README.md

Installation

Compatible with python 3.9 or newer.
tested with python 3.9.

pip install goto-label

• goto-python only work with python 3.9, idk about 3.10.
• use at your own risk, the author of this module is not responsible if there is a problem with your app.

Features

• does not add unnecessary NOP instructions to the code.
• automatically add push/pop block instructions if necessary.
  for example, if you jump out of for block, it automatically pop the iterator from the stack (as break does).

Limitations

• can't jump into with, for, except, and finally block. but can jump out of it.

Syntax

• goto .name jump to name.
• label .name define label name.

Usage

1. as a decorator of a function

from goto import with_goto

@with_goto
def example():
  goto .end
  print("this will not print")
  label .end
  print("this will print")

example()

# output:
# this will print

2. patching code object

from goto import patch
import dis

# make code object
codestring = "goto .lbl; label .lbl"
code = compile(codestring, "<string>", "exec")

# patch code object
newcode = patch(code)

print("original:")
dis.dis(code)
print("modified:")
dis.dis(newcode)

# original:
#  1       0 LOAD_NAME            0 (goto)
#          2 LOAD_ATTR            1 (lbl)
#          4 POP_TOP
#          6 LOAD_NAME            2 (label)
#          8 LOAD_ATTR            1 (lbl)
#         10 POP_TOP
#         12 LOAD_CONST           0 (None)
#         14 RETURN_VALUE
# modified:
#  1       0 JUMP_ABSOLUTE        2
#    >>    2 LOAD_CONST           0 (None)
#          4 RETURN_VALUE

Examples of good gotos in python (IMO)

labeled break/continue

for _ in ...:
  for _ in ...:
    if should_break:
      goto .br  # break outer loop
label .br

for _ in ...:
  for _ in ...:
    if should_continue:
      goto .con  # continue outer loop
  label .con

this module brandtbucher/hax, can do the same job as goto-python does, but it requires you to have basic knowledge of python bytecode.