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1 # Protocol Buffers - Google's data interchange format | |
2 # Copyright 2008 Google Inc. All rights reserved. | |
3 # http://code.google.com/p/protobuf/ | |
4 # | |
5 # Redistribution and use in source and binary forms, with or without | |
6 # modification, are permitted provided that the following conditions are | |
7 # met: | |
8 # | |
9 # * Redistributions of source code must retain the above copyright | |
10 # notice, this list of conditions and the following disclaimer. | |
11 # * Redistributions in binary form must reproduce the above | |
12 # copyright notice, this list of conditions and the following disclaimer | |
13 # in the documentation and/or other materials provided with the | |
14 # distribution. | |
15 # * Neither the name of Google Inc. nor the names of its | |
16 # contributors may be used to endorse or promote products derived from | |
17 # this software without specific prior written permission. | |
18 # | |
19 # THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS | |
20 # "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT | |
21 # LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR | |
22 # A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT | |
23 # OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, | |
24 # SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT | |
25 # LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, | |
26 # DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY | |
27 # THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT | |
28 # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE | |
29 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. | |
30 | |
31 """Defines a listener interface for observing certain | |
32 state transitions on Message objects. | |
33 | |
34 Also defines a null implementation of this interface. | |
35 """ | |
36 | |
37 __author__ = 'robinson@google.com (Will Robinson)' | |
38 | |
39 | |
40 class MessageListener(object): | |
41 | |
42 """Listens for modifications made to a message. Meant to be registered via | |
43 Message._SetListener(). | |
44 | |
45 Attributes: | |
46 dirty: If True, then calling Modified() would be a no-op. This can be | |
47 used to avoid these calls entirely in the common case. | |
48 """ | |
49 | |
50 def Modified(self): | |
51 """Called every time the message is modified in such a way that the parent | |
52 message may need to be updated. This currently means either: | |
53 (a) The message was modified for the first time, so the parent message | |
54 should henceforth mark the message as present. | |
55 (b) The message's cached byte size became dirty -- i.e. the message was | |
56 modified for the first time after a previous call to ByteSize(). | |
57 Therefore the parent should also mark its byte size as dirty. | |
58 Note that (a) implies (b), since new objects start out with a client cached | |
59 size (zero). However, we document (a) explicitly because it is important. | |
60 | |
61 Modified() will *only* be called in response to one of these two events -- | |
62 not every time the sub-message is modified. | |
63 | |
64 Note that if the listener's |dirty| attribute is true, then calling | |
65 Modified at the moment would be a no-op, so it can be skipped. Performance- | |
66 sensitive callers should check this attribute directly before calling since | |
67 it will be true most of the time. | |
68 """ | |
69 | |
70 raise NotImplementedError | |
71 | |
72 | |
73 class NullMessageListener(object): | |
74 | |
75 """No-op MessageListener implementation.""" | |
76 | |
77 def Modified(self): | |
78 pass | |
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