Python -- Ancient Taxation

Question

In this problem it says that the first 10,000 drachs are not taxed, the next 20,000 are taxed 10%, the next 40,000 are taxed 20%, and any after the first 70,000 are taxed 30%. I'm fairly new to python, but this is what i have so far. I'm not sure where i've gone wrong. I think it is because i haven't defined the "tax" variable, but i'm not sure. any help would be much appreciated. THANKS!

**The code must also be terminated if the user enters in a negative number and i'm not sure how to add this to my for loops.

def income(drach):

    for drach in range(10000):
        tax = 0
    for drach in range(10000 , 30000):
        tax = ((drach - 10000)*0.1)
    for drach in range(30000 , 70000):
        tax = ((drach - 30000)*0.2) + 2000
    for drach in range(70000 , 10**999):
        tax = ((drach - 70000)*0.3) + 10000

    print tax

Answer 1

I think this is the correct taxation schema:

   def tax(income):
        tax=0;
        if income > 70000 : 
            tax += (income-70000)* 0.3 
            income = 70000
        if income > 30000 : 
            tax += (income-30000)* 0.2
            income = 30000
        if income > 10000 : 
            tax += (income-10000)* 0.1
        return tax;

Answer 2

The keyword for is used for looping over iterables. For example

for drach in range(10000):
    tax = 0

assigns every value in the range 0, 1, 2, ..., 9998, 9999 to drach, and executes tax = 0 for each of these. This almost certainly isn't what you want -- you probably want if instead of for.

You could use the max() function to avoid using if as well:

tax = max(drach - 10000, 0) * 0.1 + 
      max(drach - 30000, 0) * 0.1 +
      max(drach - 70000, 0) * 0.1

Answer 3

You most likely don't want to use for in construct. In a for x in iterable construct, you loop through iterable assigning x to the next element yielded by iterable, until you reach the end (i.e. a StopIteration is raised).

Instead, you probably want to preserve the parameter drach and apply it to the taxation conditions.

As Sven Marnach pointed out:

The check drach in range(10000 , 30000) is very inefficient in Python 2. Better use 10000 <= drach < 30000.

So:

def income(drach):
    tax = 0
    if 10000 <= drach <= 30000:
        tax += ((drach - 10000)*0.1)
    if 30000 <= drach <= 70000:
        tax += ((drach - 30000)*0.2) + 2000
    if drach > 70000:
        tax += ((drach - 70000)*0.3) + 10000

    return tax

As an alternative you could loop through the slices:

def income(drach):
    tax = 0
    percent = step = 0.1
    lower = 10000
    for upper in [30000, 70000]:
        if lower < drach <= upper:
            tax += (drach - lower) * percent
        lower = upper
        percentage += step
    if lower < drach:
        tax += (drach - lower) * percent
    return tax