if statement - Is there a best practice for using DRY with several partially overlapping logic streams? -

i unsure how search this, if has been answered, please point me it.

i have once again come upon common situation in unsure of best practice. consider situation in function has 1 of 3 possible values; 'a', 'b', , 'c'.

if receive 'a' or 'b', have a significant amount of overlapping processing do, after case specific stuff. however, if receive 'c', need different. trivial sake of example, have across pretty heavy instances of this.

example (python):

def dostuff(self, val):     if   val == 'a':         self.counter += 1         print val, "is good"         self.passing = true         self.domorestuff()     elif val == 'b':         self.counter += 2         print val, "is not bad"         self.passing = true         self.domorestuff()     elif val == 'c':         self.counter -= 1         self.passing = false         print val, "is unacceptable"         self.wearedonehere() 

so idea either 'a' or 'b', there case-specific instructions , repeated stuff, 'c', it's different. in cases, it's not bad leave 3 separate cases, though makes dry eye twitch @ it. in other cases, if there's lot of repeated code, can bigger problem.

one solution following:

def dostuff(self, val):     if   val == 'a' or val == 'b':         if val == 'a':             self.counter += 1             print val, "is good"         elif val == 'b':             self.counter += 2             print val, "is not bad"         self.passing = true         self.domorestuff()     elif val == 'c':         self.counter -= 1         self.passing = false         print val, "is unacceptable"         self.wearedonehere() 

is double-checking-the-value method okay? makes dry eye twitch little, not as repeating huge blocks of code.

my real question, suppose, has been discussed somewhere or there standard "best practice" way this?

i don't know python, in cases refactor common between , b , put them in private function, call , b.

an example in javascript:

var somefunction = function (somearg) {     var stuffcommontoaandb = function () {         // stuff both , b     };      switch (true) {         case somearg === 'a':             stuffcommontoaandb();             // stuff             break;         case somearg === 'b':             stuffcommontoaandb();             // stuff b             break;         case somearg === 'c':             // stuff c             break;     } }; 

it might worth mentioning passing flags function toggle different behaviors can sign function violating single responsibility principle, in case want take step , rethink design further.