Wrong syntax error in list comprehension with Python

Question

I'm getting SyntaxError: invalid syntax on the following list comprehension:

colors = [(141, 0, 248, 0.4) if x >= 150 and x < 200
          (0, 244, 248, 0.4) if x >= 200 and x < 400 
          (255, 255, 0, 0.7) if x >= 400 and x < 600 
          (255, 140, 0, 0.8) if x >= 600 else (255, 0, 0, 0.8) for x in myData]

I don't understand if it's because of the indentation or because i added if.. and statements; i tried to remove those and but i still got the error. How can i fix it?

Answer 1

You may use else for each if you use

colors = [(141, 0, 248, 0.4) if x >= 150 and x < 200 else 
          (0, 244, 248, 0.4) if x >= 200 and x < 400 else
          (255, 255, 0, 0.7) if x >= 400 and x < 600 else
          (255, 140, 0, 0.8) if x >= 600 else (255, 0, 0, 0.8) for x in WallData.Qty]

---

A method would be more readable

def apply(x):
    if x >= 150 and x < 200 : return 141, 0, 248, 0.4  
    if x >= 200 and x < 400 : return 0, 244, 248, 0.4  
    if x >= 400 and x < 600 : return 255, 255, 0, 0.7 
    if x >= 600 : return 255, 140, 0, 0.8 
    return 255, 0, 0, 0.8

colors = [apply(x) for x in values]

Answer 2

The reason you get the error is that a list comprehension has the syntax:

[<value expression> for <target> in <iterator> if <condition>]

or

[<value expression> for <target> in <iterator>]

You can't build a list comprehension like you have done, with multiple values in the way you need. The way I would do it would be to have a function that returns the right color tuple for a given x value:

def color_for_x(x):
    ...

and then write your comprehension like this:

color = [color_for_x(x) for x in WallData.Qty]