CSE 231 Lab 9 Topics to - PowerPoint Presentation

Slide1

CSE 231

Lab 9

Topics to

cover

Nested

Dictionaires

sets

What

is Nested Dictionary?

A dictionary inside a dictionary

Creating a nested dictionary:

people = {1: {'name': ‘Zach', 'age': '7', 'sex': 'Male'}, 2: {'name': ‘Ann', 'age': ‘40', 'sex': 'Female'}} print(people[1]['name'])print(people[1]['age'])print(people[1]['sex'])

Zach

7

Male

What

is Nested Dictionary?

Modifying

a nested dictionary:

people[2]['married'] = 'Yes‘ print(people[2])del people[2]['married'] print(people[2])

{'name':

‘Ann',

'age': '40', 'sex': 'Female', 'married': 'Yes'}

{'name':

‘Ann', 'age': '40', 'sex': 'Female'}

people

=

{1: {'name': ‘Zach', 'age': '7', 'sex': 'Male'},

2

: {'name': ‘Ann', 'age': ‘40', 'sex': 'Female'}}

What

is Nested Dictionary?

Iterating through a nested dictionary:

for id, info in people.items(): print("\nPerson ID:", id)

for key in info

: print(key

+ ':', info[key])

Person ID: 1

name: Zach

age: 7

sex: Male

Person ID: 2

name:

Ann

age: 40

sex:

Female

people

=

{1: {'name': ‘Zach', 'age': '7', 'sex': 'Male'},

2

: {'name': ‘Ann', 'age': ‘40', 'sex': 'Female'}}

Sets

Think of mathematics

.

All items in a set are unique (no duplicates).

Unordered Collection of unique objectsLast data structureUse { } just like dictionariesBut not key:value pairs

Example: { 1, 2, 3 }The set doesn’t maintain elements in any particular order.

Create and update a Set

Creating a

set

S

= set() # S = { } creates a dictionary!S = { 20, 5, 10 }S = set(“abcabbcd”) # Works with any iterable, ignores duplicatesset comprehensions are also supported:

{'b', 'd', 'a', 'c'}

p

rint(S)

S = {x for x in 'abracadabra' if x not in 'abc'}

print(S)

{'r', 'd'}

Create and update a Set

Creating a

set

A

= {1, 2, 3} B = { 3, 2, 3, 1}print(A == B)

True #A 

and B are equal sets

The order of elements is unimportant and duplicates are removed

Create and update a Set

S = {'b', 'd', 'a', 'c'}

Adding/discarding an object

S.add

(100) # adds the object, ignores duplicates

S.discard

(100) # discards the object if it exists

S.remove

(100) # removes the object from set, but raises

KeyError

if the object doesn’t exist!

{'b', 100, 'd', 'a', 'c'}

p

rint(S

)

{'b',

'd

', 'a', 'c'}

p

rint(S

)

KeyError

: 100

p

rint(S

)

Patterns

Ints

:

x = 0 #

initialize at zerox += 1 # increment the counterStrings:s = ‘’ # initialize with empty strings += ch # concatenate characters Lists:L = [] # initialize with empty listL.append(value) # append values to the list

Patterns

Dictionaries:

D = { } #

initialize with empty

dictionaryS = “aabacdbacd” # we have a string, we want to count all the charactersfor ch in S: if ch in D: # check to see if the key exists in the dictionary D[ch] += 1 # increment the value if it exists else: D[ch] = 1 # set the value to 1 if it doesn’t exist

Patterns

Sets:

We have

a dictionary

file and we want to create a set of all its wordsS = set() # initialize with empty setfp = open(“dictionary.txt”)for line in fp: set.add(line.strip()) # add the word to the set, it ignores the duplicates

Useful Function, Methods & Operators

l

en

(S) returns the size of the set

check whether an element belongs to a set using the keyword in Union:set_a | set_bset_a.union(set_b)Intersection:set_a & set_bset_a.intersection(set_b)

Useful Function, Methods & Operators

Symmetric_Difference

: the set of elements in precisely one of

set_a

or set_bSet_a ^ set_bDifference: the set of elements in set_a but not set_bset_a - set_bset_a.difference(set_b)

Sets examples

A

= {1, 2, 3, 4, 5}

B

= {4, 5, 6, 7, 8}print(A | B)print(A & B)print(A - B) print(B - A) print(A ^ B)

{1, 2, 3, 4, 5, 6, 7, 8}

{4, 5}

{1, 2, 3}

{1, 2, 3, 6, 7, 8}

{8, 6, 7}