Python Variable Types, List, Tuple, Dictionary

Assigning Values to Variables
• It doesn’t need explicit declaration to reserve memory space.
• Declaration happens automatically when we assign values to variable.
counter = 100 # An integer assignment
miles = 1000.0 # A floating point
name = "John" # A string
print counter
print miles
print name

Multiple Assignment
• Single value for multiple variables
• Multiple values for multiple variables in single assignment line.
a = b = c = 100
a = b = c = 1, “john2”, "John

Standard Data Types
• Five standard datatypes
1. Numbers
2. String
3. List
4. Tuple
5. Dictionary

Number
• It store numeric values.
• Number object is created when we assign a value to them.
• To delete variable, use keyword del
var1 = 1
var2 = 10
del var1

Number
• Python support four different numeric types.
1. int – signed integer.
2. long – long integer, also represent octal and hexadecimal.
3. float – floating point real values.
4. complex – complex values.

String
• It represented inside of quotation marks.
• Quotes: single or double.
• Subset of string can be taken by using slice operator [ ] and [ : ] with indexes 0 : -1
• Concatenation operator plus ( + ) sign.
• Replication operator star ( * ) sign.

String
str = 'Hello World!’
print str # Prints complete string
print str[0] # Prints first character of the string
print str[2:5] # Prints characters starting from 3rd to 5th
print str[2:] # Prints string starting from 3rd character
print str * 2 # Prints string two times
print str + "TEST" # Prints concatenated string

List - Create list
# empty list
my_list = []
# list of integers
my_list = [1, 2, 3]
# list with mixed datatypes
my_list = [1, "Hello", 3.4]
# nested list
my_list = ["mouse", [8, 4, 6], ['a']]

my_list = ['p','r','o','b','e']
print(my_list[0]) # Output: p
print(my_list[2]) # Output: o
print(my_list[4]) # Output: e
print(my_list[-1]) # Output: e
print(my_list[-5]) # Output: p
n_list = ["Happy", [2,0,1,5]]
print(n_list[0][1]) # Output: a
print(n_list[1][3]) # Output: 5
List – Access list element

my_list = ['p','r','o','g','r','a','m','i','z']
# elements 3rd to 5th
print(my_list[2:5])
# elements beginning to 4th
print(my_list[:-5])
# elements 6th to end
print(my_list[5:])
# elements beginning to end
print(my_list[:])
List – Access list element

List – Change or Add elements
# mistake values
odd = [2, 4, 6, 8]
odd[0] = 1 # change the 1st item
print(odd) # Output: [1, 4, 6, 8]
odd[1:4] = [3, 5, 7]
print(odd) # Output: [1, 3, 5, 7]
odd = [1, 3, 5]
odd.append(7)
print(odd)
# Output: [1, 3, 5, 7]
odd.extend([9, 11, 13])
print(odd)
# Output: [1, 3, 5, 7, 9, 11, 13]

List – Delete elements
my_list = ['p','r','o','b','l','e','m’]
del my_list[2] # delete one item
print(my_list) # Output: ['p', 'r', 'b', 'l', 'e', 'm']
del my_list[1:5] # delete multiple items
print(my_list) # Output: ['p', 'm']
del my_list # delete entire list
print(my_list) # Error: List not defined

List Method – append()
• It is used to add elements to the last position of List.
List = ['Mathematics', 'chemistry', 1997, 2000]
List.append(20544)
print(List)
['Mathematics', 'chemistry', 1997, 2000, 20544]

List Method – insert()
List = ['Mathematics', 'chemistry', 1997, 2000]
List.insert(2,10087)
print(List)
• It is used to insert element at specific position.
['Mathematics', 'chemistry’, 10087, 1997, 2000]

List Method – extend()
• Add multiple values or another list into the end of the current list
List1 = [1, 2, 3]
List2 = [2, 3, 4, 5]
# Add List2 to List1
List1.extend(List2)
print(List1)
#Add List1 to List2 now
List2.extend(List1)
print(List2)
[1, 2, 3, 2, 3, 4, 5]
[2, 3, 4, 5, 1, 2, 3, 2, 3, 4, 5]

List Method – sum(), count(), len(), min(), max()
List = [1, 2, 3, 4, 5 , 1]
print(sum(List)) //16
print(List.count(1)) //2
print(len(List)) //6
print(min(List)) //1
print(max(List)) //5

List Method – sort(), reverse()
List = [2.3, 4.445, 3, 5.33, 1.054, 2.5]
#Reverse flag is set True
List.sort(reverse=True)
print(List)
sorted(List)
print(List)
[5.33, 4.445, 3, 2.5, 2.3, 1.054]
[1.054, 2.3, 2.5, 3, 4.445, 5.33]

List Method – pop(), del(), remove()
pop(): Index is not a necessary parameter, if not mentioned takes the last index.
del() : Element to be deleted is mentioned using list name and index.
remove(): Element to be deleted is mentioned using list name and element.
List = [2.3, 4.445, 3, 5.33, 1.054, 2.5]
print(List.pop())
print(List.pop(0))
del List[0]
print(List)
print(List.remove(3))
2.5
2.3
[4.445, 3, 5.33, 1.054, 2.5]
[4.445, 5.33, 1.054, 2.5]

Tuples
• It is a collection of object much like a list.
• The main different between tuple and list is that tuples are immutable.
• It represent as ( ).
• Values of a tuple are syntactically separated by commas.
• Tuple elements cannot be changes.

Tuples - Create
Tuple1 = () //empty tuple
Tuple2 = ('zooming', 'For’) //tuple with strings
list1 = [1, 2, 4, 5, 6]
Tuple3 = tuple (list1) //tuple with the use of list
Tuple4 = (‘zooming’,) * 3 //tuple with repetition
Tuple5 = (5, 'Welcome', 7, ‘zooming’) //tuple with mixed datatypes

Tuples - Concatenation
• Concatenation of tuple is the process of
joining of two or more Tuples.
• Concatenation is done by the use of ‘+’
operator.
• Concatenation of tuples is done always
from the end of the original tuple.
• Other arithmetic operations do not apply on
Tuples.
# Concatenaton of tuples
Tuple1 = (0, 1, 2, 3)
Tuple2 = (‘Zooming', 'For', ‘stud')
Tuple3 = Tuple1 + Tuple2
print("nTuples after Concatenaton: ")
print(Tuple3
Tuples after Concatenaton:
(0, 1, 2, 3, ‘Zooming', 'For', ‘stud')

Tuples - Slicing
# with Numbers
Tuple1 = tuple(‘ZOOMING')
# From First element
print(Tuple1[1:])
# Reversing the Tuple
print(Tuple1[::-1])
# Printing elements of a Range
print(Tuple1[2:5])
(‘O’,’O’,’M’,’I’,’N’,’G’)
(‘G’,’N’,’I’,’M’,’O’,’O’,’Z’)
(‘O’,’M’,’I’)

Tuples - Deleting
• Tuples are immutable and hence they
do not allow deletion of a part of it.
• Entire tuple gets deleted by the use of
del() method.
• Note- Printing of Tuple after deletion
results to an Error.
# Deleting a Tuple
Tuple1 = (0, 1, 2, 3, 4)
del Tuple1
print(Tuple1)
NameError: name ‘Tuple1’ is not defined

BUILT-IN FUNCTION DESCRIPTION
all() Returns true if all element are true or if tuple is empty
any() return true if any element of the tuple is true. if tuple is empty, return false
len() Returns length of the tuple or size of the tuple
enumerate() Returns enumerate object of tuple
max() return maximum element of given tuple
min() return minimum element of given tuple
sum() Sums up the numbers in the tuple
sorted() input elements in the tuple and return a new sorted list
tuple() Convert an iterable to a tuple.
Tuple – Built-in-Methods

Dictionary
• It is an unordered collection of data values, used to store data values like a map.
• Dictionary holds key:value pair.
• Key value is provided in the dictionary to make it more optimized.
• Each key-value pair in a Dictionary is separated by a colon :,
• whereas each key is separated by a ‘comma’.
• Key – must be unique and immutable datatype.
• Value – can be repeated with any datatype..

Dictionary - Create
# Creating an empty Dictionary
Dict = {}
# Creating a Dictionary with Integer Keys
Dict = {1: 'Zooming', 2: 'For', 3: 'Zooming’}
# Creating a Dictionary with Mixed keys
Dict = {'Name': 'Zooming', 1: [1, 2, 3, 4]}
# Creating a Dictionary with dict() method
Dict = dict({1: 'Zooming', 2: 'For', 3:'Zooming’})
# Creating a Dictionary with each item as a Pair
Dict = dict([(1, 'Zooming'), (2, 'For')])

Dictionary – Adding element
# Creating an empty Dictionary
Dict = {}
# Adding elements one at a time
Dict[0] = 'Zooming'
Dict[2] = 'For'
Dict[3] = 1
# Adding set of values
# to a single Key
Dict['Value_set'] = 2, 3, 4
# Updating existing Key's Value
Dict[2] = 'Welcome’
# Adding Nested Key value to Dictionary
Dict[5] = {'Nested' :{'1' : 'Life', '2' : 'Zooming’}}

Dictionary – Accessing element
# Creating a Dictionary
Dict = {1: 'Zooming', 'name': 'For', 3: 'Zooming'}
# accessing a element using key
print("Acessing a element using key:")
print(Dict['name'])
# accessing a element using key
print("Acessing a element using key:")
print(Dict[1])
# accessing a element using get()
# method
print("Acessing a element using get:")
print(Dict.get(3))

Dictionary – Removing element
Dict = { 5 : 'Welcome', 6 : 'To', 7 : 'Geeks’,
'A' : {1 : 'Geeks', 2 : 'For', 3 : 'Geeks'},
'B' : {1 : 'Geeks', 2 : 'Life'}}
print("Initial Dictionary: ")
print(Dict)
# Deleting a Key value
del Dict[6]
# Deleting a Key from Nested Dictionary
del Dict['A'][2]
# Deleting a Key using pop()
Dict.pop(5)
# Deleting entire Dictionary
Dict.clear()

METHODS DESCRIPTION
copy() They copy() method returns a shallow copy of the dictionary.
clear() The clear() method removes all items from the dictionary.
pop() Removes and returns an element from a dictionary having the given key.
popitem() Removes the arbitrary key-value pair from the dictionary and returns it as tuple.
get() It is a conventional method to access a value for a key.
dictionary_name.values() returns a list of all the values available in a given dictionary.
str() Produces a printable string representation of a dictionary.
update() Adds dictionary dict2’s key-values pairs to dict
setdefault() Set dict[key]=default if key is not already in dict
keys() Returns list of dictionary dict’s keys
items() Returns a list of dict’s (key, value) tuple pairs
has_key() Returns true if key in dictionary dict, false otherwise
fromkeys() Create a new dictionary with keys from seq and values set to value.
type() Returns the type of the passed variable.
cmp() Compares elements of both dict.

Python Variable Types, List, Tuple, Dictionary

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