SLIDE 1
61A Lecture 12
Announcements
61A Lecture 12 Announcements Objects (Demo) Objects 4 Objects - - PowerPoint PPT Presentation
61A Lecture 12 Announcements Objects (Demo) Objects 4 Objects - - PowerPoint PPT Presentation
61A Lecture 12 Announcements Objects (Demo) Objects 4 Objects Objects represent information 4 Objects Objects represent information They consist of data and behavior, bundled together to create abstractions 4 Objects
SLIDE 2
SLIDE 3
Objects
(Demo)
SLIDE 4
Objects
4
SLIDE 5
Objects
- Objects represent information
4
SLIDE 6
Objects
- Objects represent information
- They consist of data and behavior, bundled together to create abstractions
4
SLIDE 7
Objects
- Objects represent information
- They consist of data and behavior, bundled together to create abstractions
- Objects can represent things, but also properties, interactions, & processes
4
SLIDE 8
Objects
- Objects represent information
- They consist of data and behavior, bundled together to create abstractions
- Objects can represent things, but also properties, interactions, & processes
- A type of object is called a class; classes are first-class values in Python
4
SLIDE 9
Objects
- Objects represent information
- They consist of data and behavior, bundled together to create abstractions
- Objects can represent things, but also properties, interactions, & processes
- A type of object is called a class; classes are first-class values in Python
- Object-oriented programming:
4
SLIDE 10
Objects
- Objects represent information
- They consist of data and behavior, bundled together to create abstractions
- Objects can represent things, but also properties, interactions, & processes
- A type of object is called a class; classes are first-class values in Python
- Object-oriented programming:
- A metaphor for organizing large programs
4
SLIDE 11
Objects
- Objects represent information
- They consist of data and behavior, bundled together to create abstractions
- Objects can represent things, but also properties, interactions, & processes
- A type of object is called a class; classes are first-class values in Python
- Object-oriented programming:
- A metaphor for organizing large programs
- Special syntax that can improve the composition of programs
4
SLIDE 12
Objects
- Objects represent information
- They consist of data and behavior, bundled together to create abstractions
- Objects can represent things, but also properties, interactions, & processes
- A type of object is called a class; classes are first-class values in Python
- Object-oriented programming:
- A metaphor for organizing large programs
- Special syntax that can improve the composition of programs
- In Python, every value is an object
4
SLIDE 13
Objects
- Objects represent information
- They consist of data and behavior, bundled together to create abstractions
- Objects can represent things, but also properties, interactions, & processes
- A type of object is called a class; classes are first-class values in Python
- Object-oriented programming:
- A metaphor for organizing large programs
- Special syntax that can improve the composition of programs
- In Python, every value is an object
- All objects have attributes
4
SLIDE 14
Objects
- Objects represent information
- They consist of data and behavior, bundled together to create abstractions
- Objects can represent things, but also properties, interactions, & processes
- A type of object is called a class; classes are first-class values in Python
- Object-oriented programming:
- A metaphor for organizing large programs
- Special syntax that can improve the composition of programs
- In Python, every value is an object
- All objects have attributes
- A lot of data manipulation happens through object methods
4
SLIDE 15
Objects
- Objects represent information
- They consist of data and behavior, bundled together to create abstractions
- Objects can represent things, but also properties, interactions, & processes
- A type of object is called a class; classes are first-class values in Python
- Object-oriented programming:
- A metaphor for organizing large programs
- Special syntax that can improve the composition of programs
- In Python, every value is an object
- All objects have attributes
- A lot of data manipulation happens through object methods
- Functions do one thing; objects do many related things
4
SLIDE 16
Example: Strings
(Demo)
SLIDE 17
Representing Strings: the ASCII Standard
American Standard Code for Information Interchange
6
SLIDE 18
Representing Strings: the ASCII Standard
American Standard Code for Information Interchange 8 rows: 3 bits
6
SLIDE 19
Representing Strings: the ASCII Standard
American Standard Code for Information Interchange 8 rows: 3 bits 16 columns: 4 bits
6
SLIDE 20
Representing Strings: the ASCII Standard
American Standard Code for Information Interchange 8 rows: 3 bits 16 columns: 4 bits
- Layout was chosen to support sorting by character code
6
SLIDE 21
Representing Strings: the ASCII Standard
American Standard Code for Information Interchange 8 rows: 3 bits 16 columns: 4 bits
- Layout was chosen to support sorting by character code
- Rows indexed 2-5 are a useful 6-bit (64 element) subset
6
SLIDE 22
Representing Strings: the ASCII Standard
American Standard Code for Information Interchange 8 rows: 3 bits 16 columns: 4 bits
- Layout was chosen to support sorting by character code
- Rows indexed 2-5 are a useful 6-bit (64 element) subset
- Control characters were designed for transmission
6
SLIDE 23
Representing Strings: the ASCII Standard
American Standard Code for Information Interchange 8 rows: 3 bits 16 columns: 4 bits
- Layout was chosen to support sorting by character code
- Rows indexed 2-5 are a useful 6-bit (64 element) subset
- Control characters were designed for transmission
"Line feed" (\n)
6
SLIDE 24
Representing Strings: the ASCII Standard
American Standard Code for Information Interchange 8 rows: 3 bits 16 columns: 4 bits
- Layout was chosen to support sorting by character code
- Rows indexed 2-5 are a useful 6-bit (64 element) subset
- Control characters were designed for transmission
"Line feed" (\n) "Bell" (\a)
6
SLIDE 25
Representing Strings: the ASCII Standard
American Standard Code for Information Interchange 8 rows: 3 bits 16 columns: 4 bits
- Layout was chosen to support sorting by character code
- Rows indexed 2-5 are a useful 6-bit (64 element) subset
- Control characters were designed for transmission
"Line feed" (\n) "Bell" (\a)
6
(Demo)
SLIDE 26
Representing Strings: the Unicode Standard
7
SLIDE 27
Representing Strings: the Unicode Standard
http://ian-albert.com/unicode_chart/unichart-chinese.jpg
7
SLIDE 28
Representing Strings: the Unicode Standard
http://ian-albert.com/unicode_chart/unichart-chinese.jpg
- 109,000 characters
7
SLIDE 29
Representing Strings: the Unicode Standard
http://ian-albert.com/unicode_chart/unichart-chinese.jpg
- 109,000 characters
- 93 scripts (organized)
7
SLIDE 30
Representing Strings: the Unicode Standard
http://ian-albert.com/unicode_chart/unichart-chinese.jpg
- 109,000 characters
- 93 scripts (organized)
- Enumeration of character properties,
such as case
7
SLIDE 31
Representing Strings: the Unicode Standard
http://ian-albert.com/unicode_chart/unichart-chinese.jpg
- 109,000 characters
- 93 scripts (organized)
- Enumeration of character properties,
such as case
- Supports bidirectional display order
7
SLIDE 32
Representing Strings: the Unicode Standard
http://ian-albert.com/unicode_chart/unichart-chinese.jpg
- 109,000 characters
- 93 scripts (organized)
- Enumeration of character properties,
such as case
- Supports bidirectional display order
- A canonical name for every character
7
SLIDE 33
Representing Strings: the Unicode Standard
http://ian-albert.com/unicode_chart/unichart-chinese.jpg
- 109,000 characters
- 93 scripts (organized)
- Enumeration of character properties,
such as case
- Supports bidirectional display order
- A canonical name for every character
U+0058 LATIN CAPITAL LETTER X
7
SLIDE 34
Representing Strings: the Unicode Standard
http://ian-albert.com/unicode_chart/unichart-chinese.jpg
- 109,000 characters
- 93 scripts (organized)
- Enumeration of character properties,
such as case
- Supports bidirectional display order
- A canonical name for every character
U+0058 LATIN CAPITAL LETTER X U+263a WHITE SMILING FACE
7
SLIDE 35
Representing Strings: the Unicode Standard
http://ian-albert.com/unicode_chart/unichart-chinese.jpg
- 109,000 characters
- 93 scripts (organized)
- Enumeration of character properties,
such as case
- Supports bidirectional display order
- A canonical name for every character
U+0058 LATIN CAPITAL LETTER X U+263a WHITE SMILING FACE U+2639 WHITE FROWNING FACE
7
SLIDE 36
Representing Strings: the Unicode Standard
http://ian-albert.com/unicode_chart/unichart-chinese.jpg
- 109,000 characters
- 93 scripts (organized)
- Enumeration of character properties,
such as case
- Supports bidirectional display order
- A canonical name for every character
U+0058 LATIN CAPITAL LETTER X U+263a WHITE SMILING FACE U+2639 WHITE FROWNING FACE
'☺'
7
SLIDE 37
Representing Strings: the Unicode Standard
http://ian-albert.com/unicode_chart/unichart-chinese.jpg
- 109,000 characters
- 93 scripts (organized)
- Enumeration of character properties,
such as case
- Supports bidirectional display order
- A canonical name for every character
U+0058 LATIN CAPITAL LETTER X U+263a WHITE SMILING FACE U+2639 WHITE FROWNING FACE
'☺' '☹'
7
SLIDE 38
Representing Strings: the Unicode Standard
http://ian-albert.com/unicode_chart/unichart-chinese.jpg
- 109,000 characters
- 93 scripts (organized)
- Enumeration of character properties,
such as case
- Supports bidirectional display order
- A canonical name for every character
U+0058 LATIN CAPITAL LETTER X U+263a WHITE SMILING FACE U+2639 WHITE FROWNING FACE
'☺' '☹'
7
(Demo)
SLIDE 39
Mutation Operations
SLIDE 40
Some Objects Can Change
9
[Demo]
SLIDE 41
Some Objects Can Change
First example in the course of an object changing state
9
[Demo]
SLIDE 42
Some Objects Can Change
First example in the course of an object changing state The same object can change in value throughout the course of computation
9
[Demo]
SLIDE 43
Some Objects Can Change
First example in the course of an object changing state The same object can change in value throughout the course of computation
9
[Demo]
👷
same_person
SLIDE 44
Some Objects Can Change
First example in the course of an object changing state The same object can change in value throughout the course of computation
9
[Demo]
👷
BABY same_person
SLIDE 45
Some Objects Can Change
First example in the course of an object changing state The same object can change in value throughout the course of computation
9
[Demo]
👷
BABY same_person Unicode character name
SLIDE 46
Some Objects Can Change
First example in the course of an object changing state The same object can change in value throughout the course of computation
9
[Demo]
👨
GIRL same_person Unicode character name
SLIDE 47
Some Objects Can Change
First example in the course of an object changing state The same object can change in value throughout the course of computation
9
[Demo]
👨
GIRL jessica same_person Unicode character name
SLIDE 48
Some Objects Can Change
First example in the course of an object changing state The same object can change in value throughout the course of computation
9
[Demo]
👪
WOMAN jessica same_person Unicode character name
SLIDE 49
Some Objects Can Change
First example in the course of an object changing state The same object can change in value throughout the course of computation
9
[Demo]
👶
OLDER WOMAN jessica same_person Unicode character name
SLIDE 50
Some Objects Can Change
First example in the course of an object changing state The same object can change in value throughout the course of computation
9
[Demo]
👶
OLDER WOMAN jessica same_person Unicode character name All names that refer to the same object are affected by a mutation
SLIDE 51
Some Objects Can Change
First example in the course of an object changing state The same object can change in value throughout the course of computation
9
[Demo]
👶
OLDER WOMAN jessica same_person Unicode character name All names that refer to the same object are affected by a mutation Only objects of mutable types can change: lists & dictionaries
SLIDE 52
Some Objects Can Change
First example in the course of an object changing state The same object can change in value throughout the course of computation
9
[Demo]
👶
OLDER WOMAN jessica same_person Unicode character name All names that refer to the same object are affected by a mutation Only objects of mutable types can change: lists & dictionaries {Demo}
SLIDE 53
Mutation Can Happen Within a Function Call
A function can change the value of any object in its scope
10
SLIDE 54
Mutation Can Happen Within a Function Call
A function can change the value of any object in its scope
10
>>> four = [1, 2, 3, 4]
SLIDE 55
Mutation Can Happen Within a Function Call
A function can change the value of any object in its scope
10
>>> four = [1, 2, 3, 4] >>> len(four) 4
SLIDE 56
Mutation Can Happen Within a Function Call
A function can change the value of any object in its scope
10
>>> four = [1, 2, 3, 4] >>> len(four) 4 >>> mystery(four)
SLIDE 57
Mutation Can Happen Within a Function Call
A function can change the value of any object in its scope
10
>>> four = [1, 2, 3, 4] >>> len(four) 4 >>> mystery(four) >>> len(four) 2
SLIDE 58
Mutation Can Happen Within a Function Call
A function can change the value of any object in its scope
10
>>> four = [1, 2, 3, 4] >>> len(four) 4 >>> mystery(four) >>> len(four) 2 def mystery(s): s.pop() s.pop() Interactive Diagram
SLIDE 59
Mutation Can Happen Within a Function Call
A function can change the value of any object in its scope
10
>>> four = [1, 2, 3, 4] >>> len(four) 4 >>> mystery(four) >>> len(four) 2 def mystery(s): s.pop() s.pop() Interactive Diagram def mystery(s): s[2:] = []
- r
SLIDE 60
Mutation Can Happen Within a Function Call
A function can change the value of any object in its scope
10
>>> four = [1, 2, 3, 4] >>> len(four) 4 >>> mystery(four) >>> len(four) 2 >>> four = [1, 2, 3, 4] def mystery(s): s.pop() s.pop() Interactive Diagram def mystery(s): s[2:] = []
- r
SLIDE 61
Mutation Can Happen Within a Function Call
A function can change the value of any object in its scope
10
>>> four = [1, 2, 3, 4] >>> len(four) 4 >>> mystery(four) >>> len(four) 2 >>> four = [1, 2, 3, 4] >>> len(four) 4 def mystery(s): s.pop() s.pop() Interactive Diagram def mystery(s): s[2:] = []
- r
SLIDE 62
Mutation Can Happen Within a Function Call
A function can change the value of any object in its scope
10
>>> four = [1, 2, 3, 4] >>> len(four) 4 >>> mystery(four) >>> len(four) 2 >>> four = [1, 2, 3, 4] >>> len(four) 4 >>> another_mystery() # No arguments! def mystery(s): s.pop() s.pop() Interactive Diagram def mystery(s): s[2:] = []
- r
SLIDE 63
Mutation Can Happen Within a Function Call
A function can change the value of any object in its scope
10
>>> four = [1, 2, 3, 4] >>> len(four) 4 >>> mystery(four) >>> len(four) 2 >>> four = [1, 2, 3, 4] >>> len(four) 4 >>> another_mystery() # No arguments! >>> len(four) 2 def mystery(s): s.pop() s.pop() Interactive Diagram def mystery(s): s[2:] = []
- r
SLIDE 64
Mutation Can Happen Within a Function Call
A function can change the value of any object in its scope
10
>>> four = [1, 2, 3, 4] >>> len(four) 4 >>> mystery(four) >>> len(four) 2 >>> four = [1, 2, 3, 4] >>> len(four) 4 >>> another_mystery() # No arguments! >>> len(four) 2 def mystery(s): s.pop() s.pop() def another_mystery(): four.pop() four.pop() Interactive Diagram def mystery(s): s[2:] = []
- r
SLIDE 65
Tuples
(Demo)
SLIDE 66
Tuples are Immutable Sequences
12
SLIDE 67
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
SLIDE 68
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
>>> turtle = (1, 2, 3)
SLIDE 69
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
>>> turtle = (1, 2, 3) >>> ooze()
SLIDE 70
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
>>> turtle = (1, 2, 3) >>> ooze() >>> turtle
SLIDE 71
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
>>> turtle = (1, 2, 3) >>> ooze() >>> turtle (1, 2, 3)
SLIDE 72
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
>>> turtle = (1, 2, 3) >>> ooze() >>> turtle (1, 2, 3) >>> turtle = [1, 2, 3]
SLIDE 73
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
>>> turtle = (1, 2, 3) >>> ooze() >>> turtle (1, 2, 3) >>> turtle = [1, 2, 3] >>> ooze()
SLIDE 74
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
>>> turtle = (1, 2, 3) >>> ooze() >>> turtle (1, 2, 3) >>> turtle = [1, 2, 3] >>> ooze() >>> turtle
SLIDE 75
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
>>> turtle = (1, 2, 3) >>> ooze() >>> turtle (1, 2, 3) >>> turtle = [1, 2, 3] >>> ooze() >>> turtle ['Anything could be inside!']
SLIDE 76
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
>>> turtle = (1, 2, 3) >>> ooze() >>> turtle (1, 2, 3) >>> turtle = [1, 2, 3] >>> ooze() >>> turtle ['Anything could be inside!'] Next lecture: ooze can change turtle's binding
SLIDE 77
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
The value of an expression can change because of changes in names or objects >>> turtle = (1, 2, 3) >>> ooze() >>> turtle (1, 2, 3) >>> turtle = [1, 2, 3] >>> ooze() >>> turtle ['Anything could be inside!'] Next lecture: ooze can change turtle's binding
SLIDE 78
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
The value of an expression can change because of changes in names or objects >>> turtle = (1, 2, 3) >>> ooze() >>> turtle (1, 2, 3) >>> turtle = [1, 2, 3] >>> ooze() >>> turtle ['Anything could be inside!'] Name change: Next lecture: ooze can change turtle's binding
SLIDE 79
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
The value of an expression can change because of changes in names or objects >>> turtle = (1, 2, 3) >>> ooze() >>> turtle (1, 2, 3) >>> turtle = [1, 2, 3] >>> ooze() >>> turtle ['Anything could be inside!'] >>> x + x >>> x + x Name change: Next lecture: ooze can change turtle's binding
SLIDE 80
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
The value of an expression can change because of changes in names or objects >>> turtle = (1, 2, 3) >>> ooze() >>> turtle (1, 2, 3) >>> turtle = [1, 2, 3] >>> ooze() >>> turtle ['Anything could be inside!'] >>> x + x >>> x + x Name change: >>> x = 2 Next lecture: ooze can change turtle's binding
SLIDE 81
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
The value of an expression can change because of changes in names or objects >>> turtle = (1, 2, 3) >>> ooze() >>> turtle (1, 2, 3) >>> turtle = [1, 2, 3] >>> ooze() >>> turtle ['Anything could be inside!'] >>> x + x >>> x + x Name change: >>> x = 2 4 Next lecture: ooze can change turtle's binding
SLIDE 82
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
The value of an expression can change because of changes in names or objects >>> turtle = (1, 2, 3) >>> ooze() >>> turtle (1, 2, 3) >>> turtle = [1, 2, 3] >>> ooze() >>> turtle ['Anything could be inside!'] >>> x + x >>> x + x Name change: >>> x = 2 4 >>> x = 3 Next lecture: ooze can change turtle's binding
SLIDE 83
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
The value of an expression can change because of changes in names or objects >>> turtle = (1, 2, 3) >>> ooze() >>> turtle (1, 2, 3) >>> turtle = [1, 2, 3] >>> ooze() >>> turtle ['Anything could be inside!'] >>> x + x >>> x + x Name change: >>> x = 2 4 >>> x = 3 6 Next lecture: ooze can change turtle's binding
SLIDE 84
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
The value of an expression can change because of changes in names or objects >>> turtle = (1, 2, 3) >>> ooze() >>> turtle (1, 2, 3) >>> turtle = [1, 2, 3] >>> ooze() >>> turtle ['Anything could be inside!'] >>> x + x >>> x + x Name change: Object mutation: >>> x = 2 4 >>> x = 3 6 Next lecture: ooze can change turtle's binding
SLIDE 85
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
The value of an expression can change because of changes in names or objects >>> turtle = (1, 2, 3) >>> ooze() >>> turtle (1, 2, 3) >>> turtle = [1, 2, 3] >>> ooze() >>> turtle ['Anything could be inside!'] >>> x + x >>> x + x Name change: Object mutation: >>> x = 2 4 >>> x = 3 6 >>> x + x >>> x + x Next lecture: ooze can change turtle's binding
SLIDE 86
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
The value of an expression can change because of changes in names or objects >>> turtle = (1, 2, 3) >>> ooze() >>> turtle (1, 2, 3) >>> turtle = [1, 2, 3] >>> ooze() >>> turtle ['Anything could be inside!'] >>> x + x >>> x + x Name change: Object mutation: >>> x = 2 4 >>> x = 3 6 >>> x = [1, 2] >>> x + x >>> x + x Next lecture: ooze can change turtle's binding
SLIDE 87
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
The value of an expression can change because of changes in names or objects >>> turtle = (1, 2, 3) >>> ooze() >>> turtle (1, 2, 3) >>> turtle = [1, 2, 3] >>> ooze() >>> turtle ['Anything could be inside!'] >>> x + x >>> x + x Name change: Object mutation: >>> x = 2 4 >>> x = 3 6 >>> x = [1, 2] [1, 2, 1, 2] >>> x + x >>> x + x Next lecture: ooze can change turtle's binding
SLIDE 88
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
The value of an expression can change because of changes in names or objects >>> turtle = (1, 2, 3) >>> ooze() >>> turtle (1, 2, 3) >>> turtle = [1, 2, 3] >>> ooze() >>> turtle ['Anything could be inside!'] >>> x + x >>> x + x Name change: Object mutation: >>> x = 2 4 >>> x = 3 6 >>> x = [1, 2] [1, 2, 1, 2] >>> x.append(3) >>> x + x >>> x + x Next lecture: ooze can change turtle's binding
SLIDE 89
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
The value of an expression can change because of changes in names or objects >>> turtle = (1, 2, 3) >>> ooze() >>> turtle (1, 2, 3) >>> turtle = [1, 2, 3] >>> ooze() >>> turtle ['Anything could be inside!'] >>> x + x >>> x + x Name change: Object mutation: >>> x = 2 4 >>> x = 3 6 >>> x = [1, 2] [1, 2, 1, 2] >>> x.append(3) [1, 2, 3, 1, 2, 3] >>> x + x >>> x + x Next lecture: ooze can change turtle's binding
SLIDE 90
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
The value of an expression can change because of changes in names or objects An immutable sequence may still change if it contains a mutable value as an element >>> turtle = (1, 2, 3) >>> ooze() >>> turtle (1, 2, 3) >>> turtle = [1, 2, 3] >>> ooze() >>> turtle ['Anything could be inside!'] >>> x + x >>> x + x Name change: Object mutation: >>> x = 2 4 >>> x = 3 6 >>> x = [1, 2] [1, 2, 1, 2] >>> x.append(3) [1, 2, 3, 1, 2, 3] >>> x + x >>> x + x Next lecture: ooze can change turtle's binding
SLIDE 91
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
The value of an expression can change because of changes in names or objects An immutable sequence may still change if it contains a mutable value as an element >>> turtle = (1, 2, 3) >>> ooze() >>> turtle (1, 2, 3) >>> turtle = [1, 2, 3] >>> ooze() >>> turtle ['Anything could be inside!'] >>> x + x >>> x + x Name change: Object mutation: >>> x = 2 4 >>> x = 3 6 >>> x = [1, 2] [1, 2, 1, 2] >>> x.append(3) [1, 2, 3, 1, 2, 3] >>> s = ([1, 2], 3) >>> x + x >>> x + x Next lecture: ooze can change turtle's binding
SLIDE 92
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
The value of an expression can change because of changes in names or objects An immutable sequence may still change if it contains a mutable value as an element >>> turtle = (1, 2, 3) >>> ooze() >>> turtle (1, 2, 3) >>> turtle = [1, 2, 3] >>> ooze() >>> turtle ['Anything could be inside!'] >>> x + x >>> x + x Name change: Object mutation: >>> x = 2 4 >>> x = 3 6 >>> x = [1, 2] [1, 2, 1, 2] >>> x.append(3) [1, 2, 3, 1, 2, 3] >>> s = ([1, 2], 3) >>> s[0] = 4 >>> x + x >>> x + x Next lecture: ooze can change turtle's binding
SLIDE 93
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
The value of an expression can change because of changes in names or objects An immutable sequence may still change if it contains a mutable value as an element >>> turtle = (1, 2, 3) >>> ooze() >>> turtle (1, 2, 3) >>> turtle = [1, 2, 3] >>> ooze() >>> turtle ['Anything could be inside!'] >>> x + x >>> x + x Name change: Object mutation: >>> x = 2 4 >>> x = 3 6 >>> x = [1, 2] [1, 2, 1, 2] >>> x.append(3) [1, 2, 3, 1, 2, 3] >>> s = ([1, 2], 3) >>> s[0] = 4 ERROR >>> x + x >>> x + x Next lecture: ooze can change turtle's binding
SLIDE 94
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
The value of an expression can change because of changes in names or objects An immutable sequence may still change if it contains a mutable value as an element >>> turtle = (1, 2, 3) >>> ooze() >>> turtle (1, 2, 3) >>> turtle = [1, 2, 3] >>> ooze() >>> turtle ['Anything could be inside!'] >>> x + x >>> x + x Name change: Object mutation: >>> x = 2 4 >>> x = 3 6 >>> x = [1, 2] [1, 2, 1, 2] >>> x.append(3) [1, 2, 3, 1, 2, 3] >>> s = ([1, 2], 3) >>> s[0] = 4 ERROR >>> s = ([1, 2], 3) >>> x + x >>> x + x Next lecture: ooze can change turtle's binding
SLIDE 95
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
The value of an expression can change because of changes in names or objects An immutable sequence may still change if it contains a mutable value as an element >>> turtle = (1, 2, 3) >>> ooze() >>> turtle (1, 2, 3) >>> turtle = [1, 2, 3] >>> ooze() >>> turtle ['Anything could be inside!'] >>> x + x >>> x + x Name change: Object mutation: >>> x = 2 4 >>> x = 3 6 >>> x = [1, 2] [1, 2, 1, 2] >>> x.append(3) [1, 2, 3, 1, 2, 3] >>> s = ([1, 2], 3) >>> s[0] = 4 ERROR >>> s = ([1, 2], 3) >>> s[0][0] = 4 >>> x + x >>> x + x Next lecture: ooze can change turtle's binding
SLIDE 96
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
The value of an expression can change because of changes in names or objects An immutable sequence may still change if it contains a mutable value as an element >>> turtle = (1, 2, 3) >>> ooze() >>> turtle (1, 2, 3) >>> turtle = [1, 2, 3] >>> ooze() >>> turtle ['Anything could be inside!'] >>> x + x >>> x + x Name change: Object mutation: >>> x = 2 4 >>> x = 3 6 >>> x = [1, 2] [1, 2, 1, 2] >>> x.append(3) [1, 2, 3, 1, 2, 3] >>> s = ([1, 2], 3) >>> s[0] = 4 ERROR >>> s = ([1, 2], 3) >>> s[0][0] = 4 >>> s >>> x + x >>> x + x Next lecture: ooze can change turtle's binding
SLIDE 97
Tuples are Immutable Sequences
Immutable values are protected from mutation
12
The value of an expression can change because of changes in names or objects An immutable sequence may still change if it contains a mutable value as an element >>> turtle = (1, 2, 3) >>> ooze() >>> turtle (1, 2, 3) >>> turtle = [1, 2, 3] >>> ooze() >>> turtle ['Anything could be inside!'] >>> x + x >>> x + x Name change: Object mutation: >>> x = 2 4 >>> x = 3 6 >>> x = [1, 2] [1, 2, 1, 2] >>> x.append(3) [1, 2, 3, 1, 2, 3] >>> s = ([1, 2], 3) >>> s[0] = 4 ERROR >>> s = ([1, 2], 3) >>> s[0][0] = 4 >>> s ([4, 2], 3) >>> x + x >>> x + x Next lecture: ooze can change turtle's binding
SLIDE 98
Mutation
SLIDE 99
Sameness and Change
14
SLIDE 100
Sameness and Change
- As long as we never modify objects, a compound object is just the totality of its pieces
14
SLIDE 101
Sameness and Change
- As long as we never modify objects, a compound object is just the totality of its pieces
- A rational number is just its numerator and denominator
14
SLIDE 102
Sameness and Change
- As long as we never modify objects, a compound object is just the totality of its pieces
- A rational number is just its numerator and denominator
- This view is no longer valid in the presence of change
14
SLIDE 103
Sameness and Change
- As long as we never modify objects, a compound object is just the totality of its pieces
- A rational number is just its numerator and denominator
- This view is no longer valid in the presence of change
- A compound data object has an "identity" in addition to the pieces of which it is composed
14
SLIDE 104
Sameness and Change
- As long as we never modify objects, a compound object is just the totality of its pieces
- A rational number is just its numerator and denominator
- This view is no longer valid in the presence of change
- A compound data object has an "identity" in addition to the pieces of which it is composed
- A list is still "the same" list even if we change its contents
14
SLIDE 105
Sameness and Change
- As long as we never modify objects, a compound object is just the totality of its pieces
- A rational number is just its numerator and denominator
- This view is no longer valid in the presence of change
- A compound data object has an "identity" in addition to the pieces of which it is composed
- A list is still "the same" list even if we change its contents
14
>>> a = [10]
SLIDE 106
Sameness and Change
- As long as we never modify objects, a compound object is just the totality of its pieces
- A rational number is just its numerator and denominator
- This view is no longer valid in the presence of change
- A compound data object has an "identity" in addition to the pieces of which it is composed
- A list is still "the same" list even if we change its contents
14
>>> a = [10] >>> b = a
SLIDE 107
Sameness and Change
- As long as we never modify objects, a compound object is just the totality of its pieces
- A rational number is just its numerator and denominator
- This view is no longer valid in the presence of change
- A compound data object has an "identity" in addition to the pieces of which it is composed
- A list is still "the same" list even if we change its contents
14
>>> a = [10] >>> b = a >>> a == b True
SLIDE 108
Sameness and Change
- As long as we never modify objects, a compound object is just the totality of its pieces
- A rational number is just its numerator and denominator
- This view is no longer valid in the presence of change
- A compound data object has an "identity" in addition to the pieces of which it is composed
- A list is still "the same" list even if we change its contents
14
>>> a = [10] >>> b = a >>> a == b True >>> a.append(20)
SLIDE 109
Sameness and Change
- As long as we never modify objects, a compound object is just the totality of its pieces
- A rational number is just its numerator and denominator
- This view is no longer valid in the presence of change
- A compound data object has an "identity" in addition to the pieces of which it is composed
- A list is still "the same" list even if we change its contents
14
>>> a = [10] >>> b = a >>> a == b True >>> a.append(20) >>> a == b True
SLIDE 110
Sameness and Change
- As long as we never modify objects, a compound object is just the totality of its pieces
- A rational number is just its numerator and denominator
- This view is no longer valid in the presence of change
- A compound data object has an "identity" in addition to the pieces of which it is composed
- A list is still "the same" list even if we change its contents
14
>>> a = [10] >>> b = a >>> a == b True >>> a.append(20) >>> a == b True >>> a [10, 20]
SLIDE 111
Sameness and Change
- As long as we never modify objects, a compound object is just the totality of its pieces
- A rational number is just its numerator and denominator
- This view is no longer valid in the presence of change
- A compound data object has an "identity" in addition to the pieces of which it is composed
- A list is still "the same" list even if we change its contents
14
>>> a = [10] >>> b = a >>> a == b True >>> a.append(20) >>> a == b True >>> a [10, 20] >>> b [10, 20]
SLIDE 112
Sameness and Change
- As long as we never modify objects, a compound object is just the totality of its pieces
- A rational number is just its numerator and denominator
- This view is no longer valid in the presence of change
- A compound data object has an "identity" in addition to the pieces of which it is composed
- A list is still "the same" list even if we change its contents
- Conversely, we could have two lists that happen to have the same contents, but are different
14
>>> a = [10] >>> b = a >>> a == b True >>> a.append(20) >>> a == b True >>> a [10, 20] >>> b [10, 20]
SLIDE 113
Sameness and Change
- As long as we never modify objects, a compound object is just the totality of its pieces
- A rational number is just its numerator and denominator
- This view is no longer valid in the presence of change
- A compound data object has an "identity" in addition to the pieces of which it is composed
- A list is still "the same" list even if we change its contents
- Conversely, we could have two lists that happen to have the same contents, but are different
14
>>> a = [10] >>> a = [10] >>> b = a >>> a == b True >>> a.append(20) >>> a == b True >>> a [10, 20] >>> b [10, 20]
SLIDE 114
Sameness and Change
- As long as we never modify objects, a compound object is just the totality of its pieces
- A rational number is just its numerator and denominator
- This view is no longer valid in the presence of change
- A compound data object has an "identity" in addition to the pieces of which it is composed
- A list is still "the same" list even if we change its contents
- Conversely, we could have two lists that happen to have the same contents, but are different
14
>>> a = [10] >>> b = [10] >>> a = [10] >>> b = a >>> a == b True >>> a.append(20) >>> a == b True >>> a [10, 20] >>> b [10, 20]
SLIDE 115
Sameness and Change
- As long as we never modify objects, a compound object is just the totality of its pieces
- A rational number is just its numerator and denominator
- This view is no longer valid in the presence of change
- A compound data object has an "identity" in addition to the pieces of which it is composed
- A list is still "the same" list even if we change its contents
- Conversely, we could have two lists that happen to have the same contents, but are different
14
>>> a = [10] >>> b = [10] >>> a == b True >>> a = [10] >>> b = a >>> a == b True >>> a.append(20) >>> a == b True >>> a [10, 20] >>> b [10, 20]
SLIDE 116
Sameness and Change
- As long as we never modify objects, a compound object is just the totality of its pieces
- A rational number is just its numerator and denominator
- This view is no longer valid in the presence of change
- A compound data object has an "identity" in addition to the pieces of which it is composed
- A list is still "the same" list even if we change its contents
- Conversely, we could have two lists that happen to have the same contents, but are different
14
>>> a = [10] >>> b = [10] >>> a == b True >>> b.append(20) >>> a = [10] >>> b = a >>> a == b True >>> a.append(20) >>> a == b True >>> a [10, 20] >>> b [10, 20]
SLIDE 117
Sameness and Change
- As long as we never modify objects, a compound object is just the totality of its pieces
- A rational number is just its numerator and denominator
- This view is no longer valid in the presence of change
- A compound data object has an "identity" in addition to the pieces of which it is composed
- A list is still "the same" list even if we change its contents
- Conversely, we could have two lists that happen to have the same contents, but are different
14
>>> a = [10] >>> b = [10] >>> a == b True >>> b.append(20) >>> a [10] >>> a = [10] >>> b = a >>> a == b True >>> a.append(20) >>> a == b True >>> a [10, 20] >>> b [10, 20]
SLIDE 118
Sameness and Change
- As long as we never modify objects, a compound object is just the totality of its pieces
- A rational number is just its numerator and denominator
- This view is no longer valid in the presence of change
- A compound data object has an "identity" in addition to the pieces of which it is composed
- A list is still "the same" list even if we change its contents
- Conversely, we could have two lists that happen to have the same contents, but are different
14
>>> a = [10] >>> b = [10] >>> a == b True >>> b.append(20) >>> a [10] >>> b [10, 20] >>> a = [10] >>> b = a >>> a == b True >>> a.append(20) >>> a == b True >>> a [10, 20] >>> b [10, 20]
SLIDE 119
Sameness and Change
- As long as we never modify objects, a compound object is just the totality of its pieces
- A rational number is just its numerator and denominator
- This view is no longer valid in the presence of change
- A compound data object has an "identity" in addition to the pieces of which it is composed
- A list is still "the same" list even if we change its contents
- Conversely, we could have two lists that happen to have the same contents, but are different
14
>>> a = [10] >>> b = [10] >>> a == b True >>> b.append(20) >>> a [10] >>> b [10, 20] >>> a == b False >>> a = [10] >>> b = a >>> a == b True >>> a.append(20) >>> a == b True >>> a [10, 20] >>> b [10, 20]
SLIDE 120
Identity Operators
15
SLIDE 121
Identity Operators
Identity <exp0> is <exp1> evaluates to True if both <exp0> and <exp1> evaluate to the same object
15
SLIDE 122
Identity Operators
Identity <exp0> is <exp1> evaluates to True if both <exp0> and <exp1> evaluate to the same object Equality <exp0> == <exp1> evaluates to True if both <exp0> and <exp1> evaluate to equal values
15
SLIDE 123
Identity Operators
Identity <exp0> is <exp1> evaluates to True if both <exp0> and <exp1> evaluate to the same object Equality <exp0> == <exp1> evaluates to True if both <exp0> and <exp1> evaluate to equal values Identical objects are always equal values
15
SLIDE 124
Identity Operators
Identity <exp0> is <exp1> evaluates to True if both <exp0> and <exp1> evaluate to the same object Equality <exp0> == <exp1> evaluates to True if both <exp0> and <exp1> evaluate to equal values Identical objects are always equal values
15
(Demo)
SLIDE 125
Mutable Default Arguments are Dangerous
16
SLIDE 126
Mutable Default Arguments are Dangerous
A default argument value is part of a function value, not generated by a call
16
SLIDE 127
Mutable Default Arguments are Dangerous
A default argument value is part of a function value, not generated by a call
16
>>> def f(s=[]): ... s.append(3) ... return len(s) ...
SLIDE 128
Mutable Default Arguments are Dangerous
A default argument value is part of a function value, not generated by a call
16
>>> def f(s=[]): ... s.append(3) ... return len(s) ... >>> f() 1
SLIDE 129
Mutable Default Arguments are Dangerous
A default argument value is part of a function value, not generated by a call
16
>>> def f(s=[]): ... s.append(3) ... return len(s) ... >>> f() 1 >>> f() 2
SLIDE 130
Mutable Default Arguments are Dangerous
A default argument value is part of a function value, not generated by a call
16
>>> def f(s=[]): ... s.append(3) ... return len(s) ... >>> f() 1 >>> f() 2 >>> f() 3
SLIDE 131
Mutable Default Arguments are Dangerous
A default argument value is part of a function value, not generated by a call
16
Interactive Diagram >>> def f(s=[]): ... s.append(3) ... return len(s) ... >>> f() 1 >>> f() 2 >>> f() 3
SLIDE 132
Mutable Default Arguments are Dangerous
A default argument value is part of a function value, not generated by a call
16
Interactive Diagram >>> def f(s=[]): ... s.append(3) ... return len(s) ... >>> f() 1 >>> f() 2 >>> f() 3 Each time the function is called, s is bound to the same value!