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Announcements
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61A Lecture 18 Friday, March 6 Announcements 2 Announcements - - PowerPoint PPT Presentation
61A Lecture 18 Friday, March 6 Announcements 2 Announcements - - PowerPoint PPT Presentation
61A Lecture 18 Friday, March 6 Announcements 2 Announcements Project 3 due Thursday 3/12 @ 11:59pm (get started now!) 2 Announcements Project 3 due Thursday 3/12 @ 11:59pm (get started now!) Project party on Tuesday 3/10
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SLIDE 3
Announcements
- Project 3 due Thursday 3/12 @ 11:59pm (get started now!)
2
SLIDE 4
Announcements
- Project 3 due Thursday 3/12 @ 11:59pm (get started now!)
§Project party on Tuesday 3/10 5pm-6:30pm in 2050 VLSB
2
SLIDE 5
Announcements
- Project 3 due Thursday 3/12 @ 11:59pm (get started now!)
§Project party on Tuesday 3/10 5pm-6:30pm in 2050 VLSB §Bonus point for early submission by Wednesday 3/11
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SLIDE 6
Announcements
- Project 3 due Thursday 3/12 @ 11:59pm (get started now!)
§Project party on Tuesday 3/10 5pm-6:30pm in 2050 VLSB §Bonus point for early submission by Wednesday 3/11
- Homework 6 due Monday 3/16 @ 11:59pm (not yet released)
2
SLIDE 7
Announcements
- Project 3 due Thursday 3/12 @ 11:59pm (get started now!)
§Project party on Tuesday 3/10 5pm-6:30pm in 2050 VLSB §Bonus point for early submission by Wednesday 3/11
- Homework 6 due Monday 3/16 @ 11:59pm (not yet released)
- Midterm 2 is on Thursday 3/19 7pm-9pm
2
SLIDE 8
Announcements
- Project 3 due Thursday 3/12 @ 11:59pm (get started now!)
§Project party on Tuesday 3/10 5pm-6:30pm in 2050 VLSB §Bonus point for early submission by Wednesday 3/11
- Homework 6 due Monday 3/16 @ 11:59pm (not yet released)
- Midterm 2 is on Thursday 3/19 7pm-9pm
§Emphasis: mutable data, object-oriented programming, recursion, and recursive data
2
SLIDE 9
Announcements
- Project 3 due Thursday 3/12 @ 11:59pm (get started now!)
§Project party on Tuesday 3/10 5pm-6:30pm in 2050 VLSB §Bonus point for early submission by Wednesday 3/11
- Homework 6 due Monday 3/16 @ 11:59pm (not yet released)
- Midterm 2 is on Thursday 3/19 7pm-9pm
§Emphasis: mutable data, object-oriented programming, recursion, and recursive data §Fill out conflict form if you cannot attend due to a course conflict
2
SLIDE 10
Hog Contest Results
3
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Hog Contest Results
Excellent participation! 51 qualified submissions Lots of excellent ideas
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SLIDE 12
Hog Contest Results
Excellent participation! 51 qualified submissions Lots of excellent ideas
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SLIDE 13
Hog Contest Results
Excellent participation! 51 qualified submissions Lots of excellent ideas
3
(Results)
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Type Coercion
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Review: Type Dispatching Analysis
5
Minimal violation of abstraction barriers: we define cross-type functions as necessary. Extensible: Any new numeric type can "install" itself into the existing system by adding new entries to the cross-type function dictionaries
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Review: Type Dispatching Analysis
Arg 1 Arg 2 Add Multiply Complex Complex Rational Rational Complex Rational Rational Complex
5
Minimal violation of abstraction barriers: we define cross-type functions as necessary. Extensible: Any new numeric type can "install" itself into the existing system by adding new entries to the cross-type function dictionaries
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Coercion
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SLIDE 18
Coercion
Idea: Some types can be converted into other types
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SLIDE 19
Coercion
Idea: Some types can be converted into other types Takes advantage of structure in the type system
6
SLIDE 20
Coercion
Idea: Some types can be converted into other types Takes advantage of structure in the type system def rational_to_complex(r): """Return complex equal to rational.""" return ComplexRI(r.numer/r.denom, 0)
6
SLIDE 21
Coercion
Idea: Some types can be converted into other types Takes advantage of structure in the type system def rational_to_complex(r): """Return complex equal to rational.""" return ComplexRI(r.numer/r.denom, 0) Question: Can any numeric type be coerced into any other?
6
SLIDE 22
Coercion
Idea: Some types can be converted into other types Takes advantage of structure in the type system def rational_to_complex(r): """Return complex equal to rational.""" return ComplexRI(r.numer/r.denom, 0) Question: Can any numeric type be coerced into any other?
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Question: Can any two numeric types be coerced into a common type?
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Coercion
Idea: Some types can be converted into other types Takes advantage of structure in the type system def rational_to_complex(r): """Return complex equal to rational.""" return ComplexRI(r.numer/r.denom, 0) Question: Can any numeric type be coerced into any other?
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Question: Can any two numeric types be coerced into a common type? Question: Is coercion exact?
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Applying Operators with Coercion
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SLIDE 25
Applying Operators with Coercion
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class Number:
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Applying Operators with Coercion
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class Number: def __add__(self, other): x, y = self.coerce(other) return x.add(y)
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Applying Operators with Coercion
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class Number: def __add__(self, other): x, y = self.coerce(other) return x.add(y) Always defer to add method
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Applying Operators with Coercion
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class Number: def __add__(self, other): x, y = self.coerce(other) return x.add(y) def coerce(self, other): Always defer to add method
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Applying Operators with Coercion
7
class Number: def __add__(self, other): x, y = self.coerce(other) return x.add(y) def coerce(self, other): if self.type_tag == other.type_tag: return self, other Always defer to add method
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Applying Operators with Coercion
7
class Number: def __add__(self, other): x, y = self.coerce(other) return x.add(y) def coerce(self, other): if self.type_tag == other.type_tag: return self, other Always defer to add method Same interface: no change required
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Applying Operators with Coercion
7
class Number: def __add__(self, other): x, y = self.coerce(other) return x.add(y) def coerce(self, other): if self.type_tag == other.type_tag: return self, other elif (self.type_tag, other.type_tag) in self.coercions: Always defer to add method Same interface: no change required
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Applying Operators with Coercion
7
class Number: def __add__(self, other): x, y = self.coerce(other) return x.add(y) def coerce(self, other): if self.type_tag == other.type_tag: return self, other elif (self.type_tag, other.type_tag) in self.coercions: coercions = {('rat', 'com'): rational_to_complex} Always defer to add method Same interface: no change required
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Applying Operators with Coercion
7
class Number: def __add__(self, other): x, y = self.coerce(other) return x.add(y) def coerce(self, other): if self.type_tag == other.type_tag: return self, other elif (self.type_tag, other.type_tag) in self.coercions: return (self.coerce_to(other.type_tag), other) coercions = {('rat', 'com'): rational_to_complex} Always defer to add method Same interface: no change required
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Applying Operators with Coercion
7
class Number: def __add__(self, other): x, y = self.coerce(other) return x.add(y) def coerce(self, other): if self.type_tag == other.type_tag: return self, other elif (self.type_tag, other.type_tag) in self.coercions: return (self.coerce_to(other.type_tag), other) coercions = {('rat', 'com'): rational_to_complex} Always defer to add method Same interface: no change required def coerce_to(self, other_tag): coercion_fn = self.coercions[(self.type_tag, other_tag)] return coercion_fn(self)
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Applying Operators with Coercion
7
class Number: def __add__(self, other): x, y = self.coerce(other) return x.add(y) def coerce(self, other): if self.type_tag == other.type_tag: return self, other elif (self.type_tag, other.type_tag) in self.coercions: return (self.coerce_to(other.type_tag), other) elif (other.type_tag, self.type_tag) in self.coercions: return (self, other.coerce_to(self.type_tag)) coercions = {('rat', 'com'): rational_to_complex} Always defer to add method Same interface: no change required def coerce_to(self, other_tag): coercion_fn = self.coercions[(self.type_tag, other_tag)] return coercion_fn(self)
SLIDE 36
Applying Operators with Coercion
(Demo)
7
class Number: def __add__(self, other): x, y = self.coerce(other) return x.add(y) def coerce(self, other): if self.type_tag == other.type_tag: return self, other elif (self.type_tag, other.type_tag) in self.coercions: return (self.coerce_to(other.type_tag), other) elif (other.type_tag, self.type_tag) in self.coercions: return (self, other.coerce_to(self.type_tag)) coercions = {('rat', 'com'): rational_to_complex} Always defer to add method Same interface: no change required def coerce_to(self, other_tag): coercion_fn = self.coercions[(self.type_tag, other_tag)] return coercion_fn(self)
SLIDE 37
Coercion Analysis
8
SLIDE 38
Coercion Analysis
Minimal violation of abstraction barriers: we define cross-type coercion as necessary
8
SLIDE 39
Coercion Analysis
Minimal violation of abstraction barriers: we define cross-type coercion as necessary Requires that all types can be coerced into a common type
8
SLIDE 40
Coercion Analysis
Minimal violation of abstraction barriers: we define cross-type coercion as necessary Requires that all types can be coerced into a common type More sharing: All operators use the same coercion scheme
8
SLIDE 41
Coercion Analysis
Minimal violation of abstraction barriers: we define cross-type coercion as necessary Requires that all types can be coerced into a common type More sharing: All operators use the same coercion scheme Arg 1 Arg 2 Add Multiply Complex Complex Rational Rational Complex Rational Rational Complex
8
SLIDE 42
Coercion Analysis
Minimal violation of abstraction barriers: we define cross-type coercion as necessary Requires that all types can be coerced into a common type More sharing: All operators use the same coercion scheme Arg 1 Arg 2 Add Multiply Complex Complex Rational Rational Complex Rational Rational Complex From To Coerce Complex Rational Rational Complex
8
SLIDE 43
Coercion Analysis
Minimal violation of abstraction barriers: we define cross-type coercion as necessary Requires that all types can be coerced into a common type More sharing: All operators use the same coercion scheme Arg 1 Arg 2 Add Multiply Complex Complex Rational Rational Complex Rational Rational Complex From To Coerce Complex Rational Rational Complex Type Add Multiply Complex Rational
8
SLIDE 44
Linked Lists
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Linked List Structure
A linked list is either empty or a first value and the rest of the linked list
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Linked List Structure
A linked list is either empty or a first value and the rest of the linked list
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3 , 4 , 5
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Linked List Structure
A linked list is either empty or a first value and the rest of the linked list
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3 , 4 , 5 first: 3 rest: Link instance
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Linked List Structure
A linked list is either empty or a first value and the rest of the linked list
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3 , 4 , 5 first: 3 rest: Link instance first: 4 rest: Link instance
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Linked List Structure
A linked list is either empty or a first value and the rest of the linked list
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3 , 4 , 5 first: 3 rest: Link instance first: 4 rest: Link instance first: 5 rest: Link instance
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Linked List Structure
A linked list is either empty or a first value and the rest of the linked list
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3 , 4 , 5 Link.empty first: 3 rest: Link instance first: 4 rest: Link instance first: 5 rest: Link instance
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Linked List Structure
A linked list is either empty or a first value and the rest of the linked list
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3 , 4 , 5 Link.empty first: 3 rest: Link instance first: 4 rest: Link instance first: 5 rest: Link instance A linked list is a pair
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Linked List Structure
A linked list is either empty or a first value and the rest of the linked list
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3 , 4 , 5 Link.empty first: 3 rest: Link instance first: 4 rest: Link instance first: 5 rest: Link instance A linked list is a pair The first (zeroth) element is an attribute value
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Linked List Structure
A linked list is either empty or a first value and the rest of the linked list
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3 , 4 , 5 Link.empty first: 3 rest: Link instance first: 4 rest: Link instance first: 5 rest: Link instance A linked list is a pair The first (zeroth) element is an attribute value The rest of the elements are stored in a linked list
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Linked List Structure
A linked list is either empty or a first value and the rest of the linked list
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3 , 4 , 5 Link.empty first: 3 rest: Link instance first: 4 rest: Link instance first: 5 rest: Link instance A linked list is a pair The first (zeroth) element is an attribute value The rest of the elements are stored in a linked list A class attribute represents an empty linked list
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Linked List Structure
A linked list is either empty or a first value and the rest of the linked list
10
3 , 4 , 5 Link.empty first: 3 rest: Link instance first: 4 rest: Link instance first: 5 rest: Link instance Link(3, Link(4, Link(5, Link.empty))) A linked list is a pair The first (zeroth) element is an attribute value The rest of the elements are stored in a linked list A class attribute represents an empty linked list
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Linked List Structure
A linked list is either empty or a first value and the rest of the linked list
11
3 , 4 , 5 first: 3 rest: Link instance first: 4 rest: Link instance first: 5 rest: Link instance Link.empty , Link.empty ) Link(3, Link(4, Link(5 )))
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Linked List Structure
A linked list is either empty or a first value and the rest of the linked list
11
3 , 4 , 5 first: 3 rest: Link instance first: 4 rest: Link instance first: 5 rest: Link instance Link.empty , Link.empty ) Link(3, Link(4, Link(5 )))
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Linked List Structure
A linked list is either empty or a first value and the rest of the linked list
11
3 , 4 , 5 first: 3 rest: Link instance first: 4 rest: Link instance first: 5 rest: Link instance Link.empty , Link.empty ) Link(3, Link(4, Link(5 )))
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Linked List Structure
A linked list is either empty or a first value and the rest of the linked list
11
3 , 4 , 5 first: 3 rest: Link instance first: 4 rest: Link instance first: 5 rest: Link instance Link.empty , Link.empty ) Link(3, Link(4, Link(5 )))
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Linked List Structure
A linked list is either empty or a first value and the rest of the linked list
11
3 , 4 , 5 first: 3 rest: Link instance first: 4 rest: Link instance first: 5 rest: Link instance , Link.empty ) Link(3, Link(4, Link(5 )))
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Linked List Structure
A linked list is either empty or a first value and the rest of the linked list
11
3 , 4 , 5 first: 3 rest: Link instance first: 4 rest: Link instance first: 5 rest: Link instance Link(3, Link(4, Link(5 )))
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Linked List Class
12
Link(3, Link(4, Link(5 )))
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Linked List Class
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Linked list class: attributes are passed to __init__ Link(3, Link(4, Link(5 )))
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Linked List Class
class Link:
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Linked list class: attributes are passed to __init__ Link(3, Link(4, Link(5 )))
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Linked List Class
class Link:
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Linked list class: attributes are passed to __init__ def __init__(self, first, rest=empty): Link(3, Link(4, Link(5 )))
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Linked List Class
class Link:
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Linked list class: attributes are passed to __init__ def __init__(self, first, rest=empty): assert rest is Link.empty or isinstance(rest, Link) Link(3, Link(4, Link(5 )))
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Linked List Class
class Link:
12
Linked list class: attributes are passed to __init__ def __init__(self, first, rest=empty): assert rest is Link.empty or isinstance(rest, Link) self.first = first self.rest = rest Link(3, Link(4, Link(5 )))
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Linked List Class
class Link:
12
Linked list class: attributes are passed to __init__ def __init__(self, first, rest=empty): assert rest is Link.empty or isinstance(rest, Link) self.first = first self.rest = rest Link(3, Link(4, Link(5 ))) Returns whether rest is a Link
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Linked List Class
class Link:
12
Linked list class: attributes are passed to __init__ def __init__(self, first, rest=empty): assert rest is Link.empty or isinstance(rest, Link) self.first = first self.rest = rest Link(3, Link(4, Link(5 ))) Returns whether rest is a Link help(isinstance): Return whether an object is an instance of a class or of a subclass thereof.
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Linked List Class
class Link: empty = ()
12
Linked list class: attributes are passed to __init__ def __init__(self, first, rest=empty): assert rest is Link.empty or isinstance(rest, Link) self.first = first self.rest = rest Link(3, Link(4, Link(5 ))) Returns whether rest is a Link help(isinstance): Return whether an object is an instance of a class or of a subclass thereof.
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Linked List Class
class Link: empty = ()
12
Some zero-length sequence Linked list class: attributes are passed to __init__ def __init__(self, first, rest=empty): assert rest is Link.empty or isinstance(rest, Link) self.first = first self.rest = rest Link(3, Link(4, Link(5 ))) Returns whether rest is a Link help(isinstance): Return whether an object is an instance of a class or of a subclass thereof.
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Linked List Class
class Link: empty = ()
12
Some zero-length sequence Linked list class: attributes are passed to __init__ def __init__(self, first, rest=empty): assert rest is Link.empty or isinstance(rest, Link) self.first = first self.rest = rest (Demo) Link(3, Link(4, Link(5 ))) Returns whether rest is a Link help(isinstance): Return whether an object is an instance of a class or of a subclass thereof.
SLIDE 73
Sequence Operations
SLIDE 74
Linked List Class
14
More special method names: __len__ __getitem__ Element selection [] Built-in len function
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Linked List Class
14
More special method names: __len__ __getitem__ Element selection [] Built-in len function Linked lists are sequences
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Linked List Class
class Link: empty = ()
14
More special method names: __len__ __getitem__ Element selection [] Built-in len function Linked lists are sequences def __init__(self, first, rest=empty): assert ... self.first = first self.rest = rest
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Linked List Class
class Link: empty = ()
14
More special method names: __len__ __getitem__ Element selection [] Built-in len function Linked lists are sequences def __init__(self, first, rest=empty): assert ... self.first = first self.rest = rest def __getitem__(self, i): if i == 0: return self.first else: return self.rest[i-1]
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Linked List Class
class Link: empty = ()
14
This element selection syntax More special method names: __len__ __getitem__ Element selection [] Built-in len function Linked lists are sequences def __init__(self, first, rest=empty): assert ... self.first = first self.rest = rest def __getitem__(self, i): if i == 0: return self.first else: return self.rest[i-1]
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Linked List Class
class Link: empty = ()
14
This element selection syntax Calls this method More special method names: __len__ __getitem__ Element selection [] Built-in len function Linked lists are sequences def __init__(self, first, rest=empty): assert ... self.first = first self.rest = rest def __getitem__(self, i): if i == 0: return self.first else: return self.rest[i-1]
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Linked List Class
class Link: empty = ()
14
This element selection syntax Calls this method More special method names: __len__ __getitem__ Element selection [] Built-in len function Linked lists are sequences def __init__(self, first, rest=empty): assert ... self.first = first self.rest = rest def __getitem__(self, i): if i == 0: return self.first else: return self.rest[i-1] def __len__(self): return 1 + len(self.rest)
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Linked List Class
class Link: empty = () Recursive call to __len__
14
This element selection syntax Calls this method More special method names: __len__ __getitem__ Element selection [] Built-in len function Linked lists are sequences def __init__(self, first, rest=empty): assert ... self.first = first self.rest = rest def __getitem__(self, i): if i == 0: return self.first else: return self.rest[i-1] def __len__(self): return 1 + len(self.rest)
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Linked List Class
class Link: empty = () Recursive call to __len__
14
(Demo) Methods can be recursive too! This element selection syntax Calls this method More special method names: __len__ __getitem__ Element selection [] Built-in len function Linked lists are sequences def __init__(self, first, rest=empty): assert ... self.first = first self.rest = rest def __getitem__(self, i): if i == 0: return self.first else: return self.rest[i-1] def __len__(self): return 1 + len(self.rest)
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