Python simplify checking multiple boolean conditions

Question

I have a function that checks 3 different boolean flags and has a unique outcome for each of the 8 combinations.

""" a | b | c | out - + - + - + --- 0 | 0 | 0 | 0 0 | 0 | 1 | 1 0 | 1 | 0 | 2 0 | 1 | 1 | 3 1 | 0 | 0 | 4 1 | 0 | 1 | 5 1 | 1 | 0 | 6 1 | 1 | 1 | 7 """ def do_stuff(a, b, c): if a: if b: if c: return function7() # a, b, c return function6() # a, b, !c if c: return function5() # a, !b, c return function4() # a, !b, !c else: if b: if c: return function3() # !a, b, c return function2() # !a, b, !c if c: return function1() # !a, !b, c return function0() # !a, !b, !c

I'm already short-cutting a lot of else statements since I'm returning (exiting the loop).

Is there a more DRY way to accomplish this? I could convert to binary, and do a single depth level of if/elif, but I don't want to use "magic numbers".

Also, I realize this is only 16 lines of code for 8 outcomes, but what if it were 4 variables, is there a way to increase readability/flow?

@ReutSharabani the functions call a redirect to unique Django views — j_syk
– j_syk, Commented Dec 2, 2015 at 21:23
do you really need 8 views? are they that different? This seems like not the best deaign. I could be wrong though. — Reut Sharabani
– Reut Sharabani, Commented Dec 2, 2015 at 21:25
@ReutSharabani well, it maybe could be a little more concise, but it's not within the scope to rewrite the underlying functions. Basically this function processes a user submitted web form and generates a pdf. So the various booleans change a print template, filter by a customer, and filter past due. Regardless of the actual use case, it peeked my curiosity about ways to process multiple bools — j_syk
– j_syk, Commented Dec 2, 2015 at 21:29

Mad Physicist · Accepted Answer · 2015-12-02 21:20:07Z

You need to have some sort of mapping from outcome to function and a mapping from input to outcome. The nifty table you provide at the top, combined with the fact that bools in Python are just the integers 0 and 1 gives you the following:

outcomeToFunc { 0: function0, 1: function1, 2: function2, 3: function3, 4: function4 # etc... } def inputToOutcome(a, b, c): return a << 2 | b << 1 | c def do_stuff(a, b, c): outcome = inputToOutcome(a, b, c) return outcomeToFunc[outcome]()

If you are interested in having an arbitrary number of boolean inputs, you can modify do_stuff and inputToOutcome to use varargs:

outcomeToFunc { 0: function0, 1: function1, 2: function2, 3: function3, 4: function4 # etc... } def inputToOutcome(*args): outcome = 0 n = len(args) - 1 for ind, arg in enumerate(args): outcome |= bool(arg) << (n - ind) return outcome def do_stuff(*args): outcome = inputToOutcome(*args) try: return outcomeToFunc[outcome]() except KeyError: raise ValueError('Outcome {} not supported'.format(outcome))

Robᵩ · Accepted Answer · 2015-12-02 21:15:01Z

Here are two solutions. It is up to you to decide if they are prettier than the one you presented.

def do_stuff(a, b, c): flags = bool(a), bool(b), bool(c) if flags == (True, True, True): return function7() if flags == (True, True, False): return function6() if flags == (True, False, True): return function5() if flags == (True, False, False): return function4() if flags == (False, True, True): return function3() if flags == (False, True, False): return function2() if flags == (False, False, True): return function1() if flags == (False, False, False): return function0() def do_stuff(a, b, c): control = { (True, True, True): function7, (True, True, False): function6, (True, False, True): function5, (True, False, False): function4, (False, True, True): function3, (False, True, False): function2, (False, False, True): function1, (False, False, False): function0, } return control[bool(a), bool(b), bool(c)]()

mhbashari · Accepted Answer · 2015-12-02 21:33:16Z

First you can build a binary to decimal converter.After obtaining the new number you can call the method by function name in an string by eval function:

def function0(): print("function0") def function1(): return 1; a = eval("function1()") print(a)

Remember that you can pass global variables to eval function unless the current global names id used.

Collectives™ on Stack Overflow

Python simplify checking multiple boolean conditions

3 Answers 3

1 Comment

Comments

3 Comments

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

1 Comment

Comments

3 Comments

Related