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More efficient/elegant branching


I have a function with a long if/elif chain that sets a couple of 
variables according to a bunch of test expressions, similar to function 
branch1() below. I never liked that approach much because it is clumsy 
and repetetive, and pylint thinks so as well. I've come up with two 
alternatives which I believe are less efficient due to the reasons given 
in the respective docstrings. Does anybody have a better idea?

def branch1(a, b, z):
     """Inelegant, unwieldy, and pylint complains
     about too many branches"""
     if a > 4 and b == 0:
         result = "first"
     elif len(z) < 2:
         result = "second"
     elif b + a == 10:
         result = "third"
     return result

def branch2(a, b, z):
     """Elegant but inefficient because all expressions
     are pre-computed althogh the first one is most likely
     to hit"""
     decision = [
         (a > 4 and b == 0, "first"),
         (len(z) < 2,       "second"),
         (b + a == 10,      "third")]
     for (test, result) in decision:
         if test: return result

def branch3(a, b, z):
     """Elegant but inefficient because expressions
     need to be parsed each time"""
     decision = [
         ("a > 4 and b == 0", "first"),
         ("len(z) < 2",       "second"),
         ("b + a == 10",      "third")]
     for (test, result) in decision:
         if eval(test): return result
(env) [dh at deham01in015:~/python/rscl_fdc/devel]$