write the code in python

Sure, let's break down each problem into specific Python scripts.

### Problem 1: Cost Calculation for Premix Concrete Manufacturing
This involves calculating the total cost based on the costs of cement and sand and the required volume of concrete produced.
Here’s a simple Python script:

def calculate_concrete_cost(cement_price_per_litre, sand_price_per_litre, volume_of_concrete):
    # Given ratio of cement to sand (1:1.5)
    litres_cement = volume_of_concrete
    litres_sand = volume_of_concrete * 1.5
    
    # Calculating the cost
    cost_cement = litres_cement * cement_price_per_litre
    cost_sand = litres_sand * sand_price_per_litre
    total_cost = cost_cement + cost_sand
    
    return total_cost

if __name__ == "__main__":
    cement_price_per_litre = float(input("Enter the cost of cement per litre: "))
    sand_price_per_litre = float(input("Enter the cost of sand per litre: "))
    volume_of_concrete = float(input("Enter the volume of premix concrete to be manufactured (in litres): "))

    print(f"The cost of manufacturing the premix concrete is {calculate_concrete_cost(cement_price_per_litre, sand_price_per_litre, volume_of_concrete)}")

### Problem 2: Personal Income Tax Calculator
For this task, you need to prompt for the total income, deductions, and allowances and output the amount of personal income tax due according to a progressive tax scheme.

def calculate_tax(total_income, total_deduction, total_allowance):
    net_income = total_income - total_deduction
    net_chargeable_income = max(0, net_income - total_allowance)

    if net_chargeable_income <= 50_000:
        tax = net_chargeable_income * 0.02
    elif net_chargeable_income <= 100_000:
        tax = 1_000 + (net_chargeable_income - 50_000) * 0.06
    elif net_chargeable_income <= 150_000:
        tax = 4_000 + (net_chargeable_income - 100_000) * 0.1
    elif net_chargeable_income <= 200_000:
        tax = 9_000 + (net_chargeable_income - 150_000) * 0.14
    else:
        tax = 16_000 + (net_chargeable_income - 200_000) * 0.17

    # Apply the cap rule
    capped_tax_rate = 0.15 * net_income
    return min(tax, capped_tax_rate)

if __name__ == "__main__":
    total_income = float(input("Enter your total income: "))
    total_deduction = float(input("Enter your total deductions: "))
    total_allowance = float(input("Enter your total allowance: "))

    print(f"Your personal income tax is {calculate_tax(total_income, total_deduction, total_allowance)}")

### Problem 3: Weighted Average Share Price
Calculate the weighted average price of stock shares over multiple transactions.

def calculate_weighted_average_shares():
    sum_of_products = 0
    sum_of_shares = 0
    while True:
        try:
            shares = int(input("Number of shares (or enter a negative number to stop): "))
            if shares < 0:
                break
            price_per_share = float(input("Price per share: "))
            sum_of_products += shares * price_per_share
            sum_of_shares += shares
        except ValueError:
            print("Please enter a valid numeric input.")
    
    if sum_of_shares > 0:
        return sum_of_products / sum_of_shares
    else:
        return None

if __name__ == "__main__":
    result = calculate_weighted_average_shares()
    if result is not None:
        print(f"The weighted average price per share is {result}")
    else:
        print("No shares entered.")

Ensure these functions are called appropriately within the `if __name__ == "__main__":` block so they only execute when running directly from the command line. This structure keeps the code modular and easily testable.