How to make the value that goes to 0, to make it to go back to same value in python?

Question

I'm using Python PIL module to draw some lines and I use for loop to change the width of the line. But now I would like to do, when line width is to 0, I want to go and add value of lw. Basicly when width value go to zero, then I want it to go back to the 120.

This is my code...

from PIL import Image, ImageDraw

img = Image.new('RGB', (2000, 2000), (0, 0, 0))
draw = ImageDraw.Draw(img)

lw = 0
for y in range(-100, 2100, 100):
    lw = lw + 10
    draw.line((2000, y, 0, y), (255,0,0), 120-lw)   
img 

This is an image from this code...

I was thinking to use if statement but I don't know where to incorporate it. Any ideas?

Thanks in advance!

Answer 1

for y in range(-100, 2100, 100):
    lw = lw + 10
    draw.line((2000, y, 0, y), (255,0,0), 120-lw)   

Nice attempt.

---

I was thinking to use if statement but I don't know where to incorporate it. Any ideas?

In this case I would suggest to do this:

for y in range(-100, 2100, 100):
    lw = lw + 10
    if (lw >= 120): # When lw reaches 120...
        lw = 0 # ...you set it to 0
    draw.line((2000, y, 0, y), (255,0,0), 120-lw)

---

Anyway a more elegant solution (which doesn't involve if statements) would be this:

for y in range(-100, 2100, 100):
    lw = lw + 10
    draw.line((2000, y, 0, y), (255,0,0), 120-(lw%120))

The % operator gets the remainder of lw/120, so that when lw>=120 you won't have a value greater than 120 anyway.

EDIT

---

I want to go from 120 to 0, and from 0 to 120. In this way it goes like this (120, 110,..., 20, 10, 0, 120, 110,...), but I would like to go like this (120, 110,..., 20, 10, 0, 10, 20,...,

In this case you have to use an if statement:

incrementing = True
lw = 0
for y in range(-100, 2100, 100):
    if (lw == 120):
        incrementing = False
    elif (lw == 0):
        incrementing = True
    if (incrementing):
        lw = lw + 10
    else:
        lw = lw - 10
    draw.line((2000, y, 0, y), (255,0,0), 120-lw)   

My suggestion is to use a boolean variable to make the incrementing/decrementing easier.