Numbers: int, float and converting text

Models are paid for by the amount of text they read and write, so even a program about text does sums. Here is the arithmetic, and the mistake everyone makes.

price = 499
quantity = 2
print(price * quantity)
print(10 / 4)
print(10 // 4)
print(10 % 4)

* multiplies. / always gives a float, even when the answer is whole. // divides and drops the part after the decimal point, and % gives what is left over.

A cost estimate

Model providers count text in tokens, pieces of words, and charge a price per thousand or per million of them.

tokens = 1234
price_per_1000 = 0.15
cost = tokens / 1000 * price_per_1000
print(cost)
print(round(cost, 2))

round(cost, 2) keeps two digits after the point, so 0.1851 becomes 0.19. Round a cost before showing it to a person; nobody is billed in ten-thousandths.

Text that looks like a number

A number that arrives from a file, a form or a model often arrives as text. Adding to it fails.

quantity = "2"
print(quantity + 1)

The quotes made quantity a string, and Python will not guess whether you meant maths or joining text. Convert it first.

quantity = "2"
print(int(quantity) + 1)
print(float("0.15") * 2)
print("Total: " + str(998))

int, float and str each turn a value into that type. Text that is not a number cannot become one, and that is a different error:

print(int("two"))