Calling the "forward" method transfers processing to a new screen. It never returns. This code is taken from multiple places, so I haven't bothered to keep the classes intact, I've just taken the meat. More generally, this is an example of state machine with a main loop. At any point, you can say, "I'm ready to change state. Do it. Go back to the loop. Don't return--just throw away my current stack."
Python, 113 lines
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Copy to clipboard1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 | """Forward processing to a new screen."""
__docformat__ = "restructuredtext"
def forward(self, screen, *args, **kargs):
"""Forward processing to a new screen. This method does not return.
Generate a ``Forward`` exception which
aquarium.util.Aquarium.screenLoop_ class is prepared to catch.
screen
This is the module name of the screen relative to the screen
directory.
``*args``, ``**kargs``
The arguments to pass to the screen's ``__call__`` method.
.. _aquarium.util.Aquarium.screenLoop:
aquarium.util.Aquarium.Aquarium-class.html#screenLoop
"""
raise Forward(screen, *args, **kargs)
class Forward(Exception):
"""Raise an instance of this class to make Aquarium do a forward.
Actually, you should use aquarium.util.InternalLibrary.forward_ to do that
for you.
The following attributes are used:
screen
The module name of the screen relative to the ``screen`` directory
``*args``, ``**kargs``
The arguments to pass to the screen's ``__call__`` method.
.. _aquarium.util.InternalLibrary.forward:
aquarium.util.InternalLibrary.InternalLibrary-class.html#forward
"""
def __init__(self, screen, *args, **kargs):
"""Just accept the parameters."""
Exception.__init__(self)
self.screen = screen
self.args = args
self.kargs = kargs
def screenLoop(self):
"""Show the desired screen, and loop around to handle exceptions.
By using a loop, the same code path can be used for exceptions. In
fact:
* The aquarium.util.InternalLibrary.Forward_ exception results in
looping around to show the desired screen to forward to.
* ``ImportError``'s and ``AttributeError``'s while trying to import the
screen result in the ``not_found`` screen.
* Any other ``Exception`` results in the ``exception`` screen.
Be especially wary of infinite loops since we're catching all
exceptions and looping around. Use ``handleDoubleException`` in these
cases, but note that it too will raise an exception, by design.
If a screen runs successfully to completion, call
``self._ctx.dba.commit()`` and return whatever the screen returns.
.. _aquarium.util.InternalLibrary.Forward:
aquarium.util.InternalLibrary.Forward-class.html
"""
from InternalLibrary import Forward
class _Continue(Exception): pass # Can't use continue in an except.
MAX_FORWARDS = 1024
ctx = self._ctx
if hasattr(ctx, "screen"): # We had an exception in initAll.
screen, args, kargs = ctx.screen, ctx.args, ctx.kargs
else:
screen, args, kargs = ctx.url.whichScreen(), (), {}
self._prevExc, self._prevExcInfo = None, None
if not screen:
screen = properties.DEFAULT_SCREEN
if not ctx.iLib.validModuleName(screen):
screen, args, kargs = "not_found", (screen,), {}
for _ignored in xrange(MAX_FORWARDS):
try:
ctx.screen = screen
try:
ctx.screenInstance = ctx.iLib.aquariumFactory(
"screen." + screen)
except (ImportError, AttributeError), e:
self.catchDoubleException(e)
screen, args, kargs = "not_found", (e), {}
raise _Continue
buf = ctx.iLib.inverseExtend(ctx.screenInstance.__call__,
*args, **kargs)
if properties.USE_DATABASE:
ctx.dba.commit()
return buf
except _Continue:
pass
except Forward, e:
screen, args, kargs = e.screen, e.args, e.kargs
except Exception, e:
self.catchDoubleException(e)
screen, args, kargs = "exception", (exc_info(),), {}
raise OverflowError("Too many forwards")
|
Note that this comes from the Aquarium Web application framework, but any references to Aquarium can easily be removed.
Tags: shortcuts
