Simon Forman wrote:
...
> I usually use this with assert statements when I need to check a
> sequence. Rather than:
>
> for something in something_else: assert expression
>
> I say
>
> assert False not in (expression for something in something_else)
>
> This way the whole assert statement will be removed if you use the '-O'
> switch to the python interpreter. (It just occurred to me that that's
> just an assumption on my part. I don't know for sure that the
> interpreter isn't smart enough to remove the first form as well. I
> should check that. ;P )
FWIW I did just check that and it seems valid, the second form gets
"optimized" away.
File delme.py:
import dis
N = (True, True, False)
def a():
for n in N:
assert n
def b():
assert False not in (n for n in N)
dis.dis(a)
print '==============================='
dis.dis(b)
Results of running it without '-O':
$ python delme.py
8 0 SETUP_LOOP 28 (to 31)
3 LOAD_GLOBAL 0 (N)
6 GET_ITER
>> 7 FOR_ITER 20 (to 30)
10 STORE_FAST 0 (n)
9 13 LOAD_FAST 0 (n)
16 JUMP_IF_TRUE 7 (to 26)
19 POP_TOP
20 LOAD_GLOBAL 2 (AssertionError)
23 RAISE_VARARGS 1
>> 26 POP_TOP
27 JUMP_ABSOLUTE 7
>> 30 POP_BLOCK
>> 31 LOAD_CONST 0 (None)
34 RETURN_VALUE
===============================
13 0 LOAD_GLOBAL 0 (False)
3 LOAD_CONST 1 (<code object <generator
expression> at 0xb7d89ca0, file "delme.py", line 13>)
6 MAKE_FUNCTION 0
9 LOAD_GLOBAL 1 (N)
12 GET_ITER
13 CALL_FUNCTION 1
16 COMPARE_OP 7 (not in)
19 JUMP_IF_TRUE 7 (to 29)
22 POP_TOP
23 LOAD_GLOBAL 2 (AssertionError)
26 RAISE_VARARGS 1
>> 29 POP_TOP
30 LOAD_CONST 0 (None)
33 RETURN_VALUE
Results of running it with '-O':
$ python -O delme.py
8 0 SETUP_LOOP 14 (to 17)
3 LOAD_GLOBAL 0 (N)
6 GET_ITER
>> 7 FOR_ITER 6 (to 16)
10 STORE_FAST 0 (n)
9 13 JUMP_ABSOLUTE 7
>> 16 POP_BLOCK
>> 17 LOAD_CONST 0 (None)
20 RETURN_VALUE
===============================
13 0 LOAD_CONST 0 (None)
3 RETURN_VALUE
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