A simple package that provide limited supports of goto keyword like C/C++.
Important
This package is only tested locally on Windows amd64 on CPython 3.12.2. Use this package with caution!
from goto import GOTO, LABEL, with_goto
@with_goto
def example_01() -> None:
print("Hello, ")
GOTO.label_01
print("Skipped!")
LABEL.label_01
print("world!")
if __name__ == "__main__":
example_01()- Disassemble the raw function.
- Iterate over the disassembled contents.
- If there‘re
LOAD_GLOBAL (GOTO),LOAD_ATTRandPOP_TOPin continuing 3 lines, note down the byte position and the label, it's where we jump from. - Hack full byte range of above 3 operations to
NOP, except the first 2 bytes ofLOAD_GLOBAL. - If there're
LOAD_GLOBAL (LABEL),LOAD_ATTRandPOP_TOPin continuing 3 lines, note down the byte position the next line ofPOP_TOPand the label, it's where we jump to. - Hack full byte range of above 3 operations to
NOP. - Iterate over all
(label, from_, to)pair, check iffrom_is smaller thanto, to determine there should beJUMP_FORWARDorJUMP_BACKWARD. - Hack the
from_byte position toJUMP_FORWARDorJUMP_BACKWARDaccording to step 7. Iffrom_is far away fromto(jump more than 256 operations), add necessaryEXTENDED_ARG.
Source code
from dis import dis
from goto import GOTO, LABEL, with_goto
@with_goto
def example_01() -> None:
print("Hello, ")
GOTO.label_01
print("Skipped!")
LABEL.label_01
print("world!")
if __name__ == "__main__":
dis(example_01)Raw disassemble content
7 0 RESUME 0
8 2 LOAD_GLOBAL 1 (NULL + print)
12 LOAD_CONST 1 ('Hello, ')
14 CALL 1
22 POP_TOP
9 24 LOAD_GLOBAL 2 (GOTO)
34 LOAD_ATTR 4 (label_01)
54 POP_TOP
10 56 LOAD_GLOBAL 1 (NULL + print)
66 LOAD_CONST 2 ('Skipped!')
68 CALL 1
76 POP_TOP
11 78 LOAD_GLOBAL 6 (LABEL)
88 LOAD_ATTR 4 (label_01)
108 POP_TOP
12 110 LOAD_GLOBAL 1 (NULL + print)
120 LOAD_CONST 3 ('world!')
122 CALL 1
130 POP_TOP
132 RETURN_CONST 0 (None)
Hacked disassemble content
6 0 RESUME 0
8 2 LOAD_GLOBAL 1 (NULL + print)
12 LOAD_CONST 1 ('Hello, ')
14 CALL 1
22 POP_TOP
9 24 JUMP_FORWARD 42 (to 110)
26 NOP
28 NOP
30 NOP
32 NOP
34 NOP
36 NOP
38 NOP
40 NOP
42 NOP
44 NOP
46 NOP
48 NOP
50 NOP
52 NOP
54 NOP
10 56 LOAD_GLOBAL 1 (NULL + print)
66 LOAD_CONST 2 ('Skipped!')
68 CALL 1
76 POP_TOP
11 78 NOP
80 NOP
82 NOP
84 NOP
86 NOP
88 NOP
90 NOP
92 NOP
94 NOP
96 NOP
98 NOP
100 NOP
102 NOP
104 NOP
106 NOP
108 NOP
12 >> 110 LOAD_GLOBAL 1 (NULL + print)
120 LOAD_CONST 3 ('world!')
122 CALL 1
130 POP_TOP
132 RETURN_CONST 0 (None)
- It's able to jump out from nested loop (
fororwhile), but you can't jump into them. - There're 3
EXTENDED_ARGoperation before other operations at most, means that the jumping gap is no more than 4G. You can't jump such that HUGE distance. (This limitation has no chance to reach for human-written source code) - You can't jump to somewhere if they are "dead code" (Python intepreter will remove them directly), such as ...
- Jump out from a
while Trueloop, as the following snippets is unreachable
- Jump out from a
React
Typescript
Django
Laravel
Facebook
Microsoft
Google
Alibaba
D3
Tencent