goto.py

import sys

if not sys.gettrace():
	# f_trace doesn't work if settrace isn't set
	sys.settrace(lambda a, b, c: None)

def j(n):
	def hook(fr, event, arg):
		assert event == "opcode"
		fr.f_lineno += n
		fr.f_trace = oldhook
		fr.f_trace_opcodes = oldtraceops
		if oldtraceops and oldhook:
			return oldhook(fr, event, arg)

	fr = sys._getframe().f_back
	oldhook = fr.f_trace
	oldtraceops = fr.f_trace_opcodes
	fr.f_trace = hook
	fr.f_trace_opcodes = True

a = 1
j(3)
a = 2
print(1)
print(2)
if a == 1:
	j(-4)
print(4)