python: Piping a value through an if/elif statement
This question already has an answer here:
Probably not what you want, but one option is to use a dictionary of functions:
def do_a();
..
def do_b();
..
def do_c();
..
strategy = {
a: do_a,
b: do_b
c: do_c
}
strategy[f()]()
But normally you'd want some error handling in case the dictionary entry wasn't found, in which case you'd likely end up with a separate variable anyway, plus you now have to extract each case into its own function.
Maybe even less relevant, if there are only two cases you can use a ternary operator:
do_a() if f() == a else do_b()
Though likely you already know this, plus your question has more than two cases, plus lots of people don't like the ternary operator, but anyway.
If you have a language with a switch statement, like C#/Java/C++ etc, or a pattern matching statement, like any of Haskell/OCaml/F#/Scala/Erlang etc, then you can use those. A pattern matching statement looks like this:
match f() with
| a ->
// do something
// and maybe something else too
| b ->
// do some other thing
// and yet some other thing
but there is no such feature in Python.
If you only want to map answers (without computing further), then you can solve it with a simple mapping function (similar to junichiro's answer):
import random
def f():
foo = ['a', 'b', 'c', 'd', 'e']
return random.choice(foo)
if __name__ == '__main__':
from_to = dict(a=2, b=1, c=3, d=4, e=5)
print(from_to.get(f(), None))
In case you have an unforeseen value from f() then from_to.get(f(), None) would default to None
There is no way to do this with if/elif and Python does not have a switch statement. You need the temporary variable.
You can alternatively use a dispatch table if you know the exact values of a, b, and c. It's a little more verbose, but if you have a lot of possible branches, it will be faster and possibly easier to follow.
To make a dispatch table:
return DISPATCH_TABLE[f()]() You can find some examples here.
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