Data Types and Variables

# Python Basics: Data Types, Variables, and Collections

# =============================================================================
# VARIABLE SCOPE
# =============================================================================

# Global scope - accessible everywhere in the file
global_var = "I'm global!"

def demonstrate_scope():
    # Local scope - only accessible inside this function
    local_var = "I'm local!"
    print(f"Inside function: {global_var}")  # Can access global
    print(f"Inside function: {local_var}")   # Can access local
    
    # Modifying global variables requires 'global' keyword
    global global_var
    global_var = "I've been changed!"

demonstrate_scope()
print(f"Outside function: {global_var}")    # Shows the changed value
# print(local_var)  # This would cause an error - local_var doesn't exist here

# =============================================================================
# DATA TYPES: int, float, str
# =============================================================================

# Creating different types
my_int = 42
my_float = 3.14
my_string = "Hello World"

print(f"Integer: {my_int}, type: {type(my_int)}")
print(f"Float: {my_float}, type: {type(my_float)}")
print(f"String: {my_string}, type: {type(my_string)}")

# TYPE CONVERSION (Casting)
print("\n--- Type Conversion ---")

# Converting to int
str_number = "123"
converted_int = int(str_number)
print(f"String '123' to int: {converted_int}")

float_number = 45.67
converted_int_from_float = int(float_number)  # Truncates decimal
print(f"Float 45.67 to int: {converted_int_from_float}")

# Converting to float
int_to_float = float(my_int)
str_to_float = float("98.5")
print(f"Int 42 to float: {int_to_float}")
print(f"String '98.5' to float: {str_to_float}")

# Converting to string
int_to_str = str(my_int)
float_to_str = str(my_float)
print(f"Int 42 to string: '{int_to_str}'")
print(f"Float 3.14 to string: '{float_to_str}'")

# =============================================================================
# BOOLEAN AND NONE
# =============================================================================

print("\n--- Boolean and None ---")

# Boolean values
is_sunny = True
is_raining = False
print(f"Is sunny: {is_sunny}")
print(f"Is raining: {is_raining}")

# Boolean conversion
print(f"bool(1): {bool(1)}")        # True
print(f"bool(0): {bool(0)}")        # False
print(f"bool('text'): {bool('text')}")  # True (non-empty string)
print(f"bool(''): {bool('')}")      # False (empty string)
print(f"bool([1,2,3]): {bool([1,2,3])}")  # True (non-empty list)
print(f"bool([]): {bool([])}")      # False (empty list)

# None type
my_none = None
print(f"None value: {my_none}")
print(f"None type: {type(my_none)}")
print(f"Is None falsy? {bool(my_none)}")  # False

# =============================================================================
# RANGE FUNCTION
# =============================================================================

print("\n--- Range Function ---")

# Basic range - range(stop)
print("range(5):", list(range(5)))  # [0, 1, 2, 3, 4]

# Range with start and stop - range(start, stop)
print("range(2, 8):", list(range(2, 8)))  # [2, 3, 4, 5, 6, 7]

# Range with start, stop, and step - range(start, stop, step)
print("range(0, 10, 2):", list(range(0, 10, 2)))  # [0, 2, 4, 6, 8]
print("range(10, 0, -1):", list(range(10, 0, -1)))  # [10, 9, 8, 7, 6, 5, 4, 3, 2, 1]

# Common use in loops
print("Using range in a loop:")
for i in range(3):
    print(f"  Loop iteration: {i}")

# =============================================================================
# COLLECTIONS
# =============================================================================

print("\n--- Collections ---")

# LIST - Ordered, mutable, allows duplicates
print("LISTS:")
my_list = [1, 2, 3, "hello", True]
print(f"List: {my_list}")
print(f"First item: {my_list[0]}")
print(f"Last item: {my_list[-1]}")

# List methods
my_list.append("new item")
print(f"After append: {my_list}")
my_list.remove(2)
print(f"After removing 2: {my_list}")

# TUPLE - Ordered, immutable, allows duplicates
print("\nTUPLES:")
my_tuple = (1, 2, 3, "hello", True)
print(f"Tuple: {my_tuple}")
print(f"First item: {my_tuple[0]}")
# my_tuple[0] = 5  # This would cause an error - tuples are immutable

# Tuple unpacking
coordinates = (10, 20)
x, y = coordinates
print(f"Unpacked coordinates: x={x}, y={y}")

# DICTIONARY - Key-value pairs, unordered, mutable
print("\nDICTIONARIES:")
my_dict = {
    "name": "Alice",
    "age": 30,
    "city": "New York",
    "is_student": False
}
print(f"Dictionary: {my_dict}")
print(f"Name: {my_dict['name']}")
print(f"Age: {my_dict.get('age')}")  # Safer way to access

# Adding/modifying dictionary items
my_dict["email"] = "alice@email.com"
my_dict["age"] = 31
print(f"Updated dictionary: {my_dict}")

# Dictionary methods
print(f"Keys: {list(my_dict.keys())}")
print(f"Values: {list(my_dict.values())}")
print(f"Items: {list(my_dict.items())}")

# SET - Unordered, mutable, no duplicates
print("\nSETS:")
my_set = {1, 2, 3, 3, 4, 4, 5}  # Duplicates will be removed
print(f"Set: {my_set}")

# Set operations
my_set.add(6)
print(f"After adding 6: {my_set}")
my_set.remove(2)
print(f"After removing 2: {my_set}")

# Set operations with other sets
other_set = {4, 5, 6, 7, 8}
print(f"Union: {my_set | other_set}")
print(f"Intersection: {my_set & other_set}")
print(f"Difference: {my_set - other_set}")

# =============================================================================
# PRACTICAL EXAMPLES
# =============================================================================

print("\n--- Practical Examples ---")

# Example 1: Type checking and conversion
def safe_divide(a, b):
    """Safely divide two numbers with type checking"""
    try:
        # Convert to float to handle both int and float inputs
        num1 = float(a)
        num2 = float(b)
        
        if num2 == 0:
            return None  # Return None for division by zero
        
        return num1 / num2
    except (ValueError, TypeError):
        return None  # Return None if conversion fails

print(f"safe_divide('10', '2'): {safe_divide('10', '2')}")
print(f"safe_divide(15, 3): {safe_divide(15, 3)}")
print(f"safe_divide(10, 0): {safe_divide(10, 0)}")

# Example 2: Working with collections
def analyze_grades(grades):
    """Analyze a list of grades and return statistics"""
    if not grades:  # Check if list is empty
        return None
    
    # Convert all grades to float and remove duplicates
    unique_grades = set(float(grade) for grade in grades)
    grade_list = list(unique_grades)
    
    stats = {
        "count": len(grade_list),
        "highest": max(grade_list),
        "lowest": min(grade_list),
        "average": sum(grade_list) / len(grade_list)
    }
    
    return stats

sample_grades = [85, 92, 78, 92, 88, 95, 85, 90]
result = analyze_grades(sample_grades)
print(f"Grade analysis: {result}")

# Example 3: Using range with different step values
print("\nCreating different number sequences:")
print("Even numbers 0-10:", list(range(0, 11, 2)))
print("Odd numbers 1-10:", list(range(1, 11, 2)))
print("Countdown from 10:", list(range(10, 0, -1)))
print("Every 3rd number from 0-30:", list(range(0, 31, 3)))