goto-python's Introduction

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.

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goto-python's Issues

Support for Python 3.10?

Is there a timeline on support for Python 3.10?

I have found this module to be extremely useful for quick porting of old and poorly coded Fortran to python, but I am stuck with Python 3.9, would be great to see support for >= 3.10

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