David Harvey wrote:
> Suppose I write
>
> if x in ("abc", "def", "xyz"):
> doStuff()
>
> elif x in ("pqr", "tuv", "123"):
> doOtherStuff()
>
> elif ...
> When is python building the tuples? Does it need to build the tuple
> every time it comes through this code? Or does it somehow recognise
> that they are constant and cache them?
when in doubt, ask the compiler:
def code(x):
if x in ("abc", "def", "xyz"):
doStuff()
elif x in ("pqr", "tuv", "123"):
doOtherStuff()
import dis
dis.dis(code)
prints:
2 0 LOAD_FAST 0 (x)
3 LOAD_CONST 7 (('abc', 'def', 'xyz'))
6 COMPARE_OP 6 (in)
9 JUMP_IF_FALSE 11 (to 23)
12 POP_TOP
3 13 LOAD_GLOBAL 1 (doStuff)
16 CALL_FUNCTION 0
19 POP_TOP
20 JUMP_FORWARD 25 (to 48)
>> 23 POP_TOP
4 24 LOAD_FAST 0 (x)
27 LOAD_CONST 8 (('pqr', 'tuv', '123'))
30 COMPARE_OP 6 (in)
33 JUMP_IF_FALSE 11 (to 47)
36 POP_TOP
5 37 LOAD_GLOBAL 2 (doOtherStuff)
40 CALL_FUNCTION 0
43 POP_TOP
44 JUMP_FORWARD 1 (to 48)
>> 47 POP_TOP
>> 48 LOAD_CONST 0 (None)
51 RETURN_VALUE
so the answer is "yes, in this specific case".
> (The tuples I have in mind are of course much longer than three
> elements)
in that case, you should probably use pre-calculated sets instead of tuples.
</F>
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