Python list tuple dictionary .pptx

UNIT – IV
LISTS, TUPLES, DICTIONARIES
Lists: list operations, list slices, list methods, list loop, mutability, aliasing, cloning lists, list
parameters, list comprehension; Tuples: tuple assignment, tuple as return value, tuple
comprehension; Dictionaries: operations and methods, comprehension;
Lists, Tuples, Dictionaries:
List:
 It is a general purpose most widely used in data structures
 List is a collection which is ordered and changeable and allows duplicate members.
(Grow and shrink as needed, sequence type, sortable).
 To use a list, you must declare it first. Do this using square brackets and separate
values with commas.
 We can construct / create list in many ways.
Ex:
>>> list1=[1,2,3,'A','B',7,8,[10,11]]
>>> print(list1)
[1, 2, 3, 'A', 'B', 7, 8, [10, 11]]
>>> x=list()
>>> x
[]
>>>
tuple
1=(1,
2,3,4)
>>>
x=list
(tuple
1)
>>> x
[1, 2,
3, 4]

List operations:
These operations include indexing, slicing, adding, multiplying, and checking
for membership
Basic List Operations:
Lists respond to the + and * operators much like strings; they mean concatenation and
repetition here too, except that the result is a new list, not a string.
Python Expression Results Description
len([1, 2, 3]) 3 Length
[1, 2, 3] + [4, 5, 6] [1, 2, 3, 4, 5, 6] Concatenation
['Hi!'] * 4 ['Hi!', 'Hi!', 'Hi!', 'Hi!'] Repetition
3 in [1, 2, 3] True Membership
for x in [1, 2, 3]: print x, 1 2 3 Iteration
Indexing, Slicing, and Matrixes
Because lists are sequences, indexing and slicing work the same way for lists as they do
for strings.
Assuming following input −
L = ['mrcet', 'college', 'MRCET!']
Python Expression Results Description
L[2] MRCET Offsets start at zero

L[-2] college Negative: count from the right
L[1:] ['college', 'MRCET!'] Slicing fetches sections
List slices:
>>> list1=range(1,6)
>>> list1
range(1,
6)
>>> print(list1)
range(1, 6)
>>>
list1=[1,2,3,4,5
,6,7,8,9,10]
>>> list1[1:]
[2, 3, 4, 5, 6, 7,
8, 9, 10]
>>> list1[:1]
[1]
>>> list1[2:5]
[3, 4, 5]
>>> list1[:6]
[1, 2, 3, 4, 5,
6]
>>> list1[1:2:4]
[2]
>>> list1[1:8:2]
[2, 4, 6, 8]
List methods:
The list data
type has some
more methods.

 Append()
 Extend()
 Insert()
 Pop()
 Remove()
 Reverse()
 Sort()
Delete: Delete a list or an item from a list
>>> x=[5,3,8,6]
#deletes the index position 1 in a
list
>>> del(x[1])
>>> x
[5, 8,
6]
>>> del(x)
>>> x # complete list gets deleted
Append: Append an item to a list
>>> x=[1,5,8,4]
>>> x.append(10)
>>> x
[1, 5, 8, 4, 10]
Extend: Append a sequence to a list.
>>> x=[1,2,3,4]
>>> y=[3,6,9,1]
>>> x.extend(y)
>>> x
[1, 2, 3, 4, 3, 6, 9, 1]
Insert: To add an item at the specified index, use the insert () method:
>>> x=[1,2,4,6,7]

>>> x.insert(2,10) #insert(index no, item to be inserted)
>>> x
[1, 2, 10, 4, 6, 7]
>>> x.insert(4,['a',11])
>>> x
[1, 2, 10, 4, ['a', 11], 6, 7]
Pop: The pop() method removes the specified index, (or the last item if index is
not specified) or simply pops the last item of list and returns the item.
>>> x=[1, 2, 10, 4, 6, 7]
>>> x.pop()
7
>>> x
[1, 2, 10, 4,
6]
>>> x=[1,
2, 10, 4, 6]
>>> x.pop(2)
10
>>> x
[1, 2, 4, 6]
Remove:
The
remove()
method
removes the
specified
item from a
given list.
>>>
x=[1,33,2,10,
4,6]

[1, 2, 10, 4, 6]
>>> x.remove(4)
>>> x
[1, 2, 10, 6]
Reverse: Reverse the order of a given list.
>>> x=[1,2,3,4,5,6,7]
>>> x.reverse()
>>> x
[7, 6, 5, 4, 3, 2, 1]
Sort: Sorts the elements in ascending order
>>> x=[7, 6, 5, 4, 3, 2, 1]
>>> x.sort()
>>> x
[1, 2, 3, 4, 5, 6, 7]
>>> x=[10,1,5,3,8,7]
>>> x.sort()
>>> x
[1, 3, 5, 7, 8, 10]
List loop:
Loops are control structures used to repeat a given section of code a certain number of
times or until a particular condition is met.
Method #1: For loop
#list of items
list = ['M','R','C','E','T']

i = 1
#Iterating over the
list for item in list:
print ('college ',i,' is
',item) i = i+1
Output:
C:/Users/MRCET/AppData/Local/Programs/Python/Python38-32/pyyy/lis.py
college 1 is M
college 2 is R
college 3 is
C
college 4 is E
college 5 is T
Method #2:
For loop and
range()
In case we want to use the traditional for loop which iterates from number x to number y.
# Python3 code to iterate over a list
list = [1, 3, 5, 7, 9]
# getting length of
list length = len(list)
# Iterating the index
# same as 'for i in range(len(list))'
for i in range(length):
print(list[i])
Output:
C:/Users/MRCET/AppData/Local/Programs/Python/Python38-32/pyyy/listlooop.py
1
3
5
7
9
Method #3: using while loop
# Python3 code to iterate over a
list list = [1, 3, 5, 7, 9]
# Getting length of list

length = len(list)
i = 0
# Iterating using while
loop while i < length:
print(list[i])
i += 1
Tuples:
A tuple is a collection which is ordered and unchangeable. In Python tuples are written
with round brackets.
 Supports all operations for sequences.
 Immutable, but member objects may be mutable.
 If the contents of a list shouldn’t change, use a tuple to prevent items from
accidently being added, changed, or deleted.
 Tuples are more efficient than list due to python’s implementation.
We can construct tuple in many ways:
X=() #no item tuple
X=(1,2,3)
X=tuple(list1)
X=1,2,3,4
Example:
>>> x=(1,2,3)
>>> print(x)
(1, 2, 3)
>>> x
(1, 2,
3)
>>>
x=()
>>> x
()
>>>
x=[4,
5,66,
9]
>>>
y=tup
le(x)
>>> y

(4, 5, 66, 9)
>>> x=1,2,3,4
>>> x
(1, 2, 3, 4)
Some of the operations of tuple are:
 Access tuple items
 Change tuple items
 Loop through a tuple
 Count()
 Index()
 Length()
Access tuple items: Access tuple items by referring to the index number, inside square
brackets
>>> x=('a','b','c','g')
>>>
print(x[2]) c
Change tuple items: Once a tuple is created, you cannot change its values. Tuples
are unchangeable.
>>> x=(2,5,7,'4',8)
>>> x[1]=10
Traceback (most recent call last):
File "<pyshell#41>", line 1, in <module>
x[1]=10
TypeError: 'tuple' object does not
support item assignment
>>> x
(2, 5, 7, '4', 8) # the value is still the
same
Loop through a tuple: We can loop the
values of tuple using for loop
>>> x=4,5,6,7,2,'aa'
>>> for i in x:
print(i)

4
5
6
7
2
aa
Count (): Returns the number of times a specified value occurs in a tuple
>>> x=(1,2,3,4,5,6,2,10,2,11,12,2)
>>> x.count(2)
4
Index (): Searches the tuple for a specified value and returns the position of where it
was found
>>> x=(1,2,3,4,5,6,2,10,2,11,12,2)
>>> x.index(2)
1
(Or)
>>>
x=(1,2,3,4,5,6,
2,10,2,11,12,2)
>>>
y=x.index(2)
>>> print(y)
1
Length ():
To know the
number of
items or
values
present in a
tuple, we
use len().
>>>
x=(1,2,3,4,5
,6,2,10,2,11,
12,2)
>>>
y=len(x)
>>> print(y)
12

Dictionaries:
A dictionary is a collection which is unordered, changeable and indexed. In
Python dictionaries are written with curly brackets, and they have keys and
values.
 Key-value pairs
 Unordered
We can construct or create dictionary like:
X={1:’A’,2:’B’,3:’c’}
X=dict([(‘a’,3) (‘b’,4)]
X=dict(‘A’=1,’B’ =2)
Example:
>>> dict1 =
{"brand":"mrcet","mo
del":"college","year":2
004}
>>> dict1
{'brand': 'mrcet',
'model': 'college',
'year': 2004}
Operations and
methods:
Methods that are available with dictionary are tabulated below. Some of them have already
been used in the above examples.
Below are some dictionary operations:
Method Description
clear() Remove all items form the dictionary.

copy() Return a shallow copy of the dictionary.
fromkeys(seq[, v])
Return a new dictionary with keys from seq and
value equal to v (defaults to None).
get(key[,d])
Return the value of key. If key doesnot exit,
return d (defaults to None).
items()
Return a new view of the dictionary's
items (key, value).
keys() Return a new view of the dictionary's keys.
pop(key[,d])
Remove the item with key and return its value
or d if key is not found. If d is not provided
and key is not found, raises KeyError.
popitem()
Remove and return an arbitary item (key,
value). Raises KeyError if the dictionary is
empty.
setdefault(key[,d])
If key is in the dictionary, return its value. If
not, insert key with a value of d and
return d (defaults to None).
update([other])
Update the dictionary with the key/value
pairs from other, overwriting existing keys.
values() Return a new view of the dictionary's values

Below are some dictionary operations:
To access specific value of a dictionary, we must pass its key,
>>> dict1 = {"brand":"mrcet","model":"college","year":2004}
>>> x=dict1["brand"]
>>> x
'mrcet'
To access keys and values and items of dictionary:
>>> dict1.keys()
dict_keys(['brand', 'model', 'year'])
>>> dict1.values()
dict_values(['mrcet', 'college',
2004])
>>> dict1.items()
dict_items([('brand', 'mrcet'),
('model', 'college'), ('year', 2004)])
>>> for items in dict1.values():
print(items)
mrcet
college
2004
>>> for items in dict1.keys():
print(items)
brand
model
year
>>> for i in
dict1.items():
print(i)
('brand', 'mrcet')
('model', 'college')
('year', 2004)

Some more operations like:
 Add/change
 Remove
 Length
 Delete
Add/change values: You can change the value of a specific item by referring to its key
name
>>> dict1["year"]=2005
>>> dict1
{'brand': 'mrcet', 'model': 'college', 'year': 2005}
Remove(): It removes or pop the specific item of dictionary.
>>> print(dict1.pop("model"))
college
>>> dict1
{'brand': 'mrcet', 'year': 2005}
Delete: Deletes a particular
item.
>>> x = {1:1, 2:4, 3:9, 4:16,
5:25}
>>> del x[5]
>>> x
Length: we use len() method
to get the length of dictionary.
>>>{1: 1, 2: 4, 3: 9, 4: 16}
{1: 1, 2: 4, 3: 9, 4: 16}
>>> y=len(x)
>>> y
4
Iterat
ing
over
(key,
value
)
pairs
:
>>> x
=
{1:1,

2 4
3 9
4 16
5 25
>>> for k,v in x.items():
print(k,v)
1 1
2 4
3 9
4 16
5 25
List of Dictionaries:
>>> customers =
[{"uid":1,"name":"John
"},
{"uid":2,"name":"Smith"
},
{"uid":3,"name":"Ande
rsson"},
]
>>> >>>
print(customers)
[{'uid': 1, 'name': 'John'},
{'uid': 2, 'name':
'Smith'}, {'uid': 3,
'name': 'Andersson'}]
## Print the uid and
name of each customer
>>> for x in customers:
print(x["uid"], x["name"])
1 John
2 Smith
3 Andersson
## Modify an entry, This will
change the name of customer 2
from Smith to Charlie
>>> customers[2]
["name"]="charlie"
>>> print(customers)
[{'uid': 1, 'name': 'John'}, {'uid':

[{'uid': 1, 'name': 'John', 'password': '123456'}, {'uid': 2, 'name': 'Smith', 'password':
'123456'}, {'uid': 3, 'name': 'charlie', 'password': '123456'}]
## Delete a field
>>> del customers[1]
[{'uid': 1, 'name': 'John', 'password': '123456'}, {'uid': 3, 'name': 'charlie', 'password':
'123456'}]
>>> del customers[1]
[{'uid': 1, 'name': 'John', 'password': '123456'}]
## Delete all fields
>>> for x in customers:
del x["uid"]
>>> x
{'name': 'John',
'password': '123456'}

Python list tuple dictionary .pptx

Python list tuple dictionary .pptx

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Python list tuple dictionary .pptx