1. CSE 231 Lab 9

2. Nested Dictionaires sets
Topics to cover
Nested Dictionaires
sets

3. What is Nested Dictionary?
A dictionary inside a dictionary
Creating a nested dictionary:
people = {1: {'name': ‘Zach', 'age': '7', 'sex': 'Male'},
2: {'name': ‘Imen', 'age': ‘40', 'sex': 'Female'}}
print(people[1]['name'])
print(people[1]['age'])
print(people[1]['sex'])
Zach 7
Male

4. What is Nested Dictionary?
Modifying a nested dictionary:
people[2]['married'] = 'Yes‘
print(people[2])
del people[2]['married']
{'name': 'Imen', 'age': '40', 'sex': 'Female', 'married': 'Yes'}
{'name': 'Imen', 'age': '40', 'sex': 'Female'}

5. What is Nested Dictionary?
Person ID: 1
name: Zach
age: 7
sex: Male
Person ID: 2
name: Imen
age: 40
sex: Female
Iterating through a nested dictionary:
for id, info in people.items():
print("\nPerson ID:", id)
for key in info:
print(key + ':', info[key])

6. Sets Think of mathematics.
All items in a set are unique (no duplicates).
Unordered Collection of unique objects
Last data structure
Use { } just like dictionaries
But not key:value pairs
Example: { 1, 2, 3 }
The set doesn’t maintain elements in any particular order.

7. {'b', 'd', 'a', 'c'} {'r', 'd'} 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 duplicates
set comprehensions are also supported:
Print(S)
{'b', 'd', 'a', 'c'}
S = {x for x in 'abracadabra' if x not in 'abc'}
Print(S)
{'r', 'd'}

8. True #A and B are equal sets
Create and update a Set
Creating a set
A = {1, 2, 3}
B = { 3, 2, 3, 1}
True #A and B are equal sets
Print(A == B)
The order of elements is unimportant and duplicates are removed

9. Create and update a Set 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!
Print(S)
{'b', 100, 'd', 'a', 'c'}
Print(S)
{'b', 'd', 'a', 'c'}
Print(S)
KeyError: 100

10. Patterns Ints: Strings: Lists: x = 0 # initialize at zero
x += 1 # increment the counter
Strings:
s = ‘’ # initialize with empty string
s += ch # concatenate characters
Lists:
L = [] # initialize with empty list
L.append(value) # append values to the list

11. Patterns Dictionaries: D = { } # initialize with empty dictionary
S = “aabacdbacd” # we have a string, we want to count all the characters
for 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

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

13. Useful Function, Methods & Operators
len(S) returns the size of the set
check whether an element belongs to a set using the keyword in
Union:
set_a | set_b
set_a.union(set_b)
Intersection:
set_a & set_b
set_a.intersection(set_b)

14. Useful Function, Methods & Operators
Symmetric_Difference: the set of elements in precisely one of set_a or set_b
Set_a ^ set_b
Difference: the set of elements in set_a but not set_b
set_a - set_b
set_a.difference(set_b)

15. 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}
{8, 6, 7}
{1, 2, 3, 6, 7, 8}