Refactoring long statement in Python

Question

I have a very long conditional statement for deciding what action to take for a pair of variables a and b.

action = 0 if (a==0) else 1 if (a>1 and b==1) else 2 if (a==1 and b>1) else 3 if (a>1 and b>1) else -1

While it is nice with the compactness (in lines;) ) of this statement, it must exist a more elegant way to do this?

Tim Pietzcker · Accepted Answer · 2010-10-03 18:58:58Z

9

if a==0:
   action = 0
elif a>1 and b==1:
   action = 1
elif a==1 and b>1:
   action = 2
elif a>1 and b>1:
   action = 3
else:
   action = -1

From the Zen of Python (excerpts):

Simple is better than complex.
Flat is better than nested.
Readability counts.

edited Oct 3, 2010 at 18:58

answered Oct 3, 2010 at 18:50

Tim Pietzcker

337k59 gold badges520 silver badges572 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

AndiDog Over a year ago

Parentheses are also unnecessary.

Tim Pietzcker Over a year ago

@AndiDog: Thanks, I hadn't even looked at them :)

PaulMcG Over a year ago

This form also makes it much easier to see that the (a==1 and b==1) case has been omitted.

Theodor Over a year ago

Very intressting. This is what my code looked like before I started fiddeling with it and ended up with the super long statement =) @Andi Parentheses where to make it more readable. @Paul (a==1 and b==1) has been intetionally omitted - it is covered by else -1, good point though, it is not readily apparent.

Tim Pietzcker Over a year ago

@Theodor: There you have it: Python makes it natural to write good code. If you need to add something to make it more readable (like the parentheses in your "ternary operator cascade"), you probably need to rethink what you're doing :)

Russell Borogove · Accepted Answer · 2010-10-03 19:04:13Z

2

If a and b both have known, small, integer ranges, you could make a dict. Say they're both always 0,1, or 2:

actionTable = { (0,0): 0, (0,1): 0, (0,2): 0,
                (1,0):-1, (1,1):-1, (1,2): 2,
                (2,0):-1, (2,1): 1, (2,2): 3 }

return actionTable[ (a,b) ]

But this is a little bit opaque, unscalable, and hard to maintain. If the action table is big and complex and able to be generated programmatically, though, it's a useful technique for the toolbox.

answered Oct 3, 2010 at 19:04

Russell Borogove

19.1k4 gold badges46 silver badges53 bronze badges

1 Comment

Theodor Over a year ago

I like the look up table idea, however, a and b can (in theory) take arbitrary large values. I'll keep it in memory though.

Collectives™ on Stack Overflow

Refactoring long statement in Python

2 Answers 2

5 Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

5 Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related