Python - Dictionary and Sets

 Dictionary is a collection of key-value pairs.

Syntax:

''' a = {“key”: “value”, “marks” : “100”, “list”: [1,2,9]}

a[“key”] # Prints value

a[“list”] # Prints [1,2,9] '''

Properties of Python Dictionaries

• It is unordered
• It is mutable
• It is indexed
• Cannot contain duplicate keys

Dictionary Methods:

Consider the following dictionary,

a = {“name”: “Sri”,

“from”: “India”,

“marks”: [92,98,96]}

items() : returns a list of (key,value) tuple.

keys() : returns a list containing dictionary’s keys.

update({“friend”: “Sam”}) : updates the dictionary with supplied key-value pairs.

get(“name”) : returns the value of the specified keys (and value is returned e.g. “Sri” is returned here)

More methods are available on docs.python.org

Sets in Python:

Set is a collection of non-repetitive elements.

S= Set()          # No repetition allowed!

S.add(1)

S.add(2)

# or Set = {1,2}

Properties of Sets:

• Sets are unordered # Elements order doesn’t matter
• Sets are unindexed # Cannot access elements by index
• There is no way to change items in sets
• Sets cannot contain duplicate values

Operations on Sets:

Consider the following set:

S = {1,8,2,3}

Len(s) : Returns 4, the length of the set

remove(8) : Updates the set S and removes 8 from S

pop() : Removes an arbitrary element from the set and returns the element removed.

clear() : Empties the set S

union({8, 11}) : Returns a new set with all items from both sets. #{1,8,2,3,11}

intersection({8, 11}) : Returns a set which contains only items in both sets. #{8}

Practice:

Write a program to create a dictionary of Bengali words with values as their English translation. Provide the user with an option to look it up!

myDict={"sundar":"beautiful","nongra":"dirty","chini":"sugar"}

print("Optoons are sundar, nongra, chini:")

userInput=input("Enter a bengali word to the dictionary:\n")

print("english word is:",myDict[userInput])

Write a program to input eight numbers from the user and display all the unique numbers (once).

Answer: Use set

Can we have a set with 18(int) and “18”(str) as a value in it?

Answer: yes, because both have different types and value.

What will be the length of the following set S:

S = Set()

S.add(20)

S.add(20.0)

S.add(“20”)

What will be the length of S after the above operations?

Answer: 2

S = {}, what is the type of S?

Answer: Empty Dictionary

s={}

print(type(s))

Can you change the values inside a list which is contained in set S

S = {8, 7, 12, “Sri”, [1, 2]}

Answer: No,