Python Programming

Variables in Python: 

-Like C, C++ not declaring the variables with type specification

-Based assigned value type of the variable is assigned by the compiler 

syntax of defining a variables  in python:

my_var = 100 #integer type

my_var = "Best Python tutorial" #string type

my_var = True #boolean type 

Math operation in Python:

type() method is used to return type of the variable 

num1 = 100

num2 = 12.60

type(num1) #Type of this variable; integer

type(num2) #Type of this variable; float

Operators and use  in python 

+  for #addition (3+2 result is 5)

 –  for #subtraction (3-2 result is 1)

 /  for #division (see bit below)

 *  for  #multiplication (2*3 result is 6)

 ** for #raising to a power (2 ** 3 result is 8 (2 to the power of 3 i.e  2*2*2 ))

 %  for #modulo  (Operator returns the reminder after division for example 3%2 result is 1 because reminder is 1)

There is difference between float division and integer division

5 / 2 #float division; result is 2 in Python 2 and 2.5 in Python 3

5 // 2 #integer division; result is 2 in Python 2 and Python 3

math operations priority and order of evaluation in python : 

High priority to raising to a power operator; 

Medium priority to division, multiplication and modulo operators; 

Low priority to addition and subtraction operator;

For example see the below expression evaluation 

result=200 - 4 ** 2 / 4 * 2

print(result) 

output : 192.0

First priority : 4 ** 2 =16, 

second priority : 16/4 =4 then 4*2 = 8, 

thirds priority  200-8 = 192 ; 

result is 192.0

Type conversion between numeric types of data in python:

For type conversion between numeric types of data we are using int() , float() functions to convert int to float vice versa 

int(3.5) #result is 3

float(20) #result is 20.0

Math functions in python:

abs() -> Return the absolute value that is positive value for negative values also it give positive value : 

abs(7) result is 7

print(abs(-5.7)) result is 5.7

max() -> Return the largest values 

max(5, 7) result is 7

min() -> Return the small value

min(5, 7) result is 5

pow()-> Return the power calculated value

pow(2, 3) result is 8 (other way of raising to a power operator)

Boolean and logical operators in python:

Boolean operators return either True  or False for given expression.

and  :  and operator return true if both operands evaluated as true in the expression.

print((3 == 3) and (2 == 2)) returns True.

 3==3 is true ,  2==2 is true 

print((3 == 3) and (3 == 2)) returns False.

 3==3 is true,3 == 2 false 

or: or operator return true if at least one operand evaluated as true in both operands.

print((3 == 3) or (3 == 2)) return True 

3==3 is true,3 == 2 false 

print((4 == 3) or (3 == 2)) return False

4 == 3 is false , 3 == 2 is false 

not : not operator returns the opposite value, if expression evaluated True not operator returns false vice versa

print(not(2 == 3)) returns True True

print(not(3 == 3)) returns False 

bool: bool operator return either True  or False

For following bool operator always return false:

None,False, 0, 0.0,{},(),[], empty string, empty list, empty tuple, empty dictionary etc

print(bool(False)) 

print(bool(None))

print(bool(0))

above result is False 

For following bool operator always return true:

True, 1, 2, string should not empty , list with elements, tuple with elements, dictionary with elements etc

print(bool(True)) 

print(bool(1))

above result is True

List datatype in python:

-List datatype used to store multiple types of data into one variable.

-you can add , delete items if you want .

-List allow duplicates 

-List items accessed based on index , index starts with 0

list1 = ["C", "C++","Python",15,2.15]   #ceating a list 

List functions:

len( )  return the length of the list function that is number of elements in a list

len(list1)  result is 5

list1[0] : return the first element in the list

print(list1[0])  result is CC

list1[0] : return ".NET" : replacing or updating first element in the list

print(list1) : ['.NET', 'C++', 'Python', 15, 2.15]

append(): Append the element to the list in last position.

list1.append("Java") result is ['C', 'C++', 'Python', 15, 2.15, 'Java']

del : deleting the list item based on give index

list1 = ["C", "C++","Python",15,2.15]

del list1[4] result is ['C', 'C++', 'Python', 15]

list1 = ["C", "C++","Python",15,2.15] #list declaration 

pop( ) removing an element from the list based on index

list1.pop(0) return result ['C++', 'Python', 15, 2.15]

remove( ): removing an element from the list based on value not based on index, if list having duplicates only first occurrence  only removed 

list1 = ["C++","Python",15,2.15,"C","C"]

list1.remove("C") result is ['C++', 'Python', 15, 2.15, 'C']

insert( ) : Inserting an element into the specified index.

list1 = ["C++","Python",15,2.15,"C"]

list1.insert(5,".NET") result is ['C++', 'Python', 15, 2.15, 'C', '.NET']

index() : return an index of specified element from the list

list1 = ["C++","Python",15,2.15,"C"]

print(list1.index(2.15)) result is 3

count(): return the no of times element occurrences 

list1 = ["C++","Python",15,2.15,"C",15]

print(list1.count(15)) result is 2

sort()  return the sorted elements list in ascending order , if your applying sort function on list list should contain one type of data otherwise throwing the exception type error.

sorted(list2) return the elements of a list in ascending order and creates a new list at the same time.

sorted(list2, reverse = True): return the elements of a list in descending order and creates a new list at the same time

list2= ["C++","Python",15,2.15,"C",15]

print(list2.sort()) return  TypeError: '<' not supported between instances of 'int' and 'str'

list2= [11,9,10]

list2.sort()

print(list2) result is [9, 10, 11]

list2= ["1","2","0"]

list2.sort()

print(list2) result is ['0', '1', '2']

reverse() : return the elements in reverse order.

list2= [11,9,10]

list2.reverse()

print(list2) resulrt is [10, 9, 11]

Concatenation of two list using + operator 

list1 = ["C++","Python",15,2.15,"C",15]

list2= [11,9,10,7]

print(list1+list2) result is  ['C++', 'Python', 15, 2.15, 'C', 15, 11, 9, 10, 7]

If want repeat the list n no of times use * operator 

list2= [11,9,10,7]

print(list2 * 3) return [11, 9, 10, 7, 11, 9, 10, 7, 11, 9, 10, 7]

min()  return minimum element from the list 

list2= [11,9,10,7]

print(min(list2)) result is 7

max()  return the maximum element from the list from the list

list2= [11,9,10,7]

print(max(list2)) result is 11

extend()  is used to append the list to another list

list1 = ["A","B","C"]

list2= [11,9,10,7]

list1.extend(list2)

print(list1) result is  ['A', 'B', 'C', 11, 9, 10, 7]

Lists - slicing operations:

Slicing mainly mend for getting desired list output from existing list

slic_list1 =["C++","Python",15,2.15,"C","Java","SQL",".NET"]

print(slic_list1[3:]) returns the result [2.15, 'C', 'Java', 'SQL', '.NET']

print(slic_list1[1:5]) returns the result ['Python', 15, 2.15, 'C']

print(slic_list1[:10]) returns the result  ['C++', 'Python', 15, 2.15, 'C', 'Java', 'SQL', '.NET']

print(slic_list1[:]) returns the result ['C++', 'Python', 15, 2.15, 'C', 'Java', 'SQL', '.NET']

print(slic_list1[-1]) returns the result  .NET.NET

print(slic_list1[-2]) returns the result  SQLSQL

print(slic_list1[::2]) returns the result ['C++', 15, 'C', 'SQL']

print(slic_list1[::-1]) returns the result ['.NET', 'SQL', 'Java', 'C', 2.15, 15, 'Python', 'C++']

Sets in Python:

-Sets datatype used to store multiple types of data into one variable.

-Sets not allowing duplicates.

-Like List you can add delete elements from Sets.

-Sets are unordered and unindexed

my_set1 = {"C", 34, True, 40, "Phyton"}

Crating set from list and tuple:

my_list1 = [101, 102, 103, 104, 105, 105, 105, 101]

my_set1 = set(my_list1) # removing the duplicates from the list returning output below

print(my_set1)

output: {101, 102, 103, 104, 105} 

my_string1 = "xxxyyyzzzaaa"

my_set1 = set(my_string1) #removing the duplicates from the string returning output below

print(my_set1)

output : {'y', 'z', 'x', 'a'}

if observe the above from list and string set created as i said above duplicates removed.

Sets functions:

my_set1 = {101, 102, 103, 104, 105}

len( ):  is return the length of the set means number of elements in set 

print(len(my_set1 )) result is 5

add( ) used to add an element to set.

my_set1.add(106)  

print(my_set1 ) result is  {101, 102, 103, 104, 105, 106}

remove( ) :  used to remove an element from set.

my_set1.remove(106)

print(my_set1) result is  {101, 102, 103, 104, 105} 

my_set1 = {"C","C++","Python"}

my_set2={"HTML" , "JavaScript","Jquery","C"}

intersection() This method will return common elements from both the sets 

my_set1 = my_set1.intersection(my_set2)

print(my_set1) return {'C'}

difference() Returns the elements that  first set has and second set doesn't

my_set1 = my_set1.difference(my_set2)

print(my_set1) return output {'C++', 'Python'}

union() 

-returned elements from both the sets. 

-duplicates not allowed 

my_set1 = my_set1.union(my_set2)

print(my_set1) return output {'C++', 'Javascript', 'C', 'Jquery', 'HTML', 'Python'}

pop() Removes a random element from the set because set not having index concept. 

my_set1 = my_set1.pop()

print(my_set1)  return output C

clear(): Clear the set and result is empty set.

my_set1 = my_set1.clear()

print(my_set1) return output None

Frozensets:

-Frozensets are immutable , we can not delete , add an elements to a set

-Frozenset always contain an elements which are there at the time of declaration 

Declaration of Frozenste 

fs1 = frozenset(my_list1) 

type(fs1)

<class 'frozenset'> #the result

fs1.add(10)

AttributeError: 'frozenset' object has no attribute 'add' 

fs1.remove(1)

AttributeError: 'frozenset' object has no attribute 'remove'

fs1.pop()

AttributeError: 'frozenset' object has no attribute 'pop'

fs1.clear()

AttributeError: 'frozenset' object has no attribute 'clear'

 #As we discussed  frozensets are immutable so that we are getting error , if you are trying change anything in set.

What is a strip( ) function?

This function is used to removed space before start and end of the string.

t=" Welcome  "

t.strip() returns "welcome"


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