundation Martin Fowler: Refactoring Slides: https://goo.gl/NPLnCf