Tips For Lowering Indention Levels

Linus Torvalds, the creator of linux, sets his tabs/indentations to 8 spaces. Personally that seems a little wide, but he says some interesting things about why shorter isn’t necessarily better. Me, I’ll stay with 4 because it just looks right. But you still shouldn’t have too many indent levels.

“If you need more than 3 levels of indentation, you’re screwed anyway, and should fix your program.” – Linus Torvalds, Linux Kernel Coding Style

Use Continue

Example:

for item in sequence:
     if is_valid(item):
          if not is_inconsequential(item):
               item.do_something()

Becomes:

for item in sequence:
     if not is_valid(item):
          continue
     if is_inconsequential(item):
          continue
     item.do_something()

Notice you have to flip the values of your if statements making this change. This only works inside a loop and if your language has continue.

Factor Out A New Method

This is true for a lot of things. As I recently heard if a method starts to get over 10-15 lines it starts to feel like maybe I’m doing something wrong.

If your indents are starting to get deep, maybe some of those sub-levels should just be put in their own routine.

On a python related note, Mr Rhodes points out if you need a new routine and you are in a class, your natural thought is to make a new method on the object. But if you aren’t using self – referring to the object in your new method – you can just make a function. These become easier to test and easier to move.

Factor Out An Iterator

Mr Rhodes says iterators are a Python superpower. I don’t understand python iterators yet and didn’t even understand his example, in the interest of completeness, here’s his example.

Example:

for item in sequence:
     for widget in item:
          for pixel in bitmap:
               pixel.align()
               pixel.darken()
               pixel.draw()

becomes:

def widget_pixels(sequence):
     for item in sequence:
          for widget in item:
               for bitmap in widget:
                    for pixel in bitmap:
                         yield pixel
 
for pixel in widget_pixels(sequence):
     pixel.align()
     pixel.darken()
     pixel.draw()

Lastly he talked about going to an argument per line for function calls. I want to write a full post on this idea because it has some cool implications in version control. The short version is once a function call gets to 79 characters, just go right to putting each parameter on its own line.

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