Python Variables, Data Types, and Operators – A Complete Guide for Students

# Creating variables
name = "Aarav"
age = 15
height = 5.6
is_student = True

# Using variables
print(name)        # Output: Aarav
print(age)         # Output: 15
print(height)      # Output: 5.6
print(is_student)  # Output: True

# Valid variable names
student_name = "Priya"
_score = 95
totalMarks2 = 500

# Invalid variable names (these will cause errors)
# 2name = "Raj"       # Cannot start with a digit
# my name = "Raj"     # Cannot have spaces
# for = 10            # Cannot use keywords

roll_number = 42
temperature = -5
zero = 0

print(type(roll_number))  # Output: <class 'int'>

percentage = 87.5
pi = 3.14159
price = 49.99

print(type(percentage))  # Output: <class 'float'>

school = "Delhi Public School"
greeting = 'Hello, World!'

# String concatenation (joining strings)
first_name = "Ananya"
last_name = "Sharma"
full_name = first_name + " " + last_name
print(full_name)  # Output: Ananya Sharma

# String repetition
line = "-" * 30
print(line)  # Output: ------------------------------

# String length
print(len(school))  # Output: 18

is_passed = True
has_submitted = False

print(10 > 5)    # Output: True
print(3 == 7)    # Output: False
print(type(is_passed))  # Output: <class 'bool'>

subjects = ["Maths", "Physics", "Chemistry", "Computer Science"]
marks = [92, 88, 76, 95]
mixed = ["Aarav", 15, True, 5.6]

# Accessing items (index starts from 0)
print(subjects[0])    # Output: Maths
print(subjects[2])    # Output: Chemistry

# Changing an item
subjects[1] = "Biology"
print(subjects)  # Output: ['Maths', 'Biology', 'Chemistry', 'Computer Science']

# Adding an item
subjects.append("English")
print(len(subjects))  # Output: 5

coordinates = (28.6139, 77.2090)  # Delhi coordinates
days = ("Monday", "Tuesday", "Wednesday")

print(coordinates[0])  # Output: 28.6139
print(len(days))       # Output: 3

# This will cause an error because tuples are immutable:
# days[0] = "Sunday"   # TypeError!

student = {
    "name": "Riya Patel",
    "class": 11,
    "school": "St. Xavier's",
    "percentage": 91.5
}

print(student["name"])        # Output: Riya Patel
print(student["percentage"])  # Output: 91.5

# Adding a new key-value pair
student["city"] = "Mumbai"
print(student.keys())

# String to Integer
age_text = "16"
age_number = int(age_text)
print(age_number + 1)  # Output: 17

# Integer to Float
whole = 10
decimal = float(whole)
print(decimal)  # Output: 10.0

# Number to String
score = 95
message = "Your score is " + str(score)
print(message)  # Output: Your score is 95

# Float to Integer (removes decimal, does not round)
print(int(7.9))   # Output: 7
print(int(3.2))   # Output: 3

# Getting text input
name = input("Enter your name: ")
print("Hello, " + name + "!")

# Getting numeric input
age = int(input("Enter your age: "))
print("Next year you will be", age + 1)

# Getting decimal input
height = float(input("Enter your height in feet: "))
print("Your height is", height, "feet")

a = 17
b = 5

print(a + b)    # Addition:         22
print(a - b)    # Subtraction:      12
print(a * b)    # Multiplication:   85
print(a / b)    # Division:         3.4   (always returns float)
print(a // b)   # Floor Division:   3     (removes decimal part)
print(a % b)    # Modulus:          2     (remainder)
print(a ** b)   # Exponent:         1419857  (17 to the power 5)

x = 10
y = 20

print(x == y)   # Equal to:                False
print(x != y)   # Not equal to:            True
print(x > y)    # Greater than:            False
print(x < y)    # Less than:               True
print(x >= 10)  # Greater than or equal:   True
print(x <= 5)   # Less than or equal:      False

age = 16
has_id = True

# and: Both conditions must be True
print(age >= 16 and has_id)     # True

# or: At least one condition must be True
print(age >= 18 or has_id)      # True

# not: Reverses the result
print(not has_id)               # False

# Combining conditions
marks = 85
attendance = 90
print(marks > 75 and attendance > 80)  # True

score = 100

score += 10   # Same as: score = score + 10  -> 110
score -= 20   # Same as: score = score - 20  -> 90
score *= 2    # Same as: score = score * 2   -> 180
score //= 3   # Same as: score = score // 3  -> 60
score %= 7    # Same as: score = score % 7   -> 4

print(score)  # Output: 4

# Student Report Card Calculator
print("=" * 40)
print("   STUDENT REPORT CARD GENERATOR")
print("=" * 40)

name = input("Enter student name: ")
roll = int(input("Enter roll number: "))

print("\nEnter marks for each subject (out of 100):")
english = float(input("English: "))
maths = float(input("Mathematics: "))
science = float(input("Science: "))
computer = float(input("Computer Science: "))
hindi = float(input("Hindi: "))

total = english + maths + science + computer + hindi
average = total / 5

if average >= 90:
    grade = "A+"
elif average >= 75:
    grade = "A"
elif average >= 60:
    grade = "B"
else:
    grade = "C"

all_passed = english >= 33 and maths >= 33 and science >= 33 and computer >= 33 and hindi >= 33

print("\n" + "=" * 40)
print("         REPORT CARD")
print("=" * 40)
print("Name:       ", name)
print("Roll No:    ", roll)
print("-" * 40)
print("Total:      ", str(total) + "/500")
print("Average:    ", round(average, 2))
print("Grade:      ", grade)
print("Status:     ", "PASSED" if all_passed else "FAILED")
print("=" * 40)