CSE 231 Lab 9

Nested Dictionaires sets 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': ‘Imen', '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'] {'name': 'Imen', 'age': '40', 'sex': 'Female', 'married': 'Yes'} {'name': 'Imen', 'age': '40', 'sex': 'Female'}

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])

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.

{'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'}

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

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

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

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

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

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)

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)

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}