David Tan David Tan - 3 months ago 13
Python Question

Programmatically generate if elif elif elif else

I would like to condense some wet code that looks like this:

if slips[i] < 3000:
ac.setBackgroundColor(wheel['slip'], 0, 0, 0)
# setBackgroundOpacity deliberately omitted here
elif slips[i] < 3700:
ac.setBackgroundColor(wheel['slip'], .2, .4, .2)
ac.setBackgroundOpacity(wheel['slip'], 1)
elif slips[i] < 4100:
ac.setBackgroundColor(wheel['slip'], 0, 1, 0)
ac.setBackgroundOpacity(wheel['slip'], 1)
elif slips[i] < 4500:
ac.setBackgroundColor(wheel['slip'], 0, 0, 1)
ac.setBackgroundOpacity(wheel['slip'], 1)
else:
ac.setBackgroundColor(wheel['slip'], 1, 0, 0)
ac.setBackgroundOpacity(wheel['slip'], 1)


Each time this snippet of code is repeated, the only things that change are the background canvas (
wheel['slip']
in this case), and the numbers in the if elif else's.

My first thought to dry this up was to make something that could be used like this:

if_replacer(wheel['slip'], slips[i], 3000, 3700, 4100, 4500)

def if_replacer(canvas, value, *args):
# idunno


My question is, how would I programmatically generate the if elif else's? I know I could hard-code it like so:

def if_replacer(canvas, value, c1, c2, c3, c4):
if value < c1:
ac.setBackgroundColor(canvas, 0, 0, 0)
return
elif value < c2:
ac.setBackgroundColor(canvas, .2, .4, .2)
elif value < c3:
ac.setBackgroundColor(canvas, 0, 1, 0)
elif value < c4:
ac.setBackgroundColor(canvas, 0, 0, 1)
else:
ac.setBackgroundColor(canvas, 1, 0, 0)
ac.setBackgroundOpacity(canvas, 1)


But I'm interested if there is a succinct and Pythonic method to accomplish this.

Answer

Here's one possible solution.

def least_bound_index(value, bounds):
    """return the least index such that value < bounds[i], or else len(bounds)""" 
    for i, b in enumerate(bounds):
        if value < b:
            return i
    return i+1

bounds = [3000, 3700, 4100, 4500]
bgcolors = [(0, 0, 0), (.2, .4, .2), (0, 1, 0), (0, 0, 1), (1, 0, 0)]

i = least_bound_index(slips[i], bounds)
ac.setBackgroundColor(wheel['slip'], *bgcolors[i])
if i > 0:
    ac.setBackgroundOpacity(wheel['slip'], 1)