PROBLEM SOLVING AND PYTHON PROGRAMMING UNIT-4

UNIT-4
LIST, TUPLES, DICTIONARIES

Lists
• An ordered group of sequences/Elements
• Separated by symbol(,)
• Enclosed inside square brackets[]
• mutable

LIST OPERATIONS and inbuilt-function
• extend()
t1=[‘a’ , ‘b’ , ‘c’]
t2=[‘d’, ‘e’]
t1.extend(t2)
print(t1)
Output:[‘a’, ‘b’, ‘c’, ‘d’, ‘e’]
• pop()
• clear()
• index()
• copy()

List loop
• Syntax:
for <list-item> in <list>
statement to process <list_item>
Example:
List=[12, ‘cyber’, 89.9]
for i in list:
print(i)
Output:
12
Cyber
89.9

Using loop with range
a = [1, 3, 5, 7, 9]
n = len(a)
for i in range(n):
print(a[i])
Output
1
3
5
7
9

Using while loop
a = [1, 3, 5, 7, 9]
i = 0
while i < len(a):
print(a[i])
i += 1
Output
1
3
5
7
9

Mutability(changeable)
>>>Number=[10,20,40]
>>>Number[2]=30
>>>print(Number)
10,20,30

Aliasing
• 2 or more variable refers to same object
>>>a=[1,2,3]
>>>b=a
>>>print(“a value=“,a)
>>>print(“b value=“,b)
>>>b.append(‘E’)
>>>print(“after aliasing”)

Aliasing
Output
a value=[1,2,3]
b value=[1,2,3]
after aliasing
a value=[1,2,3,E]
b value=[1,2,3,E]

Cloning list
• Make copy of list itself, not just the reference
• Slice operator is used for cloning
>>>a=[1,2,3]
>>>b=a[:]
>>>b.append(‘E’)
>>>print(“after cloning”)

cloning
Output
a value=[1,2,3]
b value=[1,2,3]
after cloning
a value=[1,2,3]
b value=[1,2,3,E]

List Parameters
• Passing list as argument
def delete_header(t):
del [0]
letters=[‘a’, ‘b’, ‘c’]
delete_header(letters)
print(letters)
Output:
[‘b’ , ‘c]

TUPLE- finite, static, immutable sequence of values
TUPLE VALUES:any data type
Enclosed within ( ): ex t=(5,’a,25.5)
• Creating tuple
– Create with single
element
>>>t=‘a’
• Built-in function
>>>t=tuple()
• Sequence
>>> t=tuple(‘hai’)
>>>print(t)
(‘h’,’a’,’i’)
Operations on tuple
>>>t=(‘h’ ,’a’, ‘i’)
>>>t[0]
‘h’
>>>t[2]
‘i’
>>> t[1:2] #Slice
(‘a’, ‘i’)
>>>t[0]=‘A’
#error(immutable)
>>>t(‘A’)+t[1:]
>>>t
(‘A’, ‘a’, ‘i’)

Tuple illustration
• Tuple assignment
>>>t1=(10,20)
>>>t2=(30,40)
t1,t2=t2,t1
Print(t1) 30,40
Print(t2)10,20
No.of value on left and
right must be equal
t1,t2=t2,t1,t3 #error
t3,t2,t1=t2,t1,t3
• T=()
print(T)
• T=((1,2,3),’hello’,56.7, [8,4,6]) -mixed datatype
print(T)
• T=(‘p’,’y’,’t’,’h’,’o’,’n’)
print(T[3])h
Print(T[1:4])(’y’,’t’,’h’)
Print(T[:])(‘p’,’y’,’t’,’h’,’o’,’n’)
Print(T[4:])(’o’,’n’)
print(T[-1])n
print(T[-4])t
• T1=(“mouse”,[8,6,4],(1,2,3))
print(T1[0][3]) -s
print(T1[1][1])6

Tuples with return value
def circleinfo(r):
c=2*3.14*r
a=3.14*r*r
return (c,a)
r=int(input(“Enter the radius”))
print(circleinfo(r))

Dictionaries(mappings)
• Data structure-immutable
• Values are stored as {key:value} pair
Syntax:
• dic_name={key1:value1,key2:value2}
Hashing:
key value converts into index value
used for accessing values in specific
location

Creation of dictionaries
Method1: creating empty dictionary using {}
A = {}
print("Empty Dictionary: ")
print(A)
Method 2:using literal notation(key value pair)
A = {1: 'Geeks', 2: 'For', 3: 'Geeks'}
print("nDictionary with the use of key-value: ")
print(A)
Method 3:using dict()
Dict = dict([(1, 'Geeks'), (2, 'For')])
print("nDictionary using dict(): ")
print(Dict)

Adding items into dictionary
>>>cyber={}
>>>print (cyber)
{}
>>>cyber[‘name’]=‘priya’
>>>cyber[‘age’]=18
>>>print(cyber)
{‘name’:’priya’, ‘age’:18}

Accessing items from dictionary
>>>cyber={‘name’:’Priya’, ‘age’:19}
>>>print(cyber[‘name’])
Priya
>>>print(cyber.get(‘age’))
19

Printing dictionary
>>> cyber={‘name’:’Priya’, ‘age’:19}
>>>for x in cyber:
print(x, “:” ,cyber[x])
Output:
name:Priya
age:19

Operation and Methods in Dictionary
• dict()
• dict(s)
• len(d)
• d[key]=value
• del d[key]
• key in d
• values(),keys(),sorted()

PROBLEM SOLVING AND PYTHON PROGRAMMING UNIT-4

PROBLEM SOLVING AND PYTHON PROGRAMMING UNIT-4

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