Variables & Data types

In python variables are containers for storing data values, and data types define the type of data that a variable can hold. Python is dynamically typed, meaning you don't need to declare the type of a variable explicitly - the type is inferred at runtime.

1. Declaring variables

Variables are created by assigning a value using the = operator.

x = 10         # Integer
y = 3.14       # Float
name = "Python" # String
is_active = True # Boolean

2. Naming rules

• Variable names must start with a letter or an underscore(_).
• They can contain letters, numbers, and underscores but cannot start with a number.
• Python is case-sensitive (age and Age are different variables).

3. Data types in python

Data Type	Description	Example
int	Integer numbers	x = 10
float	Floating-point numbers	y = 3.14
str	Strings (text)	name = "Python"
bool	Boolean values (True or False)	is_active = True
list	Ordered, mutable collection	fruits = ["apple", "banana", "cherry"]
tuple	Ordered, immutable collection	coordinates = (10, 20)
dict	Key-value pairs (dictionary)	person = {"name": "John", "age": 25}
set	Unordered, unique items	unique_numbers = {1, 2, 3}
complex	Complex numbers	z = 1 + 2j
NoneType	Represents None (no value)	value = None

4. Type casting

Typecasting in Python refers to the process of converting one data type into another. Python provides built-in functions to perform this conversion explicitly. It is useful when you need to convert data between different types to perform operations or ensure compatibility.

Types of Typecasting

1. Implicit Typecasting

Python automatically converts one data type to another when it is safe to do so, without requiring explicit intervention.

x = 10   # Integer
y = 3.14 # Float
z = x + y  # Python automatically converts `x` to float.
print(z)        # Output: 13.14
print(type(z))  # Output: <class 'float'>

2. Explicit Typecasting

This requires using Python's built-in functions to convert data types manually.

Function	Purpose	Example
int()	Converts to an integer	int("10") → 10
float()	Converts to a floating-point number	float("3.14") → 3.14
str()	Converts to a string	str(10) → "10"
bool()	Converts to a boolean (True/False)	bool(0) → False
list()	Converts to a list	list((1, 2, 3)) → [1, 2, 3]
tuple()	Converts to a tuple	tuple([1, 2, 3]) → (1, 2, 3)
set()	Converts to a set	set([1, 1, 2]) → {1, 2}
dict()	Converts to a dictionary (from key-value pairs)	dict([(1, "a"), (2, "b")]) → {1: "a", 2: "b"}
complex()	Converts to a complex number	complex(1, 2) → 1+2j

5. Operators

Category	Operator	Description	Example
Arithmetic	+	Addition	a + b
	-	Subtraction	a - b
	*	Multiplication	a * b
	/	Division	a / b
	%	Modulus (remainder)	a % b
	**	Exponentiation	a ** b
	//	Floor division	a // b
Relational	==	Equal to	a == b
	!=	Not equal to	a != b
	<	Less than	a < b
	<=	Less than or equal to	a <= b
	>	Greater than	a > b
	>=	Greater than or equal to	a >= b
Logical	and	Logical AND	a > 0 and b > 0
	or	Logical OR	a > 0 or b > 0
	not	Logical NOT	not a
Bitwise	&	Bitwise AND	a & b
	`	`	Bitwise OR
	^	Bitwise XOR	a ^ b
	~	Bitwise NOT	~a
	<<	Left shift	a << 1
	>>	Right shift	a >> 1
Assignment	=	Assign	a = 10
	+=	Add and assign	a += 5
	-=	Subtract and assign	a -= 5
	*=	Multiply and assign	a *= 5
	/=	Divide and assign	a /= 5
	%=	Modulus and assign	a %= 5
	**=	Exponentiation and assign	a **= 5
	//=	Floor division and assign	a //= 5
	&=	Bitwise AND and assign	a &= b
	`	=`	Bitwise OR and assign
	^=	Bitwise XOR and assign	a ^= b
	<<=	Left shift and assign	a <<= 1
	>>=	Right shift and assign	a >>= 1
Membership	in	Returns True if a value is found in a sequence	x in [1, 2, 3]
	not in	Returns True if a value is not in a sequence	x not in [1, 2, 3]
Identity	is	Returns True if both variables refer to the same object	a is b
	is not	Returns True if variables refer to different objects	a is not b
Comparison	<	Less than	a < b
	<=	Less than or equal to	a <= b
	>	Greater than	a > b
	>=	Greater than or equal to	a >= b