Serhiy Storchaka added the comment:
Some examples.
if not a and b: x
Unpatched:
1 0 LOAD_NAME 0 (a)
2 UNARY_NOT
4 POP_JUMP_IF_FALSE 14
6 LOAD_NAME 1 (b)
8 POP_JUMP_IF_FALSE 14
10 LOAD_NAME 2 (x)
12 POP_TOP
>> 14 LOAD_CONST 0 (None)
16 RETURN_VALUE
Patched:
1 0 LOAD_NAME 0 (a)
2 POP_JUMP_IF_TRUE 12
4 LOAD_NAME 1 (b)
6 POP_JUMP_IF_FALSE 12
8 LOAD_NAME 2 (x)
10 POP_TOP
>> 12 LOAD_CONST 0 (None)
14 RETURN_VALUE
if a <= b < c: x
Unpatched:
1 0 LOAD_NAME 0 (a)
2 LOAD_NAME 1 (b)
4 DUP_TOP
6 ROT_THREE
8 COMPARE_OP 1 (<=)
10 JUMP_IF_FALSE_OR_POP 18
12 LOAD_NAME 2 (c)
14 COMPARE_OP 0 (<)
16 JUMP_FORWARD 4 (to 22)
>> 18 ROT_TWO
20 POP_TOP
>> 22 POP_JUMP_IF_FALSE 28
24 LOAD_NAME 3 (x)
26 POP_TOP
>> 28 LOAD_CONST 0 (None)
30 RETURN_VALUE
Patched:
1 0 LOAD_NAME 0 (a)
2 LOAD_NAME 1 (b)
4 DUP_TOP
6 ROT_THREE
8 COMPARE_OP 1 (<=)
10 POP_JUMP_IF_FALSE 20
12 LOAD_NAME 2 (c)
14 COMPARE_OP 0 (<)
16 POP_JUMP_IF_FALSE 28
18 JUMP_FORWARD 4 (to 24)
>> 20 POP_TOP
22 JUMP_FORWARD 4 (to 28)
>> 24 LOAD_NAME 3 (x)
26 POP_TOP
>> 28 LOAD_CONST 0 (None)
30 RETURN_VALUE
if not (a and b) and c: x
Unpatched:
1 0 LOAD_NAME 0 (a)
2 JUMP_IF_FALSE_OR_POP 6
4 LOAD_NAME 1 (b)
>> 6 UNARY_NOT
8 POP_JUMP_IF_FALSE 18
10 LOAD_NAME 2 (c)
12 POP_JUMP_IF_FALSE 18
14 LOAD_NAME 3 (x)
16 POP_TOP
>> 18 LOAD_CONST 0 (None)
20 RETURN_VALUE
Patched:
1 0 LOAD_NAME 0 (a)
2 POP_JUMP_IF_FALSE 8
4 LOAD_NAME 1 (b)
6 POP_JUMP_IF_TRUE 16
>> 8 LOAD_NAME 2 (c)
10 POP_JUMP_IF_FALSE 16
12 LOAD_NAME 3 (x)
14 POP_TOP
>> 16 LOAD_CONST 0 (None)
18 RETURN_VALUE
Note that the __bool__() method of every value is evaluated only once.
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Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue30501>
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