Python Foundation with Data Structures & Algorithms - Part 02

Python Variables

Variables are containers for storing data values. Variables are nothing but reserved memory locations to store values. This means that when you create a variable you reserve some space in memory.

The interpreter allocates memory and determines what can be stored in the allocated memory depending on the data type of a variable. As a consequence, you can store integers, decimals, or characters in variables by assigning various data types to them.

Every value in Python has a datatype. Different data types in Python are Numbers, List, Tuple, Strings, Dictionary, etc. Variables in Python can be declared by any name or even alphabets like a, aa, abc, etc.

Assigning Values to Variables

 x = 10
 y = "MachineLearning.org.in"
 z = 3.14
 print(x)
 print(y)
 print(z)

10
MachineLearning.org.in
3.14

Variables do not need to be declared with any particular type, and can even change type after they have been set.

 x = 10
 x = "MachineLearning.org.in"
 print(x)

MachineLearning.org.in

Multiple Assignment

 a = b = c = 10
 print(a,b,c)

10 10 10

 a,b,c = 10,3.14,"MachineLearning.org.in"
 print(a)
 print(b)
 print(c)

10
3.14
MachineLearning.org.in

Type Casting

 x = str(3)  
 print(x)

 y = int(3) 
 print(y)

 z = float(3)
 print(z)

3
3
3.0

Get the Type

 x = str(3)  
 print(type(x))

 y = int(3) 
 print(type(y))

 z = float(3)
 print(type(z))

 n = input("Enter any value:")
 print(n)
 print(type(n))

Enter any value:Machine Learning
Machine Learning

 n = int(input("Enter any value:"))
 print(n)
 print(type(n))

Enter any value:10
10

 n = float(input("Enter any value:"))
 print(n)
 print(type(n))

Enter any value:3.14
3.14

 n = str(input("Enter any value:"))
 print(n)
 print(type(n))

Enter any value:Machine Learning
Machine Learning

Concatenation

 x = "Learning"
 print("Machine " + x)

Machine Learning

 x = "Machine "
 y = "Learning "
 z =  x + y
 print(z)

Machine Learning

Python has five standard data types −

Numbers
String
List
Tuple
Dictionary

1. Number

 a = 10
 print(a)

10

delete number

 del a

 print(a)

NameError: name 'a' is not defined

2. String

 s = "MachineLearning.org.in"
 print(s)           # Prints complete string
 print(s[0])        # Prints first character of the string
 print(s[7:15])     # Prints characters starting from 3rd to 5th
 print(s[7:])       # Prints string starting from 3rd character
 print(s * 2)       # Prints string two times
 print('www.' + s)  # Prints concatenated string
 print(s[:])        # Prints complete string with range start to end
 print(s[::])       # Prints complete string with range start to end with increment 1
 print(s[::2])      # Print String with increment of 2
 print(s[-1])       # print last character of a string
 print(s[-3:])      # print last 3 character of a string

MachineLearning.org.in
M
Learning
Learning.org.in
MachineLearning.org.inMachineLearning.org.in
www.MachineLearning.org.in
MachineLearning.org.in
MachineLearning.org.in
Mcieerigogi
n
.in

3. List

      L = [10,3.14,"Machine",45,'Learning',78.98,69,'.org.in']
      print(L)
      print(L[:])
      print(L[::])
      print(L[0])
      print(L[2:5])
      print(L[2:])
      print(L[:5])
      print(L[-1])
      print(L[-3:])

[10, 3.14, 'Machine', 45, 'Learning', 78.98, 69, '.org.in']
[10, 3.14, 'Machine', 45, 'Learning', 78.98, 69, '.org.in']
[10, 3.14, 'Machine', 45, 'Learning', 78.98, 69, '.org.in']
10
['Machine', 45, 'Learning']
['Machine', 45, 'Learning', 78.98, 69, '.org.in']
[10, 3.14, 'Machine', 45, 'Learning']
.org.in
[78.98, 69, '.org.in']

  L1 = [10,20,30]
  L2 = [40,50,60]
  print(L1 + L2)

[10, 20, 30, 40, 50, 60]

  L1 = [10,20,30]
  print(L1 * 3)

[10, 20, 30, 10, 20, 30, 10, 20, 30]

4. Tuples

  T = (10,3.14,"Machine",45,'Learning',78.98,69,'.org.in')
  print(T)
  print(T[:])
  print(T[::])
  print(T[0])
  print(T[2:5])
  print(T[2:])
  print(T[:5])
  print(T[-1])
  print(T[-3:])

(10, 3.14, 'Machine', 45, 'Learning', 78.98, 69, '.org.in')
(10, 3.14, 'Machine', 45, 'Learning', 78.98, 69, '.org.in')
(10, 3.14, 'Machine', 45, 'Learning', 78.98, 69, '.org.in')
10
('Machine', 45, 'Learning')
('Machine', 45, 'Learning', 78.98, 69, '.org.in')
(10, 3.14, 'Machine', 45, 'Learning')
.org.in
(78.98, 69, '.org.in')

  T1 = [10,20,30]
  T2 = [40,50,60]
  print(T1 + T2)

[10, 20, 30, 40, 50, 60]

  T1 = [10,20,30]
  print(T1 * 3)

[10, 20, 30, 10, 20, 30, 10, 20, 30]

5. Dictionary

  d = {}
  print(d)

{}

  d = {'Name':'Kevin','Age':34,'Marks':89.58}
  print(d)
  print(d['Name'])
  print(d['Age'])
  print(d['Marks'])

{'Name': 'Kevin', 'Age': 34, 'Marks': 89.58}
Kevin
34
89.58

  print(d.keys())
  print(d.values())
  print(d.items())

dict_keys(['Name', 'Age', 'Marks'])
dict_values(['Kevin', 34, 89.58])
dict_items([('Name', 'Kevin'), ('Age', 34), ('Marks', 89.58)])