Python Fundamentals

1. Tokens - Smallest Units

Tokens are the smallest individual units in a Python program. The Python interpreter breaks the program into tokens. The five types of tokens are:

2. Keywords

Python has 35 reserved keywords (in Python 3.12) that cannot be used as identifiers.

False, None, True, and, as, assert, async, await, break, class,
continue, def, del, elif, else, except, finally, for, from, global,
if, import, in, is, lambda, nonlocal, not, or, pass, raise,
return, try, while, with, yield

3. Identifiers

Identifiers are names given to program elements like variables, functions, classes, and modules.

Rules for naming identifiers:

• Must start with a letter (a-z, A-Z) or underscore (_).
• Can contain letters, digits, and underscores.
• Cannot start with a digit.
• Cannot be a keyword.
• Case-sensitive (Age, age, and AGE are different).
• No spaces or special symbols except underscore.

Valid: name, _count, student1, total_marks

Invalid: 1st, my-name, class, first name

4. Literals

Literals are constant values that appear directly in a program.

5. Operators

Operators are symbols that perform operations on operands. Python supports: Arithmetic (+, -, *, /, //, %, **), Relational (==, !=, >, <, >=, <=), Logical (and, or, not), Assignment (=, +=, -=, etc.), Bitwise (&, |, ^, ~, <<, >>), Identity (is, is not), and Membership (in, not in) operators.

6. Punctuators

Punctuators are symbols used for grouping and separating code:

() - Parentheses for function calls, tuples, grouping
[] - Square brackets for lists, indexing
{} - Curly braces for dictionaries, sets
, - Comma for separating items
: - Colon for defining blocks, slicing
; - Semicolon for multiple statements on one line

7. Variables in Python

A variable is a named memory location that stores a value. Unlike other languages, Python variables do not need explicit type declaration.

# Variable assignment
name = "Riya"
age = 17
marks = 95.5
is_student = True

# Multiple assignment
x = y = z = 10
a, b, c = 1, 2, 3

8. Data Types

Use type() function to check the data type of a variable: print(type(x)).

9. Mutable and Immutable Types

10. Type Conversion

Implicit conversion: Python automatically converts one data type to another when needed.

x = 10    # int
y = 3.5   # float
z = x + y # z will be float (13.5) - implicit conversion

Explicit conversion: Programmer manually converts using functions.

a = "10"
b = int(a)     # Explicit conversion: string to int
c = float(b)   # int to float
d = str(c)     # float to string

11. Input and Output

Output: The print() function displays output.

print("Hello, World!")
print("Value:", 10)
print("Sum of", 5, "and", 3, "is", 8)

Input: The input() function reads input as a string.

name = input("Enter your name: ")
age = int(input("Enter your age: "))  # Convert to int
height = float(input("Enter height: "))  # Convert to float

12. Output Formatting

# Using f-strings (Python 3.6+)
name = "Riya"
marks = 95.5
print(f"Student: {name}, Marks: {marks}")

# Using format() method
print("Student: {}, Marks: {}".format(name, marks))

# Using % formatting
print("Student: %s, Marks: %.1f" % (name, marks))

13. Dynamic Typing

Python is dynamically typed, meaning a variable can change its type during program execution.

x = 10        # x is int
print(type(x))  # 
x = "Hello"   # x is now str
print(type(x))  # 
x = 3.14      # x is now float
print(type(x))  #