Mutable Values Announcements Objects (Demo) Objects 4 Objects - - PowerPoint PPT Presentation

Mutable Values

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

• Objects represent information
• They consist of data and behavior, bundled together to create abstractions
• Objects can represent things, but also properties, interactions, & processes

4

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

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

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

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

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

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

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

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

Example: Strings

(Demo)

Representing Strings: the ASCII Standard

American Standard Code for Information Interchange

6

Representing Strings: the ASCII Standard

American Standard Code for Information Interchange 8 rows: 3 bits

6

Representing Strings: the ASCII Standard

American Standard Code for Information Interchange 8 rows: 3 bits

6

0 0 0 0 0 1 0 1 0 0 1 1 1 0 0 1 0 1 1 1 0 1 1 1

Representing Strings: the ASCII Standard

American Standard Code for Information Interchange 8 rows: 3 bits 16 columns: 4 bits

6

0 0 0 0 0 1 0 1 0 0 1 1 1 0 0 1 0 1 1 1 0 1 1 1

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

0 0 0 0 0 1 0 1 0 0 1 1 1 0 0 1 0 1 1 1 0 1 1 1

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

0 0 0 0 0 1 0 1 0 0 1 1 1 0 0 1 0 1 1 1 0 1 1 1

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

0 0 0 0 0 1 0 1 0 0 1 1 1 0 0 1 0 1 1 1 0 1 1 1

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

0 0 0 0 0 1 0 1 0 0 1 1 1 0 0 1 0 1 1 1 0 1 1 1

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

0 0 0 0 0 1 0 1 0 0 1 1 1 0 0 1 0 1 1 1 0 1 1 1

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)

0 0 0 0 0 1 0 1 0 0 1 1 1 0 0 1 0 1 1 1 0 1 1 1

Representing Strings: the Unicode Standard

7

Representing Strings: the Unicode Standard

http://ian-albert.com/unicode_chart/unichart-chinese.jpg

7

Representing Strings: the Unicode Standard

http://ian-albert.com/unicode_chart/unichart-chinese.jpg

• 137,994 characters in Unicode 12.1

7

Representing Strings: the Unicode Standard

http://ian-albert.com/unicode_chart/unichart-chinese.jpg

• 137,994 characters in Unicode 12.1
• 150 scripts (organized)

7

Representing Strings: the Unicode Standard

http://ian-albert.com/unicode_chart/unichart-chinese.jpg

• 137,994 characters in Unicode 12.1
• 150 scripts (organized)
• Enumeration of character properties,

such as case

7

Representing Strings: the Unicode Standard

http://ian-albert.com/unicode_chart/unichart-chinese.jpg

• 137,994 characters in Unicode 12.1
• 150 scripts (organized)
• Enumeration of character properties,

such as case

• Supports bidirectional display order

7

Representing Strings: the Unicode Standard

http://ian-albert.com/unicode_chart/unichart-chinese.jpg

• 137,994 characters in Unicode 12.1
• 150 scripts (organized)
• Enumeration of character properties,

such as case

• Supports bidirectional display order
• A canonical name for every character

7

Representing Strings: the Unicode Standard

http://ian-albert.com/unicode_chart/unichart-chinese.jpg

• 137,994 characters in Unicode 12.1
• 150 scripts (organized)
• Enumeration of character properties,

such as case

• Supports bidirectional display order
• A canonical name for every character

LATIN CAPITAL LETTER A

7

Representing Strings: the Unicode Standard

http://ian-albert.com/unicode_chart/unichart-chinese.jpg

• 137,994 characters in Unicode 12.1
• 150 scripts (organized)
• Enumeration of character properties,

such as case

• Supports bidirectional display order
• A canonical name for every character

LATIN CAPITAL LETTER A DIE FACE-6

7

Representing Strings: the Unicode Standard

http://ian-albert.com/unicode_chart/unichart-chinese.jpg

• 137,994 characters in Unicode 12.1
• 150 scripts (organized)
• Enumeration of character properties,

such as case

• Supports bidirectional display order
• A canonical name for every character

LATIN CAPITAL LETTER A DIE FACE-6 EIGHTH NOTE

7

Representing Strings: the Unicode Standard

http://ian-albert.com/unicode_chart/unichart-chinese.jpg

• 137,994 characters in Unicode 12.1
• 150 scripts (organized)
• Enumeration of character properties,

such as case

• Supports bidirectional display order
• A canonical name for every character

LATIN CAPITAL LETTER A DIE FACE-6 EIGHTH NOTE

'⚅'

7

Representing Strings: the Unicode Standard

http://ian-albert.com/unicode_chart/unichart-chinese.jpg

• 137,994 characters in Unicode 12.1
• 150 scripts (organized)
• Enumeration of character properties,

such as case

• Supports bidirectional display order
• A canonical name for every character

LATIN CAPITAL LETTER A DIE FACE-6 EIGHTH NOTE

'⚅' '♪'

7

Representing Strings: the Unicode Standard

http://ian-albert.com/unicode_chart/unichart-chinese.jpg

• 137,994 characters in Unicode 12.1
• 150 scripts (organized)
• Enumeration of character properties,

such as case

• Supports bidirectional display order
• A canonical name for every character

LATIN CAPITAL LETTER A DIE FACE-6 EIGHTH NOTE

'⚅' '♪'

7

(Demo)

Mutation Operations

Some Objects Can Change

9

[Demo]

Some Objects Can Change

First example in the course of an object changing state

9

[Demo]

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]

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

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

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

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

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

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

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

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

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

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}

Mutation Can Happen Within a Function Call

A function can change the value of any object in its scope

10

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]

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

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)

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

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()

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()

def mystery(s): s[2:] = []

• r

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()

def mystery(s): s[2:] = []

• r

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()

def mystery(s): s[2:] = []

• r

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()

def mystery(s): s[2:] = []

• r

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 mystery(s): s[2:] = []

• r

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()

def mystery(s): s[2:] = []

• r

Tuples

(Demo)

Tuples are Immutable Sequences

12

Tuples are Immutable Sequences

Immutable values are protected from mutation

12

Tuples are Immutable Sequences

Immutable values are protected from mutation

12

>>> turtle = (1, 2, 3)

Tuples are Immutable Sequences

Immutable values are protected from mutation

12

>>> turtle = (1, 2, 3) >>> ooze()

Tuples are Immutable Sequences

Immutable values are protected from mutation

12

>>> turtle = (1, 2, 3) >>> ooze() >>> turtle

Tuples are Immutable Sequences

Immutable values are protected from mutation

12

>>> turtle = (1, 2, 3) >>> ooze() >>> turtle (1, 2, 3)

Tuples are Immutable Sequences

Immutable values are protected from mutation

12

>>> turtle = (1, 2, 3) >>> ooze() >>> turtle (1, 2, 3) >>> turtle = [1, 2, 3]

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()

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

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!']

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Mutation

Sameness and Change

14

Sameness and Change

• As long as we never modify objects, a compound object is just the totality of its pieces

14

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

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

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

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

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]

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

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

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)

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 [10, 20]

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 [10, 20] >>> b [10, 20]

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 [10, 20] >>> b [10, 20] >>> a == b True

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 [10, 20] >>> b [10, 20] >>> a == b True

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 [10, 20] >>> b [10, 20] >>> a == b True

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 [10, 20] >>> b [10, 20] >>> a == b True

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 [10, 20] >>> b [10, 20] >>> a == b True

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 [10, 20] >>> b [10, 20] >>> a == b True

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 [10, 20] >>> b [10, 20] >>> a == b True

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 [10, 20] >>> b [10, 20] >>> a == b True

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 [10, 20] >>> b [10, 20] >>> a == b True

Identity Operators

15

Identity Operators

Identity <exp0> is <exp1> evaluates to True if both <exp0> and <exp1> evaluate to the same object

15

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

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

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)

Mutable Default Arguments are Dangerous

16

Mutable Default Arguments are Dangerous

A default argument value is part of a function value, not generated by a call

16

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) ...

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

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

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

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

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 Each time the function is called, s is bound to the same value!

Lists

Lists in Environment Diagrams

18

Lists in Environment Diagrams

Assume that before each example below we execute: s = [2, 3] t = [5, 6]

18

Lists in Environment Diagrams

Assume that before each example below we execute: s = [2, 3] t = [5, 6]

18

Operation

Lists in Environment Diagrams

Assume that before each example below we execute: s = [2, 3] t = [5, 6]

18

Operation Example

Lists in Environment Diagrams

Assume that before each example below we execute: s = [2, 3] t = [5, 6]

18

Operation Example Result

Lists in Environment Diagrams

Assume that before each example below we execute: s = [2, 3] t = [5, 6]

18

Operation Example Result append adds one element to a list

Lists in Environment Diagrams

Assume that before each example below we execute: s = [2, 3] t = [5, 6]

18

Operation Example Result append adds one element to a list s.append(t) t = 0

Lists in Environment Diagrams

Assume that before each example below we execute: s = [2, 3] t = [5, 6]

18

Operation Example Result append adds one element to a list s.append(t) t = 0

Global

Lists in Environment Diagrams

Assume that before each example below we execute: s = [2, 3] t = [5, 6]

18

Operation Example Result append adds one element to a list s.append(t) t = 0

Global s list 1

2

t

3

list 1

5 6

Lists in Environment Diagrams

Assume that before each example below we execute: s = [2, 3] t = [5, 6]

18

Operation Example Result append adds one element to a list s.append(t) t = 0

Global s list 1

2

t

3

list 1

5 6

2

Lists in Environment Diagrams

Assume that before each example below we execute: s = [2, 3] t = [5, 6]

18

Operation Example Result append adds one element to a list s.append(t) t = 0

Global s list 1

2

t

3

list 1

5 6

2

Lists in Environment Diagrams

Assume that before each example below we execute: s = [2, 3] t = [5, 6]

18

Operation Example Result append adds one element to a list s.append(t) t = 0 s → [2, 3, [5, 6]] t → 0

Global s list 1

2

t

3

list 1

5 6

2

Lists in Environment Diagrams

Assume that before each example below we execute: s = [2, 3] t = [5, 6]

18

Operation Example Result append adds one element to a list s.append(t) t = 0 s → [2, 3, [5, 6]] t → 0

Global s list 1

2

t

3

list 1

5 6

Lists in Environment Diagrams

Assume that before each example below we execute: s = [2, 3] t = [5, 6]

18

Operation Example Result append adds one element to a list s.append(t) t = 0 s → [2, 3, [5, 6]] t → 0 extend adds all elements in one list to another list

Global s list 1

2

t

3

list 1

5 6

Lists in Environment Diagrams

Assume that before each example below we execute: s = [2, 3] t = [5, 6]

18

Operation Example Result append adds one element to a list s.append(t) t = 0 s → [2, 3, [5, 6]] t → 0 extend adds all elements in one list to another list s.extend(t) t[1] = 0

Global s list 1

2

t

3

list 1

5 6

Lists in Environment Diagrams

Assume that before each example below we execute: s = [2, 3] t = [5, 6]

18

Operation Example Result append adds one element to a list s.append(t) t = 0 s → [2, 3, [5, 6]] t → 0 extend adds all elements in one list to another list s.extend(t) t[1] = 0

Global s list 1

2

t

3

list 1

5 6

2 3

5 6

Lists in Environment Diagrams

Assume that before each example below we execute: s = [2, 3] t = [5, 6]

18

Operation Example Result append adds one element to a list s.append(t) t = 0 s → [2, 3, [5, 6]] t → 0 extend adds all elements in one list to another list s.extend(t) t[1] = 0

Global s list 1

2

t

3

list 1

5 6

2 3

5 6

Lists in Environment Diagrams

Assume that before each example below we execute: s = [2, 3] t = [5, 6]

18

Operation Example Result append adds one element to a list s.append(t) t = 0 s → [2, 3, [5, 6]] t → 0 extend adds all elements in one list to another list s.extend(t) t[1] = 0 s → [2, 3, 5, 6] t → [5, 0]

Global s list 1

2

t

3

list 1

5 6

2 3

5 6

Lists in Environment Diagrams

Assume that before each example below we execute: s = [2, 3] t = [5, 6]

18

Operation Example Result append adds one element to a list s.append(t) t = 0 s → [2, 3, [5, 6]] t → 0 extend adds all elements in one list to another list s.extend(t) t[1] = 0 s → [2, 3, 5, 6] t → [5, 0]

Global s list 1

2

t

3

list 1

5 6

Lists in Environment Diagrams

Assume that before each example below we execute: s = [2, 3] t = [5, 6]

18

Operation Example Result append adds one element to a list s.append(t) t = 0 s → [2, 3, [5, 6]] t → 0 extend adds all elements in one list to another list s.extend(t) t[1] = 0 s → [2, 3, 5, 6] t → [5, 0] addition & slicing create new lists containing existing elements

Global s list 1

2

t

3

list 1

5 6

Lists in Environment Diagrams

Assume that before each example below we execute: s = [2, 3] t = [5, 6]

18

Operation Example Result append adds one element to a list s.append(t) t = 0 s → [2, 3, [5, 6]] t → 0 extend adds all elements in one list to another list s.extend(t) t[1] = 0 s → [2, 3, 5, 6] t → [5, 0] addition & slicing create new lists containing existing elements a = s + [t] b = a[1:] a[1] = 9 b[1][1] = 0

Global s list 1

2

t

3

list 1

5 6

Lists in Environment Diagrams

Assume that before each example below we execute: s = [2, 3] t = [5, 6]

18

Operation Example Result append adds one element to a list s.append(t) t = 0 s → [2, 3, [5, 6]] t → 0 extend adds all elements in one list to another list s.extend(t) t[1] = 0 s → [2, 3, 5, 6] t → [5, 0] addition & slicing create new lists containing existing elements a = s + [t] b = a[1:] a[1] = 9 b[1][1] = 0

Global s list 1

2

t

3

list 1

5 6

list

Lists in Environment Diagrams

Assume that before each example below we execute: s = [2, 3] t = [5, 6]

18

Operation Example Result append adds one element to a list s.append(t) t = 0 s → [2, 3, [5, 6]] t → 0 extend adds all elements in one list to another list s.extend(t) t[1] = 0 s → [2, 3, 5, 6] t → [5, 0] addition & slicing create new lists containing existing elements a = s + [t] b = a[1:] a[1] = 9 b[1][1] = 0

Global s list 1

2

t

3

list 1

5 6

list 1

2 3

2 list

Lists in Environment Diagrams

Assume that before each example below we execute: s = [2, 3] t = [5, 6]

18

Operation Example Result append adds one element to a list s.append(t) t = 0 s → [2, 3, [5, 6]] t → 0 extend adds all elements in one list to another list s.extend(t) t[1] = 0 s → [2, 3, 5, 6] t → [5, 0] addition & slicing create new lists containing existing elements a = s + [t] b = a[1:] a[1] = 9 b[1][1] = 0

Global s list 1

2

t

3

list 1

5 6

list 1

2 3

2 a list

Lists in Environment Diagrams

Assume that before each example below we execute: s = [2, 3] t = [5, 6]

18

Operation Example Result append adds one element to a list s.append(t) t = 0 s → [2, 3, [5, 6]] t → 0 extend adds all elements in one list to another list s.extend(t) t[1] = 0 s → [2, 3, 5, 6] t → [5, 0] addition & slicing create new lists containing existing elements a = s + [t] b = a[1:] a[1] = 9 b[1][1] = 0

Global s list 1

2

t

3

list 1

5 6

list 1

2 3

2 a

Lists in Environment Diagrams

Assume that before each example below we execute: s = [2, 3] t = [5, 6]

18

Operation Example Result append adds one element to a list s.append(t) t = 0 s → [2, 3, [5, 6]] t → 0 extend adds all elements in one list to another list s.extend(t) t[1] = 0 s → [2, 3, 5, 6] t → [5, 0] addition & slicing create new lists containing existing elements a = s + [t] b = a[1:] a[1] = 9 b[1][1] = 0

Global b s list 1

2

t

3

list 1

5 6

list 1

2 3

2 a

Lists in Environment Diagrams

Assume that before each example below we execute: s = [2, 3] t = [5, 6]

18

Operation Example Result append adds one element to a list s.append(t) t = 0 s → [2, 3, [5, 6]] t → 0 extend adds all elements in one list to another list s.extend(t) t[1] = 0 s → [2, 3, 5, 6] t → [5, 0] addition & slicing create new lists containing existing elements a = s + [t] b = a[1:] a[1] = 9 b[1][1] = 0

Global b s list 1

2

t

3

list 1

5 6

list 1

2 3

2 a list 1

3

Lists in Environment Diagrams

Assume that before each example below we execute: s = [2, 3] t = [5, 6]

18

Operation Example Result append adds one element to a list s.append(t) t = 0 s → [2, 3, [5, 6]] t → 0 extend adds all elements in one list to another list s.extend(t) t[1] = 0 s → [2, 3, 5, 6] t → [5, 0] addition & slicing create new lists containing existing elements a = s + [t] b = a[1:] a[1] = 9 b[1][1] = 0

Global b s list 1

2

t

3

list 1

5 6

list 1

2 3

2 a list 1

3 9

Lists in Environment Diagrams

Assume that before each example below we execute: s = [2, 3] t = [5, 6]

18

Operation Example Result append adds one element to a list s.append(t) t = 0 s → [2, 3, [5, 6]] t → 0 extend adds all elements in one list to another list s.extend(t) t[1] = 0 s → [2, 3, 5, 6] t → [5, 0] addition & slicing create new lists containing existing elements a = s + [t] b = a[1:] a[1] = 9 b[1][1] = 0

Global b s list 1

2

t

3

list 1

5 6

list 1

2 3

2 a list 1

3 9

Lists in Environment Diagrams

Assume that before each example below we execute: s = [2, 3] t = [5, 6]

18

Operation Example Result append adds one element to a list s.append(t) t = 0 s → [2, 3, [5, 6]] t → 0 extend adds all elements in one list to another list s.extend(t) t[1] = 0 s → [2, 3, 5, 6] t → [5, 0] addition & slicing create new lists containing existing elements a = s + [t] b = a[1:] a[1] = 9 b[1][1] = 0 s → [2, 3] t → [5, 0] a → [2, 9, [5, 0]] b → [3, [5, 0]]

Global b s list 1

2

t

3

list 1

5 6

list 1

2 3

2 a list 1

3 9

Lists in Environment Diagrams

Assume that before each example below we execute: s = [2, 3] t = [5, 6]

19

Global s list 1

2

t

3

list 1

5 6

Operation Example Result append adds one element to a list s.append(t) t = 0 s → [2, 3, [5, 6]] t → 0 extend adds all elements in one list to another list s.extend(t) t[1] = 0 s → [2, 3, 5, 6] t → [5, 0] addition & slicing create new lists containing existing elements a = s + [t] b = a[1:] a[1] = 9 b[1][1] = 0 s → [2, 3] t → [5, 0] a → [2, 9, [5, 0]] b → [3, [5, 0]] The list function also creates a new list containing existing elements t = list(s) s[1] = 0

Lists in Environment Diagrams

Assume that before each example below we execute: s = [2, 3] t = [5, 6]

19

Global s list 1

2

t

3

list 1

5 6

Operation Example Result append adds one element to a list s.append(t) t = 0 s → [2, 3, [5, 6]] t → 0 extend adds all elements in one list to another list s.extend(t) t[1] = 0 s → [2, 3, 5, 6] t → [5, 0] addition & slicing create new lists containing existing elements a = s + [t] b = a[1:] a[1] = 9 b[1][1] = 0 s → [2, 3] t → [5, 0] a → [2, 9, [5, 0]] b → [3, [5, 0]] The list function also creates a new list containing existing elements t = list(s) s[1] = 0

list 1

2 3

Lists in Environment Diagrams

Assume that before each example below we execute: s = [2, 3] t = [5, 6]

19

Global s list 1

2

t

3

list 1

5 6

Operation Example Result append adds one element to a list s.append(t) t = 0 s → [2, 3, [5, 6]] t → 0 extend adds all elements in one list to another list s.extend(t) t[1] = 0 s → [2, 3, 5, 6] t → [5, 0] addition & slicing create new lists containing existing elements a = s + [t] b = a[1:] a[1] = 9 b[1][1] = 0 s → [2, 3] t → [5, 0] a → [2, 9, [5, 0]] b → [3, [5, 0]] The list function also creates a new list containing existing elements t = list(s) s[1] = 0

list 1

2 3

Lists in Environment Diagrams

Assume that before each example below we execute: s = [2, 3] t = [5, 6]

19

Global s list 1

2

t

3

list 1

5 6

Operation Example Result append adds one element to a list s.append(t) t = 0 s → [2, 3, [5, 6]] t → 0 extend adds all elements in one list to another list s.extend(t) t[1] = 0 s → [2, 3, 5, 6] t → [5, 0] addition & slicing create new lists containing existing elements a = s + [t] b = a[1:] a[1] = 9 b[1][1] = 0 s → [2, 3] t → [5, 0] a → [2, 9, [5, 0]] b → [3, [5, 0]] The list function also creates a new list containing existing elements t = list(s) s[1] = 0

list 1

2 3

Lists in Environment Diagrams

Assume that before each example below we execute: s = [2, 3] t = [5, 6]

19

Global s list 1

2

t

3

list 1

5 6

Operation Example Result append adds one element to a list s.append(t) t = 0 s → [2, 3, [5, 6]] t → 0 extend adds all elements in one list to another list s.extend(t) t[1] = 0 s → [2, 3, 5, 6] t → [5, 0] addition & slicing create new lists containing existing elements a = s + [t] b = a[1:] a[1] = 9 b[1][1] = 0 s → [2, 3] t → [5, 0] a → [2, 9, [5, 0]] b → [3, [5, 0]] The list function also creates a new list containing existing elements t = list(s) s[1] = 0

list 1

2 3

s → [2, 0] t → [2, 3]

Lists in Environment Diagrams

Assume that before each example below we execute: s = [2, 3] t = [5, 6]

20

Global s list 1

2

t

3

list 1

5 6

Operation Example Result append adds one element to a list s.append(t) t = 0 s → [2, 3, [5, 6]] t → 0 extend adds all elements in one list to another list s.extend(t) t[1] = 0 s → [2, 3, 5, 6] t → [5, 0] addition & slicing create new lists containing existing elements a = s + [t] b = a[1:] a[1] = 9 b[1][1] = 0 s → [2, 3] t → [5, 0] a → [2, 9, [5, 0]] b → [3, [5, 0]] The list function also creates a new list containing existing elements t = list(s) s[1] = 0 s → [2, 0] t → [2, 3] slice assignment replaces a slice with new values s[0:0] = t s[3:] = t t[1] = 0

Lists in Environment Diagrams

Assume that before each example below we execute: s = [2, 3] t = [5, 6]

21

Global s list 1

5

t

6

list 1

5 6

Operation Example Result append adds one element to a list s.append(t) t = 0 s → [2, 3, [5, 6]] t → 0 extend adds all elements in one list to another list s.extend(t) t[1] = 0 s → [2, 3, 5, 6] t → [5, 0] addition & slicing create new lists containing existing elements a = s + [t] b = a[1:] a[1] = 9 b[1][1] = 0 s → [2, 3] t → [5, 0] a → [2, 9, [5, 0]] b → [3, [5, 0]] The list function also creates a new list containing existing elements t = list(s) s[1] = 0 s → [2, 0] t → [2, 3] slice assignment replaces a slice with new values s[0:0] = t s[3:] = t t[1] = 0

3 2

2 3

Lists in Environment Diagrams

Assume that before each example below we execute: s = [2, 3] t = [5, 6]

21

Global s list 1

5

t

6

list 1

5 6

Operation Example Result append adds one element to a list s.append(t) t = 0 s → [2, 3, [5, 6]] t → 0 extend adds all elements in one list to another list s.extend(t) t[1] = 0 s → [2, 3, 5, 6] t → [5, 0] addition & slicing create new lists containing existing elements a = s + [t] b = a[1:] a[1] = 9 b[1][1] = 0 s → [2, 3] t → [5, 0] a → [2, 9, [5, 0]] b → [3, [5, 0]] The list function also creates a new list containing existing elements t = list(s) s[1] = 0 s → [2, 0] t → [2, 3] slice assignment replaces a slice with new values s[0:0] = t s[3:] = t t[1] = 0

3 2

2 3 5

4

6

Lists in Environment Diagrams

Assume that before each example below we execute: s = [2, 3] t = [5, 6]

21

Global s list 1

5

t

6

list 1

5 6

Operation Example Result append adds one element to a list s.append(t) t = 0 s → [2, 3, [5, 6]] t → 0 extend adds all elements in one list to another list s.extend(t) t[1] = 0 s → [2, 3, 5, 6] t → [5, 0] addition & slicing create new lists containing existing elements a = s + [t] b = a[1:] a[1] = 9 b[1][1] = 0 s → [2, 3] t → [5, 0] a → [2, 9, [5, 0]] b → [3, [5, 0]] The list function also creates a new list containing existing elements t = list(s) s[1] = 0 s → [2, 0] t → [2, 3] slice assignment replaces a slice with new values s[0:0] = t s[3:] = t t[1] = 0

3 2

2 3 5

4

6

Lists in Environment Diagrams

Assume that before each example below we execute: s = [2, 3] t = [5, 6]

21

Global s list 1

5

t

6

list 1

5 6

Operation Example Result append adds one element to a list s.append(t) t = 0 s → [2, 3, [5, 6]] t → 0 extend adds all elements in one list to another list s.extend(t) t[1] = 0 s → [2, 3, 5, 6] t → [5, 0] addition & slicing create new lists containing existing elements a = s + [t] b = a[1:] a[1] = 9 b[1][1] = 0 s → [2, 3] t → [5, 0] a → [2, 9, [5, 0]] b → [3, [5, 0]] The list function also creates a new list containing existing elements t = list(s) s[1] = 0 s → [2, 0] t → [2, 3] slice assignment replaces a slice with new values s[0:0] = t s[3:] = t t[1] = 0

3 2

2 3 5

4

6

s → [5, 6, 2, 5, 6] t → [5, 0]

Lists in Environment Diagrams

Assume that before each example below we execute: s = [2, 3] t = [5, 6]

22

Lists in Environment Diagrams

Assume that before each example below we execute: s = [2, 3] t = [5, 6]

22

Operation Example Result

Lists in Environment Diagrams

Assume that before each example below we execute: s = [2, 3] t = [5, 6]

22

Operation Example Result pop removes & returns the last element

Lists in Environment Diagrams

Assume that before each example below we execute: s = [2, 3] t = [5, 6]

22

Operation Example Result pop removes & returns the last element removes & returns t = s.pop()

Lists in Environment Diagrams

Assume that before each example below we execute: s = [2, 3] t = [5, 6]

22

Operation Example Result pop removes & returns the last element removes & returns t = s.pop() s → [2] t → 3

Lists in Environment Diagrams

Assume that before each example below we execute: s = [2, 3] t = [5, 6]

22

Operation Example Result pop removes & returns the last element removes & returns t = s.pop() s → [2] t → 3 remove removes the first element equal to the argument

Lists in Environment Diagrams

Assume that before each example below we execute: s = [2, 3] t = [5, 6]

22

Operation Example Result pop removes & returns the last element removes & returns t = s.pop() s → [2] t → 3 remove removes the first element equal to the argument t.extend(t) t.remove(5)

Lists in Environment Diagrams

Assume that before each example below we execute: s = [2, 3] t = [5, 6]

22

Operation Example Result pop removes & returns the last element removes & returns t = s.pop() s → [2] t → 3 remove removes the first element equal to the argument t.extend(t) t.remove(5) s → [2, 3] t → [6, 5, 6]

Lists in Environment Diagrams

Assume that before each example below we execute: s = [2, 3] t = [5, 6]

22

Operation Example Result pop removes & returns the last element removes & returns t = s.pop() s → [2] t → 3 remove removes the first element equal to the argument t.extend(t) t.remove(5) s → [2, 3] t → [6, 5, 6] slice assignment can remove elements from a list by assigning [] to a slice.

Lists in Environment Diagrams

Assume that before each example below we execute: s = [2, 3] t = [5, 6]

22

Operation Example Result pop removes & returns the last element removes & returns t = s.pop() s → [2] t → 3 remove removes the first element equal to the argument t.extend(t) t.remove(5) s → [2, 3] t → [6, 5, 6] slice assignment can remove elements from a list by assigning [] to a slice. s[:1] = [] t[0:2] = []

Lists in Environment Diagrams

Assume that before each example below we execute: s = [2, 3] t = [5, 6]

22

Operation Example Result pop removes & returns the last element removes & returns t = s.pop() s → [2] t → 3 remove removes the first element equal to the argument t.extend(t) t.remove(5) s → [2, 3] t → [6, 5, 6] slice assignment can remove elements from a list by assigning [] to a slice. s[:1] = [] t[0:2] = [] s → [3] t → []

Lists in Lists in Lists in Environment Diagrams

t = [1, 2, 3] t[1:3] = [t] t.extend(t)

23

t = [[1, 2], [3, 4]] t[0].append(t[1:2])

Lists in Lists in Lists in Environment Diagrams

t = [1, 2, 3] t[1:3] = [t] t.extend(t)

23

t = [[1, 2], [3, 4]] t[0].append(t[1:2])

Global t list 1

1 2

2

3

Lists in Lists in Lists in Environment Diagrams

t = [1, 2, 3] t[1:3] = [t] t.extend(t)

23

t = [[1, 2], [3, 4]] t[0].append(t[1:2])

Global t list 1

1 2

2

3

list [t] evaluates to:

Lists in Lists in Lists in Environment Diagrams

t = [1, 2, 3] t[1:3] = [t] t.extend(t)

23

t = [[1, 2], [3, 4]] t[0].append(t[1:2])

Global t list 1

1 2

2

3

list [t] evaluates to:

Lists in Lists in Lists in Environment Diagrams

t = [1, 2, 3] t[1:3] = [t] t.extend(t)

23

t = [[1, 2], [3, 4]] t[0].append(t[1:2])

Global t list 1

1 2

2

3

list [t] evaluates to: 1

Lists in Lists in Lists in Environment Diagrams

t = [1, 2, 3] t[1:3] = [t] t.extend(t)

23

t = [[1, 2], [3, 4]] t[0].append(t[1:2])

Global t list 1

1 2

2

3

1

Lists in Lists in Lists in Environment Diagrams

t = [1, 2, 3] t[1:3] = [t] t.extend(t)

23

t = [[1, 2], [3, 4]] t[0].append(t[1:2])

Global t list 1

1 2

2

3

1 2

1

3

Lists in Lists in Lists in Environment Diagrams

t = [1, 2, 3] t[1:3] = [t] t.extend(t)

23

t = [[1, 2], [3, 4]] t[0].append(t[1:2])

Global t list 1

1 2

2

3

1 2

1

3

[1, [...], 1, [...]]

Lists in Lists in Lists in Environment Diagrams

t = [1, 2, 3] t[1:3] = [t] t.extend(t)

23

t = [[1, 2], [3, 4]] t[0].append(t[1:2])

Global t list 1

1 2

2

3

1 2

1

3 Global t list 1 list 1

1 2

list 1

3 4

[1, [...], 1, [...]]

Lists in Lists in Lists in Environment Diagrams

t = [1, 2, 3] t[1:3] = [t] t.extend(t)

23

t = [[1, 2], [3, 4]] t[0].append(t[1:2])

Global t list 1

1 2

2

3

1 2

1

3 Global t list 1 list 1

1 2

list 1

3 4

list

[1, [...], 1, [...]]

Lists in Lists in Lists in Environment Diagrams

t = [1, 2, 3] t[1:3] = [t] t.extend(t)

23

t = [[1, 2], [3, 4]] t[0].append(t[1:2])

Global t list 1

1 2

2

3

1 2

1

3 Global t list 1 list 1

1 2

list 1

3 4

list 2

[1, [...], 1, [...]]

Lists in Lists in Lists in Environment Diagrams

t = [1, 2, 3] t[1:3] = [t] t.extend(t)

23

t = [[1, 2], [3, 4]] t[0].append(t[1:2])

Global t list 1

1 2

2

3

1 2

1

3 Global t list 1 list 1

1 2

list 1

3 4

list 2

[1, [...], 1, [...]] [[1, 2, [[3, 4]]], [3, 4]]