More efficient/elegant branching

[Antoon Pardon]

On 9/12/19 12:27, Musbur wrote:
> Hello,
>
> 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]$
>
Well if you really want to go this route, you may consider the following:

def branch4(a, b, z):
    decision = [
        ((lambda: a > 4 and b == 0), "first"),
        ((lambda: len(z) < 2), "second"),
        ((lambda: b + a == 10), "third")]
    for test, result in decision:
        if test(): return result