python goto 包

# 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"


# Example 3: Cleaning up after something fails:
from goto import goto, label

# Imagine that these are real worker functions.
def setUp(): print "setUp"
def doFirstTask(): print 1; return True
def doSecondTask(): print 2; return True
def doThirdTask(): print 3; return False  # This one pretends to fail.
def doFourthTask(): print 4; return True
def cleanUp(): print "cleanUp"

# This prints "setUp, 1, 2, 3, cleanUp" - no "4" because doThirdTask fails.
def bigFunction1():
    setUp()
    if not doFirstTask():
        goto .cleanup
    if not doSecondTask():
        goto .cleanup
    if not doThirdTask():
        goto .cleanup
    if not doFourthTask():
        goto .cleanup

    label .cleanup
    cleanUp()

bigFunction1()
print "bigFunction1 done\n"


# Example 4: Using comefrom to let the cleanup code take control itself.
from goto import comefrom, label
def bigFunction2():
    setUp()
    if not doFirstTask():
        label .failed
    if not doSecondTask():
        label .failed
    if not doThirdTask():
        label .failed
    if not doFourthTask():
        label .failed

    comefrom .failed
    cleanUp()

bigFunction2()
print "bigFunction2 done\n"


# Example 5: Using a computed goto:
from goto import goto, label

label .getinput
i = raw_input("Enter either ‘a‘, ‘b‘ or ‘c‘, or any other letter to quit: ")
if i in (‘a‘, ‘b‘, ‘c‘):
    goto *i
else:
    goto .quit

label .a
print "You typed ‘a‘"
goto .getinput

label .b
print "You typed ‘b‘"
goto .getinput

label .c
print "You typed ‘c‘"
goto .getinput

label .quit
print "Finished\n"


# Example 6: What happens when a label is missing:
from goto import goto, label
label .real
goto .unreal      # Raises a MissingLabelError exception.