Nested Data Structures - Stanford University...Nesting data structures can help us store even more...
Transcript of Nested Data Structures - Stanford University...Nesting data structures can help us store even more...
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Nested Data StructuresCS106AP Lecture 15
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RoadmapProgramming Basics
The Console Images
Data structures
MidtermGraphics
Object-Oriented Programming
Everyday Python
Life after CS106AP!
Day 1!
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Images
The Console
Everyday PythonObject-Oriented Programming
MidtermGraphics
Programming Basics
Roadmap
Life after CS106AP!
Day 1!
Data structures
ListsFilesParsing: Strings
Dictionaries 1.0
Dictionaries 2.0
Nested Data Structures
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Today’s questions
How can we store more information and add more structure to our data?
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Today’s topics
1. Review
2. Built-ins
3. Nested data structures
Lists
Dictionaries
4. What’s next?
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Review
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Big Picture: Dictionaries + Uniqueness
● A key will only be associated with one value
○ no duplicate keys!
● A dictionary can have multiple values that are the same.
dict
‘hansa’‘kandula’‘lumpy’‘surus’
3313
keys values
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Accessing a Dictionary’s Keys
>>> d = {‘Gates’: 23, ‘MemChu’: 116, ‘Tresidder’: 57}
>>> d.keys()
dict_keys(['Gates', 'MemChu', 'Tresidder'])
iterable collection of all the keys.iterable means it can be used in foreach
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Accessing a Dictionary’s Keys
>>> d = {‘Gates’: 23, ‘MemChu’: 116, ‘Tresidder’: 57}
>>> list(d.keys())
[‘Gates’, ‘MemChu’, ‘Tresidder’]
we are using list() to convert d.keys() into a list
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Accessing a Dictionary’s Values
>>> d = {‘Gates’: 23, ‘MemChu’: 116, ‘Tresidder’: 57}
>>> list(d.values())
[23, 116, 57]
we are using list() to convert d.values() into a list
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Looping over a Dictionary’s Keys
>>> d = {‘Gates’: 23, ‘MemChu’: 116, ‘Tresidder’: 57}
>>> for building in d.keys():
... print(building)
Gates
MemChu
Tresidder
we can use foreach on the dictionary’s keys!
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Looping over a Dictionary’s Values
>>> d = {‘Gates’: 23, ‘MemChu’: 116, ‘Tresidder’: 57}
>>> for age in d.values():
... print(age)
23
116
57
we can use foreach on the dictionary’s values!
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Looping over a Dictionary’s Keys and Values
>>> d = {‘Gates’: 23, ‘MemChu’: 116, ‘Tresidder’: 57}
>>> for building, age in d.items():
... print(building, ‘is’, age, ‘years old.’)
Gates is 23 years old.
MemChu is 116 years old.
Tresidder is 57 years old.
items() gives us key, value pairs
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Printing with sep=
>>> d = {‘Gates’: 23, ‘MemChu’: 116, ‘Tresidder’: 57}
>>> for building, age in d.items():
... print(building, age, sep=‘: ’)
Gates: 23
MemChu: 116
Tresidder: 57
sep is an optional argument like end!
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Printing with sep=
>>> d = {‘Gates’: 23, ‘MemChu’: 116, ‘Tresidder’: 57}
>>> for building, age in d.items():
... print(building, age, sep=‘: ’)
Gates: 23
MemChu: 116
Tresidder: 57
the separating string will be printed between the arguments you pass into print()
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Getting a Sorted List of Keys
>>> d = {‘Gates’: 23, ‘Tresidder’: 57, ‘MemChu’: 116}
>>> sorted(d.keys())
['Gates', 'MemChu', 'Tresidder']
sorted() returns a list in alphabetical order!
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Retrieving Min/Max Values
>>> d = {‘Gates’: 23, ‘MemChu’: 116, ‘Tresidder’: 57}
>>> min(d.values())
23
>>> max(d.values())
116
returns the smallest element!
returns the biggest element!
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Built-in FunctionA function built into Python that is always
available for use.
Definition
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Examples of Built-ins
print()input()str()int()float()len()
open()list()sorted()max()min()
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Built-ins with Lists
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Sorted() in Lists
>>> lst = [10, -2, 34, 46, 5]
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Sorted() in Lists
>>> lst = [10, -2, 34, 46, 5]>>> sorted(lst)
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Sorted() in Lists
>>> lst = [10, -2, 34, 46, 5]>>> sorted(lst)
Creates an increasing sorted list
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Sorted() in Lists
>>> lst = [10, -2, 34, 46, 5]>>> sorted(lst)[-2, 5, 10, 34, 46]
Creates an increasing sorted list
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Sorted() in Lists
>>> lst = [10, -2, 34, 46, 5]>>> sorted(lst)[-2, 5, 10, 34, 46]>>> lst Creates an increasing sorted list
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Sorted() in Lists
>>> lst = [10, -2, 34, 46, 5]>>> sorted(lst)[-2, 5, 10, 34, 46]>>> lst[10, -2, 34, 46, 5]
Creates an increasing sorted list
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Sorted() in Lists
>>> lst = [10, -2, 34, 46, 5]
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Sorted() in Lists
>>> lst = [10, -2, 34, 46, 5]>>> sorted(lst, reverse=True)
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Sorted() in Lists
>>> lst = [10, -2, 34, 46, 5]>>> sorted(lst, reverse=True)[46, 34, 10, 5, -2]
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Sorted() in Lists
>>> lst = [10, -2, 34, 46, 5]>>> sorted(lst, reverse=True)[46, 34, 10, 5, -2]
You can pass in an optional parameter, reverse=True.
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Max/Min in Lists
>>> lst = [10, -2, 34, 46, 5]
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Max/Min in Lists
>>> lst = [10, -2, 34, 46, 5]>>> max(lst)
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Max/Min in Lists
>>> lst = [10, -2, 34, 46, 5]>>> max(lst)
Returns the maximum element in the list
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Max/Min in Lists
>>> lst = [10, -2, 34, 46, 5]>>> max(lst)46
Returns the maximum element in the list
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Max/Min in Lists
>>> lst = [10, -2, 34, 46, 5]>>> max(lst)46>>> min(lst)
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Max/Min in Lists
>>> lst = [10, -2, 34, 46, 5]>>> max(lst)46>>> min(lst)
Returns the minimum element in the list
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Max/Min in Lists
>>> lst = [10, -2, 34, 46, 5]>>> max(lst)46>>> min(lst)-2
Returns the minimum element in the list
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Max/Min in Lists
>>> lst = [‘a’, ‘b’, ‘c’, ‘d’]
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Max/Min in Lists
>>> lst = [‘a’, ‘b’, ‘c’, ‘d’]>>> max(lst)
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Max/Min in Lists
>>> lst = [‘a’, ‘b’, ‘c’, ‘d’]>>> max(lst)
We can use max/min on strings because characters have unicode representations
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Max/Min in Lists
>>> lst = [‘a’, ‘b’, ‘c’, ‘d’]>>> max(lst)‘d’
We can use max/min on strings because characters have unicode representations
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Max/Min in Lists
>>> lst = [‘a’, ‘b’, ‘c’, ‘d’]>>> max(lst)‘d’
We can use max/min on strings because characters have unicode representations
‘\u0064’, or 100 in decimal
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Max/Min in Lists
>>> lst = [‘a’, ‘b’, ‘c’, ‘d’]>>> max(lst)‘d’>>> min(lst) We can use max/min on strings because
characters have unicode representations
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Max/Min in Lists
>>> lst = [‘a’, ‘b’, ‘c’, ‘d’]>>> max(lst)‘d’>>> min(lst)‘a’
We can use max/min on strings because characters have unicode representations
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Max/Min in Lists
>>> lst = [‘a’, ‘b’, ‘c’, ‘d’]>>> max(lst)‘d’>>> min(lst)‘a’
We can use max/min on strings because characters have unicode representations
‘\u0061’, or 97 in decimal
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Max/Min in Lists
>>> lst = [‘a’, ‘b’, ‘c’, ‘d’]>>> max(lst)‘d’>>> min(lst)‘a’
We can use max/min on anything where “<” has meaning.
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Extending a List
>>> lst = [‘a’, ‘b’, ‘c’, ‘d’]
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Extending a List
>>> lst = [‘a’, ‘b’, ‘c’, ‘d’]>>> lst.extend([‘e’, ‘f’])
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Extending a List
>>> lst = [‘a’, ‘b’, ‘c’, ‘d’]>>> lst.extend([‘e’, ‘f’])>>> lst
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Extending a List
>>> lst = [‘a’, ‘b’, ‘c’, ‘d’]>>> lst.extend([‘e’, ‘f’])>>> lst[‘a’, ‘b’, ‘c’, ‘d’, ‘e’, ‘f’]
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Extending a List
>>> lst = [‘a’, ‘b’, ‘c’, ‘d’]>>> lst.extend([‘e’, ‘f’])>>> lst[‘a’, ‘b’, ‘c’, ‘d’, ‘e’, ‘f’] extend() behaves like +=
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Extending a List
>>> lst = [‘a’, ‘b’, ‘c’, ‘d’]>>> lst.extend([‘e’, ‘f’])>>> lst[‘a’, ‘b’, ‘c’, ‘d’, ‘e’, ‘f’]>>> lst += [‘g’, ‘h’]
extend() behaves like +=
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Extending a List
>>> lst = [‘a’, ‘b’, ‘c’, ‘d’]>>> lst.extend([‘e’, ‘f’])>>> lst[‘a’, ‘b’, ‘c’, ‘d’, ‘e’, ‘f’]>>> lst += [‘g’, ‘h’]>>> lst
extend() behaves like +=
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Extending a List
>>> lst = [‘a’, ‘b’, ‘c’, ‘d’]>>> lst.extend([‘e’, ‘f’])>>> lst[‘a’, ‘b’, ‘c’, ‘d’, ‘e’, ‘f’]>>> lst += [‘g’, ‘h’]>>> lst[‘a’, ‘b’, ‘c’, ‘d’, ‘e’, ‘f’, ‘g’, ‘h’]
extend() behaves like +=
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Note on Efficiency
>>> lst = [‘a’, ‘b’, ‘c’, ‘d’]>>> lst += [‘e’, ‘f’]
>>> lst = lst + [‘e’, ‘f’]
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Note on Efficiency
>>> lst = [‘a’, ‘b’, ‘c’, ‘d’]>>> lst += [‘e’, ‘f’]
>>> lst = lst + [‘e’, ‘f’]
This creates a new list every time, so when the list gets long, it’s inefficient.
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Note on Efficiency
>>> lst = [‘a’, ‘b’, ‘c’, ‘d’]>>> lst += [‘e’, ‘f’]
>>> lst = lst + [‘e’, ‘f’]
This creates a new list every time, so when the list gets long, it’s inefficient.
This modifies in-place, so it’s fast!
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How can we store more information by adding more
structure to our data?
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Recall: Animal – Feedings Dictionary
dict
‘hansa’‘kandula’‘lumpy’‘surus’
3214
keys values● animal name ⟶
number of feedings
● string ⟶ int
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Recall: Animal – Feedings Dictionary
dict
‘hansa’‘kandula’‘lumpy’‘surus’
3214
keys values● animal name ⟶
number of feedings
● string ⟶ int
What if we wanted to store the times that the animals were fed?
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Attempt #1: Animal – Feeding Times Dictionary
● animal name ⟶ feeding times
● string ⟶ string
What if we wanted to store the times that the animals were fed?
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Attempt #1: Animal – Feeding Times Dictionary
dict
‘hansa’‘kandula’‘lumpy’‘surus’
‘12:00,3:00,9:00’
‘8:00,1:00’
‘11:00’
‘5:00,3:00,9:00,2:00’
keys values● animal name ⟶
feeding times
● string ⟶ string
What if we wanted to store the times that the animals were fed?
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Attempt #1: Animal – Feeding Times Dictionary
dict
‘hansa’‘kandula’‘lumpy’‘surus’
‘12:00,3:00,9:00’
‘8:00,1:00’
‘11:00’
‘5:00,3:00,9:00,2:00’
keys values● animal name ⟶
feeding times
● string ⟶ string
What if we wanted to store the times that the animals were fed? Times are not easily accessible!
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Attempt #1: Animal – Feeding Times Dictionary
dict
‘hansa’‘kandula’‘lumpy’‘surus’
‘12:00,3:00,9:00’
‘8:00,1:00’
‘11:00’
‘5:00,3:00,9:00,2:00’
keys values● animal name ⟶
feeding times
● string ⟶ string
What if we wanted to store the times that the animals were fed? We’d have to call s.split(‘,’) anytime
we wanted to access a time!
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Attempt #1: Animal – Feeding Times Dictionary
dict
‘hansa’‘kandula’‘lumpy’‘surus’
‘12:00,3:00,9:00’
‘8:00,1:00’
‘11:00’
‘5:00,3:00,9:00,2:00’
keys values● animal name ⟶
feeding times
● string ⟶ string
What if we wanted to store the times that the animals were fed? But those times look like a data type
we know of......
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Attempt #2: Animal – Feeding Times Dictionary
● animal name ⟶ feeding times
● string ⟶ list[string]
What if we wanted to store the times that the animals were fed?
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Attempt #2: Animal – Feeding Times Dictionary
dict
‘hansa’‘kandula’‘lumpy’‘surus’
[‘12:00’,‘3:00’,‘9:00’]
[‘8:00’,‘1:00’]
[‘11:00’]
[‘5:00’,‘3:00’,‘9:00’,‘2:00’]
keys values● animal name ⟶
feeding times
● string ⟶ list[string]
What if we wanted to store the times that the animals were fed?
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Attempt #2: Animal – Feeding Times Dictionary
dict
‘hansa’‘kandula’‘lumpy’‘surus’
[‘12:00’,‘3:00’,‘9:00’]
[‘8:00’,‘1:00’]
[‘11:00’]
[‘5:00’,‘3:00’,‘9:00’,‘2:00’]
keys values● animal name ⟶
feeding times
● string ⟶ list[string]
What if we wanted to store the times that the animals were fed? We can easily access the individual
times!
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Nested Data Structures
● We can nest data structures!
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Nested Data Structures
● We can nest data structures!
○ Lists in lists
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Nested Data Structures
● We can nest data structures!
○ Lists in lists
■ grid/game board
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Nested Data Structures
● We can nest data structures!
○ Lists in lists
■ grid/game board
○ Lists in dicts
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Nested Data Structures
● We can nest data structures!
○ Lists in lists
■ grid/game board
○ Lists in dicts
■ animals to feeding times
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Nested Data Structures
● We can nest data structures!
○ Lists in lists
■ grid/game board
○ Lists in dicts — (assignment 4)
■ animals to feeding times
○ Dicts in dicts
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Nested Data Structures
● We can nest data structures!
○ Lists in lists
■ grid/game board
○ Lists in dicts
■ animals to feeding times
○ Dicts in dicts
■ your phone’s contact book
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Nested Data Structures
● We can nest data structures!
○ Lists in lists
■ grid/game board
○ Lists in dicts
■ animals to feeding times
○ Dicts in dicts
■ your phone’s contact book
○ ... and so on!
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Attempt #2: Animal – Feeding Times Dictionary
dict
‘hansa’‘kandula’‘lumpy’‘surus’
[‘12:00’,‘3:00’,‘9:00’]
[‘8:00’,‘1:00’]
[‘11:00’]
[‘5:00’,‘3:00’,‘9:00’,‘2:00’]
keys values● animal name ⟶
number of feedings
● string ⟶ list[string]
What if we wanted to store the times that the animals were fed? How do we use this dictionary?
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Using a Dictionary Containing a List - Get
dict
‘hansa’‘kandula’‘lumpy’‘surus’
[‘12:00’,‘3:00’,‘9:00’]
[‘8:00’,‘1:00’]
[‘11:00’]
[‘5:00’,‘3:00’,‘9:00’,‘2:00’]
keys values
Get the feeding times associated with ‘hansa’!
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Using a Dictionary Containing a List - Get
Get the feeding times associated with ‘hansa’!
>>> d[‘hansa’] dict
‘hansa’‘kandula’‘lumpy’‘surus’
[‘12:00’,‘3:00’,‘9:00’]
[‘8:00’,‘1:00’]
[‘11:00’]
[‘5:00’,‘3:00’,‘9:00’,‘2:00’]
keys values
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Using a Dictionary Containing a List - Get
Get the feeding times associated with ‘hansa’!
>>> d[‘hansa’]
[‘12:00’,‘3:00’,‘9:00’]
dict
‘hansa’‘kandula’‘lumpy’‘surus’
[‘12:00’,‘3:00’,‘9:00’]
[‘8:00’,‘1:00’]
[‘11:00’]
[‘5:00’,‘3:00’,‘9:00’,‘2:00’]
keys values
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Using a Dictionary Containing a List - Modify Value
Add a feeding time (‘4:00’) to ‘lumpy’!
>>> d[‘hansa’]
[‘12:00’,‘3:00’,‘9:00’]
dict
‘hansa’‘kandula’‘lumpy’‘surus’
[‘12:00’,‘3:00’,‘9:00’]
[‘8:00’,‘1:00’]
[‘11:00’]
[‘5:00’,‘3:00’,‘9:00’,‘2:00’]
keys values
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Using a Dictionary Containing a List - Modify Value
Add a feeding time (‘4:00’) to ‘lumpy’!
>>> d[‘hansa’]
[‘12:00’,‘3:00’,‘9:00’]
>>> d[‘lumpy’].append(‘4:00’)
dict
‘hansa’‘kandula’‘lumpy’‘surus’
[‘12:00’,‘3:00’,‘9:00’]
[‘8:00’,‘1:00’]
[‘11:00’]
[‘5:00’,‘3:00’,‘9:00’,‘2:00’]
keys values
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Using a Dictionary Containing a List - Modify Value
Add a feeding time (‘4:00’) to ‘lumpy’!
>>> d[‘hansa’]
[‘12:00’,‘3:00’,‘9:00’]
>>> d[‘lumpy’].append(‘4:00’)
dict
‘hansa’‘kandula’‘lumpy’‘surus’
[‘12:00’,‘3:00’,‘9:00’]
[‘8:00’,‘1:00’]
[‘11:00’, ‘4:00’]
[‘5:00’,‘3:00’,‘9:00’,‘2:00’]
keys values
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Using a Dictionary Containing a List - Get Elem
Get the first feeding time for ‘kandula’
>>> d[‘hansa’]
[‘12:00’,‘3:00’,‘9:00’]
>>> d[‘lumpy’].append(‘4:00’)
dict
‘hansa’‘kandula’‘lumpy’‘surus’
[‘12:00’,‘3:00’,‘9:00’]
[‘8:00’,‘1:00’]
[‘11:00’, ‘4:00’]
[‘5:00’,‘3:00’,‘9:00’,‘2:00’]
keys values
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Using a Dictionary Containing a List - Get Elem
Get the first feeding time for ‘kandula’
>>> d[‘hansa’]
[‘12:00’,‘3:00’,‘9:00’]
>>> d[‘lumpy’].append(‘4:00’)
>>> k_times = d[‘kandula’]
dict
‘hansa’‘kandula’‘lumpy’‘surus’
[‘12:00’,‘3:00’,‘9:00’]
[‘8:00’,‘1:00’]
[‘11:00’, ‘4:00’]
[‘5:00’,‘3:00’,‘9:00’,‘2:00’]
keys values
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Using a Dictionary Containing a List - Get Elem
Get the first feeding time for ‘kandula’
>>> d[‘hansa’]
[‘12:00’,‘3:00’,‘9:00’]
>>> d[‘lumpy’].append(‘4:00’)
>>> k_times = d[‘kandula’]
[‘8:00’,‘1:00’]
dict
‘hansa’‘kandula’‘lumpy’‘surus’
[‘12:00’,‘3:00’,‘9:00’]
[‘8:00’,‘1:00’]
[‘11:00’, ‘4:00’]
[‘5:00’,‘3:00’,‘9:00’,‘2:00’]
keys values
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Using a Dictionary Containing a List - Get Elem
Get the first feeding time for ‘kandula’
>>> d[‘hansa’]
[‘12:00’,‘3:00’,‘9:00’]
>>> d[‘lumpy’].append(‘4:00’)
>>> k_times = d[‘kandula’]
[‘8:00’,‘1:00’]
>>> k_times[0]
dict
‘hansa’‘kandula’‘lumpy’‘surus’
[‘12:00’,‘3:00’,‘9:00’]
[‘8:00’,‘1:00’]
[‘11:00’, ‘4:00’]
[‘5:00’,‘3:00’,‘9:00’,‘2:00’]
keys values
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Using a Dictionary Containing a List - Get Elem
Get the first feeding time for ‘kandula’
>>> d[‘hansa’]
[‘12:00’,‘3:00’,‘9:00’]
>>> d[‘lumpy’].append(‘4:00’)
>>> k_times = d[‘kandula’]
[‘8:00’,‘1:00’]
>>> k_times[0]
‘8:00’
dict
‘hansa’‘kandula’‘lumpy’‘surus’
[‘12:00’,‘3:00’,‘9:00’]
[‘8:00’,‘1:00’]
[‘11:00’, ‘4:00’]
[‘5:00’,‘3:00’,‘9:00’,‘2:00’]
keys values
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Using a Dictionary Containing a List - Get Elem
Get the first feeding time for ‘kandula’
>>> d[‘hansa’]
[‘12:00’,‘3:00’,‘9:00’]
>>> d[‘lumpy’].append(‘4:00’)
>>> k_times = d[‘kandula’]
[‘8:00’,‘1:00’]
>>> k_times[0]
‘8:00’
>>> d[‘kandula’][0]
dict
‘hansa’‘kandula’‘lumpy’‘surus’
[‘12:00’,‘3:00’,‘9:00’]
[‘8:00’,‘1:00’]
[‘11:00’, ‘4:00’]
[‘5:00’,‘3:00’,‘9:00’,‘2:00’]
keys values
More concisely,
![Page 90: Nested Data Structures - Stanford University...Nesting data structures can help us store even more information in a . Object-Oriented Programming Data structures Everyday Python Life](https://reader034.fdocuments.us/reader034/viewer/2022050101/5f40c350bd222948ad4d5ce6/html5/thumbnails/90.jpg)
Using a Dictionary Containing a List - Get Elem
Get the first feeding time for ‘kandula’
>>> d[‘hansa’]
[‘12:00’,‘3:00’,‘9:00’]
>>> d[‘lumpy’].append(‘4:00’)
>>> k_times = d[‘kandula’]
[‘8:00’,‘1:00’]
>>> k_times[0]
‘8:00’
>>> d[‘kandula’][0]
‘8:00’
dict
‘hansa’‘kandula’‘lumpy’‘surus’
[‘12:00’,‘3:00’,‘9:00’]
[‘8:00’,‘1:00’]
[‘11:00’, ‘4:00’]
[‘5:00’,‘3:00’,‘9:00’,‘2:00’]
keys values
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Using a Dictionary Containing a List - Get Elem
Get the first feeding time for ‘kandula’
>>> d[‘hansa’]
[‘12:00’,‘3:00’,‘9:00’]
>>> d[‘lumpy’].append(‘4:00’)
>>> k_times = d[‘kandula’]
[‘8:00’,‘1:00’]
>>> k_times[0]
‘8:00’
>>> d[‘kandula’][0]
‘8:00’
dict
‘hansa’‘kandula’‘lumpy’‘surus’
[‘12:00’,‘3:00’,‘9:00’]
[‘8:00’,‘1:00’]
[‘11:00’, ‘4:00’]
[‘5:00’,‘3:00’,‘9:00’,‘2:00’]
keys values
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Using a Dictionary Containing a List - Set List
Reset ‘surus’ feeding list to [ ‘7:00’]
dict
‘hansa’‘kandula’‘lumpy’‘surus’
[‘12:00’,‘3:00’,‘9:00’]
[‘8:00’,‘1:00’]
[‘11:00’, ‘4:00’]
[‘5:00’,‘3:00’,‘9:00’,‘2:00’]
keys values
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Using a Dictionary Containing a List - Set List
Reset ‘surus’ feeding list to [ ‘7:00’]
>>> d[‘surus’] = [‘7:00’] dict
‘hansa’‘kandula’‘lumpy’‘surus’
[‘12:00’,‘3:00’,‘9:00’]
[‘8:00’,‘1:00’]
[‘11:00’, ‘4:00’]
[‘5:00’,‘3:00’,‘9:00’,‘2:00’]
keys values
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Using a Dictionary Containing a List - Set List
Reset ‘surus’ feeding list to [ ‘7:00’]
>>> d[‘surus’] = [‘7:00’] dict
‘hansa’‘kandula’‘lumpy’‘surus’
[‘12:00’,‘3:00’,‘9:00’]
[‘8:00’,‘1:00’]
[‘11:00’, ‘4:00’]
[‘7:00’]
keys values
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Using a Dictionary Containing a List - Set Element
Set second element in ‘lumpy’ to ‘2:00’
>>> d[‘surus’] = [‘7:00’] dict
‘hansa’‘kandula’‘lumpy’‘surus’
[‘12:00’,‘3:00’,‘9:00’]
[‘8:00’,‘1:00’]
[‘11:00’, ‘4:00’]
[‘7:00’]
keys values
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Using a Dictionary Containing a List - Set Element
Set second element in ‘lumpy’ to ‘2:00’
>>> d[‘surus’] = [‘7:00’]
>>> lump_list = d[‘lumpy’]
dict
‘hansa’‘kandula’‘lumpy’‘surus’
[‘12:00’,‘3:00’,‘9:00’]
[‘8:00’,‘1:00’]
[‘11:00’, ‘4:00’]
[‘7:00’]
keys values
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Using a Dictionary Containing a List - Set Element
Set second element in ‘lumpy’ to ‘2:00’
>>> d[‘surus’] = [‘7:00’]
>>> lump_list = d[‘lumpy’]
>>> lump_list[1] = ‘2:00’
dict
‘hansa’‘kandula’‘lumpy’‘surus’
[‘12:00’,‘3:00’,‘9:00’]
[‘8:00’,‘1:00’]
[‘11:00’, ‘4:00’]
[‘7:00’]
keys values
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Using a Dictionary Containing a List - Set Element
Set second element in ‘lumpy’ to ‘2:00’
>>> d[‘surus’] = [‘7:00’]
>>> lump_list = d[‘lumpy’]
>>> lump_list[1] = ‘2:00’
dict
‘hansa’‘kandula’‘lumpy’‘surus’
[‘12:00’,‘3:00’,‘9:00’]
[‘8:00’,‘1:00’]
[‘11:00’, ‘2:00’]
[‘7:00’]
keys values
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Using a Dictionary Containing a List - Set Element
Set second element in ‘lumpy’ to ‘2:00’
>>> d[‘surus’] = [‘7:00’]
>>> lump_list = d[‘lumpy’]
>>> lump_list[1] = ‘2:00’
# This is the same thing as:
dict
‘hansa’‘kandula’‘lumpy’‘surus’
[‘12:00’,‘3:00’,‘9:00’]
[‘8:00’,‘1:00’]
[‘11:00’, ‘2:00’]
[‘7:00’]
keys values
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Using a Dictionary Containing a List - Set Element
Set second element in ‘lumpy’ to ‘2:00’
>>> d[‘surus’] = [‘7:00’]
>>> lump_list = d[‘lumpy’]
>>> lump_list[1] = ‘2:00’
# This is the same thing as:
>>> d[‘lumpy’][1] = ‘2:00’
dict
‘hansa’‘kandula’‘lumpy’‘surus’
[‘12:00’,‘3:00’,‘9:00’]
[‘8:00’,‘1:00’]
[‘11:00’, ‘2:00’]
[‘7:00’]
keys values
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Think/Pair/Share:How can we modify our file-reading function to populate the animal – feeding times dictionary?
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General Note on Mutability
● Lists and dicts are both mutable data types
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General Note on Mutability
● Lists and dicts are both mutable data types
○ We can append or set, and these will modify the original object
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General Note on Mutability
● Lists and dicts are both mutable data types
○ We can append or set, and these will modify the original object
○ If we pass a list or a dict into a function and modify it, our changes will persist.
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General Note on Mutability
● Lists and dicts are both mutable data types
○ We can append or set, and these will modify the original object
○ If we pass a list or a dict into a function and modify it, our changes will persist. [DEMO]
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General Note on Mutability
● Lists and dicts are both mutable data types
○ We can append or set, and these will modify the original object
○ If we pass a list or a dict into a function and modify it, our changes will persist.
● Only immutable types can be used as dictionary keys
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General Note on Mutability
● Lists and dicts are both mutable data types
○ We can append or set, and these will modify the original object
○ If we pass a list or a dict into a function and modify it, our changes will persist.
● Only immutable types can be used as dictionary keys
○ e.g. strings, ints, floats, booleans
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General Note on Mutability
● Lists and dicts are both mutable data types
○ We can append or set, and these will modify the original object
○ If we pass a list or a dict into a function and modify it, our changes will persist.
● Only immutable types can be used as dictionary keys
○ e.g. strings, ints, floats, booleans
○ immutable or mutable types can be dictionary values
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General Note on Mutability
● Lists and dicts are both mutable data types
○ We can append or set, and these will modify the original object
○ If we pass a list or a dict into a function and modify it, our changes will persist.
● Only immutable types can be used as dictionary keys
○ e.g. strings, ints, floats, booleans
○ immutable or mutable types can be dictionary values
■ e.g. strings, ints, floats, booleans, lists, dictionaries
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Think/Pair/Share:How could we store an animal’s type, diet, and feeding times in a data structure?
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Attempt #1: Animal – Info List Dictionary
● animal name ⟶ animal type, diet, feeding times
● string ⟶ list
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Attempt #1: Animal – Info List Dictionary
dict
‘hansa’‘kandula’‘lumpy’‘surus’
[‘elephant’, ‘grass’, ‘12:00’,‘3:00’,‘9:00’]
[‘elephant’, ‘grass’, ‘8:00’,‘1:00’]
[‘tortoise’, ‘kale’, ‘11:00’]
[‘elephant’, ‘roots’, ‘5:00’,‘3:00’,‘9:00’,‘2:00’]
keys values● animal name ⟶
animal type, diet, feeding times
● string ⟶ list
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Attempt #1: Animal – Info List Dictionary
dict
‘hansa’‘kandula’‘lumpy’‘surus’
[‘elephant’, ‘grass’, ‘12:00’,‘3:00’,‘9:00’]
[‘elephant’, ‘grass’, ‘8:00’,‘1:00’]
[‘tortoise’, ‘kale’, ‘11:00’]
[‘elephant’, ‘roots’, ‘5:00’,‘3:00’,‘9:00’,‘2:00’]
keys values● animal name ⟶
animal type, diet, feeding times
● string ⟶ list
Not super easy to distinguish between the different pieces of data in the list
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Dicts in Dicts!
dict
‘hansa’‘kandula’‘lumpy’‘surus’
keys values
Image from Allie Brosh
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Attempt #2: Animal – Info Dict Dictionary
● animal name ⟶ animal type, diet, feeding times
● string ⟶ dict
● use strings as keys to specify what field the values correspond to
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Attempt #2: Animal – Info Dict Dictionary
dict
‘hansa’
‘kandula’
‘lumpy’
‘surus’
keys values● animal name ⟶
animal type, diet, feeding times
● string ⟶ dict
● use strings as keys to specify what field the values correspond to
‘type’‘diet’‘times’
‘elephant’‘grass’
[‘12:00’,‘3:00’,‘9:00’]
‘type’‘diet’‘times’
‘elephant’‘grass’
[‘8:00’,‘1:00’]
‘type’‘diet’‘times’
‘tortoise’‘kale’
[‘11:00’]
‘type’‘diet’‘times’
‘elephant’‘roots’
[‘5:00’,‘3:00’,‘9:00’,‘2:00’]
![Page 117: Nested Data Structures - Stanford University...Nesting data structures can help us store even more information in a . Object-Oriented Programming Data structures Everyday Python Life](https://reader034.fdocuments.us/reader034/viewer/2022050101/5f40c350bd222948ad4d5ce6/html5/thumbnails/117.jpg)
Attempt #2: Animal – Info Dict Dictionary
dict
‘hansa’
‘kandula’
‘lumpy’
‘surus’
keys values● animal name ⟶
animal type, diet, feeding times
● string ⟶ dict
● use strings as keys to specify what field the values correspond to
‘type’‘diet’‘times’
‘elephant’‘grass’
[‘12:00’,‘3:00’,‘9:00’]
‘type’‘diet’‘times’
‘elephant’‘grass’
[‘8:00’,‘1:00’]
‘type’‘diet’‘times’
‘tortoise’‘kale’
[‘11:00’]
‘type’‘diet’‘times’
‘elephant’‘roots’
[‘5:00’,‘3:00’,‘9:00’,‘2:00’]
you can have values of different types
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Attempt #2: Animal – Info Dict Dictionary
dict
‘hansa’
‘kandula’
‘lumpy’
‘surus’
keys values● animal name ⟶
animal type, diet, feeding times
● string ⟶ dict
● use strings as keys to specify what field the values correspond to
‘type’‘diet’‘times’
‘elephant’‘grass’
[‘12:00’,‘3:00’,‘9:00’]
‘type’‘diet’‘times’
‘elephant’‘grass’
[‘8:00’,‘1:00’]
‘type’‘diet’‘times’
‘tortoise’‘kale’
[‘11:00’]
‘type’‘diet’‘times’
‘elephant’‘roots’
[‘5:00’,‘3:00’,‘9:00’,‘2:00’]
Common pattern
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Using a Dictionary Containing a Dict - Get
dict
‘hansa’
‘kandula’
‘lumpy’
‘surus’
keys values
>>> d[‘hansa’]
‘type’‘diet’‘times’
‘elephant’‘grass’
[‘12:00’,‘3:00’,‘9:00’]
‘type’‘diet’‘times’
‘elephant’‘grass’
[‘8:00’,‘1:00’]
‘type’‘diet’‘times’
‘tortoise’‘kale’
[‘11:00’]
‘type’‘diet’‘times’
‘elephant’‘roots’
[‘5:00’,‘3:00’,‘9:00’,‘2:00’]
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Using a Dictionary Containing a Dict - Get
dict
‘hansa’
‘kandula’
‘lumpy’
‘surus’
keys values
>>> d[‘hansa’]
{‘type’: ‘elephant’,
‘diet’: ‘grass’,
‘times’: [‘12:00’,‘3:00’,‘9:00’]}‘type’‘diet’‘times’
‘elephant’‘grass’
[‘12:00’,‘3:00’,‘9:00’]
‘type’‘diet’‘times’
‘elephant’‘grass’
[‘8:00’,‘1:00’]
‘type’‘diet’‘times’
‘tortoise’‘kale’
[‘11:00’]
‘type’‘diet’‘times’
‘elephant’‘roots’
[‘5:00’,‘3:00’,‘9:00’,‘2:00’]
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Using a Dictionary Containing a Dict - Get
dict
‘hansa’
‘kandula’
‘lumpy’
‘surus’
keys values
>>> d[‘hansa’]
{‘type’: ‘elephant’,
‘diet’: ‘grass’,
‘times’: [‘12:00’,‘3:00’,‘9:00’]}
>>> d[‘hansa’][‘type’]
‘type’‘diet’‘times’
‘elephant’‘grass’
[‘12:00’,‘3:00’,‘9:00’]
‘type’‘diet’‘times’
‘elephant’‘grass’
[‘8:00’,‘1:00’]
‘type’‘diet’‘times’
‘tortoise’‘kale’
[‘11:00’]
‘type’‘diet’‘times’
‘elephant’‘roots’
[‘5:00’,‘3:00’,‘9:00’,‘2:00’]
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Using a Dictionary Containing a Dict - Get
dict
‘hansa’
‘kandula’
‘lumpy’
‘surus’
keys values
>>> d[‘hansa’]
{‘type’: ‘elephant’,
‘diet’: ‘grass’,
‘times’: [‘12:00’,‘3:00’,‘9:00’]}
>>> d[‘hansa’][‘type’]
‘elephant’
‘type’‘diet’‘times’
‘elephant’‘grass’
[‘12:00’,‘3:00’,‘9:00’]
‘type’‘diet’‘times’
‘elephant’‘grass’
[‘8:00’,‘1:00’]
‘type’‘diet’‘times’
‘tortoise’‘kale’
[‘11:00’]
‘type’‘diet’‘times’
‘elephant’‘roots’
[‘5:00’,‘3:00’,‘9:00’,‘2:00’]
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Using a Dictionary Containing a Dict - Get
dict
‘hansa’
‘kandula’
‘lumpy’
‘surus’
keys values
>>> d[‘hansa’]
{‘type’: ‘elephant’,
‘diet’: ‘grass’,
‘times’: [‘12:00’,‘3:00’,‘9:00’]}
>>> d[‘hansa’][‘type’]
‘elephant’
>>> d[‘hansa’][‘times’]
‘type’‘diet’‘times’
‘elephant’‘grass’
[‘12:00’,‘3:00’,‘9:00’]
‘type’‘diet’‘times’
‘elephant’‘grass’
[‘8:00’,‘1:00’]
‘type’‘diet’‘times’
‘tortoise’‘kale’
[‘11:00’]
‘type’‘diet’‘times’
‘elephant’‘roots’
[‘5:00’,‘3:00’,‘9:00’,‘2:00’]
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Using a Dictionary Containing a Dict - Get
dict
‘hansa’
‘kandula’
‘lumpy’
‘surus’
keys values
>>> d[‘hansa’]
{‘type’: ‘elephant’,
‘diet’: ‘grass’,
‘times’: [‘12:00’,‘3:00’,‘9:00’]}
>>> d[‘hansa’][‘type’]
‘elephant’
>>> d[‘hansa’][‘times’]
[‘12:00’,‘3:00’,‘9:00’]
‘type’‘diet’‘times’
‘elephant’‘grass’
[‘12:00’,‘3:00’,‘9:00’]
‘type’‘diet’‘times’
‘elephant’‘grass’
[‘8:00’,‘1:00’]
‘type’‘diet’‘times’
‘tortoise’‘kale’
[‘11:00’]
‘type’‘diet’‘times’
‘elephant’‘roots’
[‘5:00’,‘3:00’,‘9:00’,‘2:00’]
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Using a Dictionary Containing a Dict - Set
dict
‘hansa’
‘kandula’
‘lumpy’
‘surus’
keys values
# for animal ‘sky’
>>> new_dict = {}
‘type’‘diet’‘times’
‘elephant’‘grass’
[‘12:00’,‘3:00’,‘9:00’]
‘type’‘diet’‘times’
‘elephant’‘grass’
[‘8:00’,‘1:00’]
‘type’‘diet’‘times’
‘tortoise’‘kale’
[‘11:00’]
‘type’‘diet’‘times’
‘elephant’‘roots’
[‘5:00’,‘3:00’,‘9:00’,‘2:00’]
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Using a Dictionary Containing a Dict - Set
dict
‘hansa’
‘kandula’
‘lumpy’
‘surus’
keys values
# for animal ‘sky’
>>> new_dict = {}
>>> new_dict[‘type’] = ‘chicken’‘type’‘diet’‘times’
‘elephant’‘grass’
[‘12:00’,‘3:00’,‘9:00’]
‘type’‘diet’‘times’
‘elephant’‘grass’
[‘8:00’,‘1:00’]
‘type’‘diet’‘times’
‘tortoise’‘kale’
[‘11:00’]
‘type’‘diet’‘times’
‘elephant’‘roots’
[‘5:00’,‘3:00’,‘9:00’,‘2:00’]
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Using a Dictionary Containing a Dict - Set
dict
‘hansa’
‘kandula’
‘lumpy’
‘surus’
keys values
# for animal ‘sky’
>>> new_dict = {}
>>> new_dict[‘type’] = ‘chicken’
>>> new_dict[‘diet’] = ‘grass’‘type’‘diet’‘times’
‘elephant’‘grass’
[‘12:00’,‘3:00’,‘9:00’]
‘type’‘diet’‘times’
‘elephant’‘grass’
[‘8:00’,‘1:00’]
‘type’‘diet’‘times’
‘tortoise’‘kale’
[‘11:00’]
‘type’‘diet’‘times’
‘elephant’‘roots’
[‘5:00’,‘3:00’,‘9:00’,‘2:00’]
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Using a Dictionary Containing a Dict - Set
dict
‘hansa’
‘kandula’
‘lumpy’
‘surus’
keys values
# for animal ‘sky’
>>> new_dict = {}
>>> new_dict[‘type’] = ‘chicken’
>>> new_dict[‘diet’] = ‘grass’
>>> new_dict[‘times’] = [‘4:00’]
‘type’‘diet’‘times’
‘elephant’‘grass’
[‘12:00’,‘3:00’,‘9:00’]
‘type’‘diet’‘times’
‘elephant’‘grass’
[‘8:00’,‘1:00’]
‘type’‘diet’‘times’
‘tortoise’‘kale’
[‘11:00’]
‘type’‘diet’‘times’
‘elephant’‘roots’
[‘5:00’,‘3:00’,‘9:00’,‘2:00’]
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Using a Dictionary Containing a Dict - Set
dict
‘hansa’
‘kandula’
‘lumpy’
‘surus’
keys values
# for animal ‘sky’
>>> new_dict = {}
>>> new_dict[‘type’] = ‘chicken’
>>> new_dict[‘diet’] = ‘grass’
>>> new_dict[‘times’] = [‘4:00’]
>>> new_dict
‘type’‘diet’‘times’
‘elephant’‘grass’
[‘12:00’,‘3:00’,‘9:00’]
‘type’‘diet’‘times’
‘elephant’‘grass’
[‘8:00’,‘1:00’]
‘type’‘diet’‘times’
‘tortoise’‘kale’
[‘11:00’]
‘type’‘diet’‘times’
‘elephant’‘roots’
[‘5:00’,‘3:00’,‘9:00’,‘2:00’]
![Page 130: Nested Data Structures - Stanford University...Nesting data structures can help us store even more information in a . Object-Oriented Programming Data structures Everyday Python Life](https://reader034.fdocuments.us/reader034/viewer/2022050101/5f40c350bd222948ad4d5ce6/html5/thumbnails/130.jpg)
Using a Dictionary Containing a Dict - Set
dict
‘hansa’
‘kandula’
‘lumpy’
‘surus’
keys values
# for animal ‘sky’
>>> new_dict = {}
>>> new_dict[‘type’] = ‘chicken’
>>> new_dict[‘diet’] = ‘grass’
>>> new_dict[‘times’] = [‘4:00’]
>>> new_dict
{‘type’: ‘chicken’, ‘diet’: ‘grass’, ‘times’: [‘4:00’]}
‘type’‘diet’‘times’
‘elephant’‘grass’
[‘12:00’,‘3:00’,‘9:00’]
‘type’‘diet’‘times’
‘elephant’‘grass’
[‘8:00’,‘1:00’]
‘type’‘diet’‘times’
‘tortoise’‘kale’
[‘11:00’]
‘type’‘diet’‘times’
‘elephant’‘roots’
[‘5:00’,‘3:00’,‘9:00’,‘2:00’]
![Page 131: Nested Data Structures - Stanford University...Nesting data structures can help us store even more information in a . Object-Oriented Programming Data structures Everyday Python Life](https://reader034.fdocuments.us/reader034/viewer/2022050101/5f40c350bd222948ad4d5ce6/html5/thumbnails/131.jpg)
Using a Dictionary Containing a Dict - Set
dict
‘hansa’
‘kandula’
‘lumpy’
‘surus’
keys values
# for animal ‘sky’
>>> new_dict = {}
>>> new_dict[‘type’] = ‘chicken’
>>> new_dict[‘diet’] = ‘grass’
>>> new_dict[‘times’] = [‘4:00’]
>>> new_dict
{‘type’: ‘chicken’, ‘diet’: ‘grass’, ‘times’: [‘4:00’]}
>>> d[‘sky’] = new_dict
‘type’‘diet’‘times’
‘elephant’‘grass’
[‘12:00’,‘3:00’,‘9:00’]
‘type’‘diet’‘times’
‘elephant’‘grass’
[‘8:00’,‘1:00’]
‘type’‘diet’‘times’
‘tortoise’‘kale’
[‘11:00’]
‘type’‘diet’‘times’
‘elephant’‘roots’
[‘5:00’,‘3:00’,‘9:00’,‘2:00’]
![Page 132: Nested Data Structures - Stanford University...Nesting data structures can help us store even more information in a . Object-Oriented Programming Data structures Everyday Python Life](https://reader034.fdocuments.us/reader034/viewer/2022050101/5f40c350bd222948ad4d5ce6/html5/thumbnails/132.jpg)
Using a Dictionary Containing a Dict - Set
dict
‘hansa’
‘kandula’
‘lumpy’
‘surus’
keys values
# for animal ‘sky’
>>> new_dict = {}
>>> new_dict[‘type’] = ‘chicken’
>>> new_dict[‘diet’] = ‘grass’
>>> new_dict[‘times’] = [‘4:00’]
>>> new_dict
{‘type’: ‘chicken’, ‘diet’: ‘grass’, ‘times’: [‘4:00’]}
>>> d[‘sky’] = new_dict
‘type’‘diet’‘times’
‘elephant’‘grass’
[‘12:00’,‘3:00’,‘9:00’]
‘type’‘diet’‘times’
‘elephant’‘grass’
[‘8:00’,‘1:00’]
‘type’‘diet’‘times’
‘tortoise’‘kale’
[‘11:00’]
‘type’‘diet’‘times’
‘elephant’‘roots’
[‘5:00’,‘3:00’,‘9:00’,‘2:00’]
‘type’‘diet’‘times’
‘chicken’‘grass’[‘4:00’]
‘sky’
![Page 133: Nested Data Structures - Stanford University...Nesting data structures can help us store even more information in a . Object-Oriented Programming Data structures Everyday Python Life](https://reader034.fdocuments.us/reader034/viewer/2022050101/5f40c350bd222948ad4d5ce6/html5/thumbnails/133.jpg)
Nested Data Structures Overview
● We can have lists in lists, dicts in lists, dicts in dicts, and so on...
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Nested Data Structures Overview
● We can have lists in lists, dicts in lists, dicts in dicts, and so on...
● Lists and dicts are mutable (and can’t be used as keys)
![Page 135: Nested Data Structures - Stanford University...Nesting data structures can help us store even more information in a . Object-Oriented Programming Data structures Everyday Python Life](https://reader034.fdocuments.us/reader034/viewer/2022050101/5f40c350bd222948ad4d5ce6/html5/thumbnails/135.jpg)
Nested Data Structures Overview
● We can have lists in lists, dicts in lists, dicts in dicts, and so on...
● Lists and dicts are mutable (and can’t be used as keys)
● Nesting data structures can help us store even more information in a
structured manner!
![Page 136: Nested Data Structures - Stanford University...Nesting data structures can help us store even more information in a . Object-Oriented Programming Data structures Everyday Python Life](https://reader034.fdocuments.us/reader034/viewer/2022050101/5f40c350bd222948ad4d5ce6/html5/thumbnails/136.jpg)
What’s next?
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Object-Oriented Programming
Object-Oriented Programming
Graphics
Images
The Console
Data structures
Everyday Python
Programming Basics
Roadmap
Life after CS106AP!
Day 1!
Midterm