2 UNIT CH3 Dictionaries v1.ppt

Python Dictionary
• The dictionary itself is an abstract datatype.
• In this it contains a group of data with the different data types.
• And each data is stored as a key-value pair, that key is used to
identify that data.
• We can add or replace values of the dictionary, it is mutable.
• But the key associated with the dictionary can't be changed.
• Therefore, the keys are immutable or unique.

The syntax provides useful type information. The square brackets indicate that it’s a
list. The parenthesis indicate that the elements in the list are tuples.

Aliasing and copy using function- copy()

Which of the following statements create a
dictionary?
a) d = {}
b) d = {“john”:40, “peter”:45}
c) d = {40:”john”, 45:”peter”}
d) All of the mentioned

Items are accessed by their position in a dictionary
and All the keys in a dictionary must be of the same
type.
a. True
b. False

Dictionary keys must be immutable
a. True
b. False

In Python, Dictionaries are immutable
a. True
b. False

What will be the output of the following Python code snippet?
a={1:"A",2:"B",3:"C"}
for i,j in a.items():
print(i,j,end=" ")
a) 1 A 2 B 3 C
b) 1 2 3
c) A B C
d) 1:”A” 2:”B” 3:”C”

Select the correct way to print Emma’s age.
student = {1: {'name': 'Emma', 'age': '27', 'sex': 'Female'},
2: {'name': 'Mike', 'age': '22', 'sex': 'Male'}}
a. student[0][1]
b. student[1]['age']
c. student[0]['age']
d. student[2]['age']

Fibonacci using Dictionary
fib={0:0,1:1}
def fibo(n):
if(n==0):
return 0
if(n==1):
return 1
else:
for i in range(2, n+1):
fib[i]=fib[i-1]+fib[i-2]
return(fib)
print(fibo(5))

Use get()
The get() method returns the value of the item with the specified key.
Syntax:
dictionary.get(keyname, value)

Iterate over Python dictionaries using for loops
d={'red':1,'green':2,'blue':3}
for color_key, value in d.items():
print(color_key,'corresponds to', d[color_key])
OUTPUT:
blue corresponds to 3
green corresponds to 2
red corresponds to 1
Remove a key from a Python dictionary
myDict = {'a':1,'b':2,'c':3,'d':4}
print(myDict)
if 'a' in myDict:
del myDict['a']
print(myDict)

OUTPUT:
{'d': 4, 'a': 1, 'b': 2, 'c': 3}
{'d': 4, 'b': 2, 'c': 3}
Sort a Python dictionary by key
color_dict = {'red':'#FF0000',
'green':'#008000',
'black':'#000000',
'white':'#FFFFFF‘
}
for i in sorted(color_dict):
print(key,” :”, color_dict[ i ]))
OUTPUT:
black: #000000
green: #008000
red: #FF0000
white: #FFFFFF

• Use update() on dictionary

• The pop() method removes the specified item from the dictionary.
• The popitem() method removes the item that was last inserted into
the dictionary. In versions before 3.7, the popitem() method removes
a random item.

Find the maximum and minimum value of a Python dictionary

Concatenate two Python dictionaries into a new one
dic1={1:10, 2:20}
dic2={3:30, 4:40}
dic3={5:50,6:60}
dic4 = {}
for d in (dic1, dic2, dic3):
dic4.update(d)
print(dic4)
OUTPUT:
{1: 10, 2: 20, 3: 30, 4: 40, 5: 50, 6: 60}

Test whether a Python dictionary contains a specific key
fruits = {}
fruits["apple"] = 1
fruits["mango"] = 2
fruits["banana"] = 4
if "mango" in fruits:
print("Has mango")
else:
print("No mango")
if "orange" in fruits:
print("Has orange")
else:
print("No orange")
OUTPUT:
Has mango
No orange

QUESTIONS
Q1:Write a Python script to add a key to a dictionary.
Sample Dictionary : {0: 10, 1: 20}
Expected Result : {0: 10, 1: 20, 2: 30}
Q2: Write a Python script to concatenate following dictionaries to create a new one.
Sample Dictionary :
dic1={1:10, 2:20}
dic2={3:30, 4:40}
dic3={5:50,6:60}
Expected Result : {1: 10, 2: 20, 3: 30, 4: 40, 5: 50, 6: 60}
Q3: Write a Python script to check if a given key already exists in a dictionary.
Q4: Write a Python script to print a dictionary where the keys are numbers between 1 and 15 (both included) and
the values are square of keys.
Sample Dictionary
{1: 1, 2: 4, 3: 9, 4: 16, 5: 25, 6: 36, 7: 49, 8: 64, 9: 81, 10: 100, 11: 121, 12: 144, 13: 169, 14: 196, 15: 225}

• #Add two dictionaries and get
results.
• #concatenate dictionaries
• d1={'A':1000,'B':2000}
• d2={'C':3000}
• d1.update(d2)
• print("Concatenated dictionary is:")
• print(d1)
• o/p: Concatenated dictionary is:
• {'A': 1000, 'B': 2000, 'C': 3000}
#concatenate dictionaries
dic1={1:10, 2:20}
dic2={3:30, 4:40}
dic3={5:50,6:60}
dic4 = {}
for i in (dic1, dic2, dic3):
dic4.update(i)
print(dic4)
o/p:
{1: 10, 2: 20, 3: 30, 4: 40, 5: 50, 6: 60}

#Q3: Write a Python script to check if a given key already
exists in a dictionary.
d = {1: 10, 2: 20, 3: 30, 4: 40, 5: 50, 6: 60}
def present(i):
if i in d:
print(i ,' key is present in the dictionary')
else:
print(i, 'key is not present in the dictionary')
present(20)
present(3)
o/p:
20 key is not present in the dictionary
3 key is present in the dictionary
##sum and multiplication of dictionary
elements
d = {1: 10, 2: 20, 3: 1, 4: 1, 5: 1, 6: 1}
print(sum(d.values()))
mul=1
for i in d:
mul = mul * d[i]
print("Multiplication is", mul)
#

Use of __setitem__ ( )
• myDict = {1:100, 2:200}
• myDict.__setitem__(33,300)
• myDict
• {1: 100, 2: 200, 33: 300}

Add user input() in a dictionary
• d = { }
• for i in range(3):
– i = input(“enter Key")
– j = input(“enter value")
– d[i] = j
print(d)

Take dictionary items() from user

Q6: Write a Python script to merge two Python dictionaries.
Q7: Write a Python program to sum all the items in a dictionary.
Q8: Write a Python program to multiply all the items in a dictionary.
Q9: Write a Python program to remove a key from a dictionary.
Q10: Write a Python program to remove duplicates from Dictionary.
Q11: Write a Python program to create and display all combinations of letters, selecting each letter from a
different key in a dictionary.
Sample data : {'1':['a','b'], '2':['c','d']}
Expected Output:
ac
ad
bc
bd

Q9: Write a Python program to remove a key from
a dictionary.
• d = {'a':100, 'b':200, 'c':300, 'd':400}
• del d['a']
• >>>d
• {'b': 200, 'c': 300, 'd': 400}

# Use function and print players details of a dictionary
def indian_cricket(d):
for i in d:
print("Details of Players are", d[i])
ind = {'test1':{'Dhoni':75, 'Kohli':170 }, 'test2':{'Dhoni':30, 'Pujara': 45} }
indian_cricket(ind)
o/p
Details of Players are {'Dhoni': 75, 'Kohli': 170}
Details of Players are {'Dhoni': 30, 'Pujara': 45}

• Define a python function ‘indian_cricket(d)’ which reads a dictionary
of the following form and identifies the player with the highest total
score. The function should return a pair (, topscore), where
playername is the name of the player with the highest score and
topscore is the total runs scored by the player.
Input is:
indian_cricket (
{‘test1’:{‘Dhoni’:75, ‘Kohli’:170},
‘test2’:{Dhoni’: 30, ‘Pujara’: 45}
})

• maxdic={}
• dic={'test1':{'Dhoni':75, 'Kohli':170 },
• 'test2':{'Dhoni':30, 'Pujara': 45}
• }
• for keymain,valuemain in dic.items(): #keymain is test1 , test ... keys
• max=0
• key1=''
• dicin={}
• for key,value in valuemain.items():
• if(value>max):
• max=value
• key1=key
• dicin[key1]=max #key1 is used for Dhoni, kohli, Pujara
• maxdic[keymain]=dicin
• print("Topscore Player wise in different Tests is", maxdic)

2 UNIT CH3 Dictionaries v1.ppt

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