Python - Ensuring a variable holds a positive number

Question

I am looking for an elegant way to ensure that a given variable remains positive.

I have two variables that hold positive float numbers and I decrement them according to certain conditions. At the end I want to guarantee that I still have positive numbers (or 0 at most). The pseudo code looks something like this:

list = [...]

value1 = N
value2 = M

for element in list:
    if ... :
        value1 -= X
    if ... :
        value2 -= Y

Is there a more elegant solution than just adding two ifs at the end?

Answer 1

I am unclear as to what you want to do -- either the variables can be negative, or they can't.

• If you are decrementing a variable repeatedly and after doing so you want to check whether they are negative, do so with an if -- that's what it's for!

  if value < 0: # do stuff
  

• If you think the variables should never be negative and you want to assert this fact in the code in the code, you do

  assert value > 0
  

  which may raise an AssertionError if the condition doesn't hold (assert will not execute when Python is not run in debug mode).

• If you want the variable to be 0 if it has been decreased below 0, do

  value = max(value, 0)
  

• If you want the variable to be negated if it is negative, do

  value = value if value > 0 else -value
  

  or

  value = abs(value)