goto for Python

http://entrian.com/goto/
看了看原始碼，原來是通過給所有函數修改trace，然後在異常時就會執行設定的函數
# Install the trace function, including all preceding frames.
sys.settrace(_trace)
frame = sys._getframe().f_back
while frame:
    frame.f_trace = _trace
    frame = frame.f_back
改天有時間看看如何在trace中分析每一行代碼的！

# Example 1: Breaking out from a deeply nested loop:
from goto import goto, label
for i in range(1, 10):
for j in range(1, 20):
for k in range(1, 30):
print i, j, k
if k == 3:
goto .end
label .end
print "Finished\n"


# Example 2: Restarting a loop:
from goto import goto, label
label .start
for i in range(1, 4):
print i
if i == 2:
try:
output = message
except NameError:
print "Oops - forgot to define 'message'!  Start again."
message = "Hello world"
goto .start
print output, "\n"