Basics of Python

Variables

• Variables are containers for storing the data values, with which we can further reference and manipulate the values.
• Literals are values used in Python. Types are:

Data Type	Value	Description
Numeric	Integer	Whole numbers
	Float	Decimal number
	Complex	Contains real and imaginary part
Boolean	True	Represents the truth value
	False	Represents the false value
Collection	List	Ordered and changeable collection
	Tuples	Ordered and unchangeable collection
	Dictionary	Unordered, changeable and indexed collection
	Sets	Unordered and unindexed collection
String	Sequence of Characters	A sequence of Unicode characters
Special	None	Represents the absence of value
	Not a Number (NaN)	Represents a numeric value that is undefined or unrepresentable

Operators in Python

Operator Type	Operator	Description
Arithmetic Operators	Addition: +	Adds values on either side of the operator
	Subtraction: -	Subtracts right hand operand from left hand operand
	Multiplication: *	Multiplies values on either side of the operator
	Division: /	Divides left hand operand by right hand operand
	Modulus: %	Divides left hand operand by right hand operand and returns the remainder
	Exponentiation: **	Performs exponential (power) calculation on operators
	Floor Division: //	The division of operands where the result is the quotient in which the digits after the decimal point are removed
Comparison Operators	Equal to: ==	Returns True if both operands are equal
	Not equal to: !=	Returns True if operands are not equal
	Greater than: >	Returns True if left operand is greater than the right one
	Less than: <	Returns True if left operand is less than the right one
	Greater than or equal to: >=	Returns True if left operand is greater than or equal to the right one
	Less than or equal to: <=	Returns True if left operand is less than or equal to the right one
Assignment Operators	Assign: =	Assigns values from right side operands to left side operand
	Add and assign: +=	It adds right operand to the left operand and assign the result to left operand
	Subtract and assign: -=	It subtracts right operand from the left operand and assign the result to left operand
	Multiply and assign: *=	It multiplies right operand with the left operand and assign the result to left operand
	Divide and assign: /=	It divides left operand with the right operand and assign the result to left operand
	Modulus and assign: %=	It takes modulus using two operands and assign the result to left operand
	Floor division and assign: //=	It performs floor division on operators and assign value to the left operand
	Exponent and assign: **=	Performs exponent calculation on operators and assign value to the left operand
Logical Operators	Logical AND: and	Returns True if both the operands are true
	Logical OR: or	Returns True if either of the operands is true
	Logical NOT: not	Returns True if operand is false (complements the operand)
Bitwise Operators	Bitwise AND: &	Performs bitwise AND operation
	Bitwise OR: |	Performs bitwise OR operation
	Bitwise NOT: ~	Inverts all the bits
	Bitwise XOR: ^	Performs bitwise exclusive OR operation
	Bitwise right shift: >>	Shift right by pushing copies of the leftmost bit on the left, and let the rightmost bits fall off
	Bitwise left shift: <<	Shift left by pushing zeros in from the right and let the leftmost bits fall off
Identity Operators	is	Returns True if both variables are the same object
	is not	Returns True if both variables are not the same object
Membership Operators	in	Returns True if a sequence with the specified value is present in the object
	not in	Returns True if a sequence with the specified value is not present in the object

Collection Object - Strings:

Common Operations:

1. Concatenation

    x = "Hello"
    y = " Python"
    print(x+y)
   

2. Repetition

    x = "Hello "
    print(x*2)
   

3. Membership Operators

    x = "hello python"
    if "hello" in x:
        print(True)
    else:
        print(False)
   

4. Length

    x = "hello python"
    print(len(x))
   

5. Indexing

    x = "hello python"
    print(x[0])
    print(x[6])
   

6. Slicing

    x = "hello python"
    x[1:7]
   

Builtin Functions

Function	Description
strip()	Returns a copy of the string with both leading and trailing characters removed
lower()	Converts all uppercase characters in a string into lowercase characters and returns it
upper()	Converts all lowercase characters in a string into uppercase characters and returns it
len()	Returns the number of items in an object
type()	Returns the type of an object
print()	Prints the specified message to the screen
input()	Reads a line from input, converts it to a string and returns it
int()	Converts a specified value into an integer
str()	Converts a specified value into a string
float()	Converts a specified value into a floating point number
list()	Converts a specified value into a list
dict()	Converts a specified value into a dictionary
set()	Converts a specified value into a set
sorted()	Returns a sorted list from the specified iterable
range()	Returns a sequence of numbers, starting from 0 by default, and increments by 1 (also default), and stops before a specified number
sum()	Returns the sum of all items in an iterable
max()	Returns the item with the highest value in an iterable
min()	Returns the item with the lowest value in an iterable

Data Types in Python

Python has several built-in data types that can be categorized as follows:

1. Numeric Types

Data Type	Description	Example
int	Integer numbers (positive or negative whole numbers)	x = 42, y = -10
float	Floating-point numbers (decimal numbers)	pi = 3.14159, temp = -2.5
complex	Complex numbers with real and imaginary parts	z = 3 + 4j, real: 3, imag: 4

2. Boolean Type

Data Type	Description	Example
bool	Boolean values representing truth values	is_valid = True, has_error = False

3. Sequence Types

Data Type	Description	Example
list	Ordered, mutable collection that allows duplicate members	fruits = ["apple", "banana", "cherry"]
tuple	Ordered, immutable collection that allows duplicate members	point = (10, 20), colors = ("red", "green", "blue")
range	Sequence of numbers, typically used in loops	numbers = range(5) → [0, 1, 2, 3, 4]

4. Text Type

Data Type	Description	Example
str	String of Unicode characters (text)	name = "Python", message = 'Hello World'

5. Set Types

Data Type	Description	Example
set	Unordered collection with no duplicate elements	vowels = {'a', 'e', 'i', 'o', 'u'}
frozenset	Immutable version of a set	constants = frozenset([3.14, 2.71])

6. Mapping Type

Data Type	Description	Example
dict	Unordered collection of key-value pairs	person = {"name": "John", "age": 30}

7. Binary Types

Data Type	Description	Example
bytes	Immutable sequence of bytes	data = b'Hello'
bytearray	Mutable sequence of bytes	data = bytearray(5)
memoryview	Object that exposes the memory buffer interface	mem = memoryview(bytes(5))

8. Special Type

Data Type	Description	Example
NoneType	Represents the absence of a value (null)	result = None, empty_list = []

Quick Reference Examples

# Numeric types
age = 25          # int
price = 19.99     # float
complex_num = 2+3j # complex

# Boolean
is_active = True

# Sequence types
items = [1, 2, 3]        # list
coordinates = (10, 20)   # tuple
numbers = range(5)       # range: 0,1,2,3,4

# Text
greeting = "Hello"

# Sets
unique_colors = {"red", "green", "blue"}

# Dictionary
student = {"name": "Alice", "grade": 85}

# Binary
data = b"test"
buffer = bytearray(10)

# None
result = None

List Comprehension

• List comprehension is a concise and expressive way to create lists in python.
• It provides a more compact syntax for creating lists by specifying the elements of the list and the conditions under which they should be included.
• Sytax:
  • new_list = [expression for item in iterable if condition ]

• Example:

    x = [1, 2, 3, 4, 5, 6, 7, 8]
  
    result = []
    for i in x:
        result.append(i**2)
    print(result)
  

• Using List Comprehension

    x = [1, 2, 3, 4, 5, 6, 7, 8]
    result = [i**2 for i in x]
    print(result)
  

  OR

    x = [1, 2, 3, 4, 5, 6, 7, 8]
    result = [i**2 for i in x if i%2==0]
    print(result)
  

Buit-in Functions - Lists

Function	Description
append()	Adds an element at the end of the list
clear()	Removes all the elements from the list
copy()	Returns a copy of the list
count()	Returns the number of elements with the specified value
extend()	Add the elements of a list (or any iterable), to the end of the current list
index()	Returns the index of the first element with the specified value
insert()	Adds an element at the specified position
pop()	Removes the element at the specified position
remove()	Removes the item with the specified value
reverse()	Reverses the order of the list
sort()	Sorts the list

Buit-in Functions - Tuples

Function	Description
count()	Returns the number of times a specified value occurs in a tuple
index()	Searches the tuple for a specified value and returns the position of where it was found

Buit-in Functions - Sets

Function	Description
add()	Adds an element to the set
clear()	Removes all the elements from the set
copy()	Returns a copy of the set
difference()	Returns a set containing the difference between two or more sets
difference_update()	Removes the items in this set that are also included in another, specified set
discard()	Remove the specified item
intersection()	Returns a set, that is the intersection of two other sets
intersection_update()	Removes the items in this set that are not present in other, specified set(s)
isdisjoint()	Returns whether two sets have a intersection or not
issubset()	Returns whether another set contains this set or not
issuperset()	Returns whether this set contains another set or not
pop()	Removes an element from the set
remove()	Removes the specified element
symmetric_difference()	Returns a set with the symmetric differences of two sets
symmetric_difference_update()	inserts the symmetric differences from this set and another
union()	Return a set containing the union of sets
update()	Update the set with the union of this set and others

Buit-in Functions - Dictionary

Function	Description
clear()	Removes all the elements from the dictionary
copy()	Returns a copy of the dictionary
fromkeys()	Returns a dictionary with the specified keys and value
get()	Returns the value of the specified key
items()	Returns a list containing a tuple for each key value pair
keys()	Returns a list containing the dictionary’s keys
pop()	Removes the element with the specified key
popitem()	Removes the last inserted key-value pair
setdefault()	Returns the value of the specified key. If the key does not exist: insert the key, with the specified value
update()	Updates the dictionary with the specified key-value pairs
values()	Returns a list of all the values in the dictionary