Untitled

'''
    This is a function to perform calculations (addition, subtraction, 
    multiplication and division)
    It accepts three parameters: a, b, op.
        a: first number
        b: second number
        op: type of operation
    In case of division by zero it raises an error.
    The function returns a number or None

'''

def calc(a, b , op):
    # If add operation we sum the elements
    if op == 'add':
        return a + b
    # If sub operation we subtract the elements
    elif op == 'sub':
        return a - b
    # If mul operation we multiply the elements
    elif op == 'mul':
        return a * b
    # If div operation we divide the elements
    elif op == 'div':
        # If dividing by zero we raise an error
        if b == 0:
            raise ValueError("Division by zero")
        # Otherwise we return the result
        return a / b
    else:
        # If we don't provide an operation we return None
        return None
    

# Examples
     
print(calc(4, 3, "add"))    # 7
print(calc(4, 3, "sub"))    # 1
print(calc(4, 3, "mult"))   # 12
print(calc(4, 3, "div"))    # 1.33333
print(calc(4, 3, ""))       # None