what’s the point of object orientation? - europython 2016 · what’s the point of object...
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EuroPython 2016
What’s the point ofObject Orientation?
Iwan Vosloo
EuroPython 2016
Introduction
About
ValidationConstraint
Action
Layout
Button
post.save()
https://goo.gl/3DMHFH
EuroPython 2016
Introduction
About
https://goo.gl/3DMHFH
data_table = DataTable(view, ….. )
EuroPython 2016
Introduction
About / 2
EuroPython 2016
Introduction
OOP is not OO
Supporting mechanisms
for OO
Conceptual modelof a
problem domain
Programminglanguage
map to
Code
EuroPython 2016
Introduction
Cause and effect
EuroPython 2016
Introduction
Understand a program?
EuroPython 2016
Introduction
Scaling up
100 lines
of code?
Courtesy: inkwellideas.com
EuroPython 2016
Introduction
How about...
180 000 lines
of code?
EuroPython 2016
Introduction
Understanding
opportunity
useless
informationdanger
EuroPython 2016
Introduction
A scary thought
EuroPython 2016
ConceptsA conceptual model
Chair
EuroPython 2016
Concepts
Concepts as sets
ChairDesk
EuroPython 2016
Concepts
Refinement via subsetsChair
OfficeChair
EuroPython 2016
Relations
Connecting objectsChair Desk
EuroPython 2016
Relations
Relation as a concept
Assignment
EuroPython 2016
Relations
MultiplicityChair Desk
EuroPython 2016
Notation
It gets complicated...
ChairDesk
AssignmentOfficeChair
EuroPython 2016
Notation
UML
Desk
Chair
OfficeChairassignment 1*
EuroPython 2016
More on concepts
Intangible concepts
PortfolioInvestmentInstrument
UnitTrust
EuroPython 2016
More on concepts
Overlapping concepts
Person
Investor
EuroPython 2016
More on concepts
Changing classification
Person
EmployeeInvestor
EuroPython 2016
More on concepts
Concept labels
Concept
Synonym
Type
Concept
Label
Chair
EuroPython 2016
Affecting objects
Operations
Price PriceFileUnitTrustFund
*
load_prices( )
EuroPython 2016
Summary
Operations vs methods
Operation Object1..*operates on
Method1..*
1
is implemented by
EuroPython 2016
Summary
OO conceptsObject
Type classifies
0..*
subtype0..*
Relation
links
2..*
Operation
1..*
operates on
Method
implemented by1..*
EuroPython 2016
How can this help?
Programs are programs
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Concept
Concept
EuroPython 2016
How can this help?
Understanding-structured
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parse_file:Operation
parse_xml:Method
parse_csv:Method
EuroPython 2016
How can this help?
Focus on one thing
FileFormatPriceFile
EuroPython 2016
How can this help?
Zoom in
FileFormat
Excel CSV
EuroPython 2016
How can this help?
Zoom in more
def parse_file(price_file): for row in price_file: yield row.split(‘,’)
EuroPython 2016
Implementing OO
OOP and Python
ObjectOriented
Programming
ClassicalOOP
PrototypeBased
OOP implementation
EuroPython 2016
Classical OOP & PythonTypes as classes
an instance
an instance
an instance
EuroPython 2016
Classical OOP & PythonPython cookies
>>> class InvestmentInstrument:... pass
>>> fund = InvestmentInstrument()>>> fund<InvestmentInstrument object at 0x7f6815559fd0>
>>> isinstance(fund, InvestmentInstrument)True
>>> type(fund)<class ‘InvestmentInstrument’>
EuroPython 2016
Classical OOP & PythonRelationships as attributes
Portfolio Person
Me
You
owner
owner
EuroPython 2016
Classical OOP & PythonAttributes
>>> portfolio = Portfolio()>>> someone = Person()>>> portfolio.owner = someone
>>> portfolio.owner<Person instance at 0x7fd6d88100e0>
EuroPython 2016
Classical OOP & PythonMethods as (Python)methods
InvestmentInstrument
def activate(self): self.is_active = True
indexed by class
Operation
EuroPython 2016
Classical OOP & PythonA Python method
class InvestmentInstrument:
def activate(self): self.is_active = True
>>> fund = InvestmentInstrument()>>> InvestmentInstrument.activate(fund)
>>> fund.is_activeTrue >>> fund.activate()
EuroPython 2016
Classical OOP & PythonInitialising instances
class InvestmentInstrument: def __init__(self): self.is_active = False
def activate(self): self.is_active = True
>>> fund = InvestmentInstrument()>>> fund.is_activeFalse>>> fund.activate()
EuroPython 2016
Classical OOP & PythonSubtyping 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
EuroPython 2016
Classical OOP & PythonSubtyping as inheritance
>>> fund = UnitTrustFund()>>> isinstance(fund, InvestmentInstrument)True
>>> fund.activate()>>> fund.is_activeTrue
EuroPython 2016
Classical OOP & PythonThe ghost of operations
FileFormat
Excel CSV
parse( )
EuroPython 2016
Classical OOP & PythonThe 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
EuroPython 2016
Classical OOP & PythonThe ghost of operations
FileFormatPriceFile
for line in price_file.format.parse(price_file):# do stuff with line
EuroPython 2016
Classical OOP & PythonThe 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
EuroPython 2016
Design
What’s design?Person
Employee
Investor
Person Role
Employee Investor
Company
EuroPython 2016
Design
Worse designCommissionCalc
Bundles QuoteBasis
QuoteFeesCommissions
AbstractCommissionBundle
*
QuoteBenefit BenefitSummary
Calc
* BenefitGrouping
*
*QuoteBenefit
BundlesBenefit
Calc
*
CommissionBundle
AlteredCommissionBundle
*
LookupCommissionScale
LookupCommissionScaleFactory
*
CalculationConstants
EuroPython 2016
Design
Better designQuoteScenario
Benefit Category*
*
*
*
CommisionBundle
includedInAPI?negotiatedMax (R or %LOA)
CommissionScale
*Product
VAT
BenefitGrouping*
CommissionBand
EuroPython 2016
Design
Inheritance vs subtyping
ObjectTable
ObjectTableWithFilters
ObjectTable Filter0..*
Report ObjectTable
Filter*
ObjectTableByDate
EuroPython 2016
Thanks
On groups.google.com:● reahl-discuss
www.reahl.org
James Martin & James Odell:Object Oriented Methods: A Foundation
Martin Fowler: Refactoring
Slides: https://goo.gl/NPLnCf