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POQ on Python serialization/deserialization
 

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  1. POQ on Python serialization/deserialization
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    <p>What chances do I have to instantiate, keep and serialize/deserialize to/from binary data Python classes reflecting this pattern (adopted from RFC 2246 [TLS]):</p> <pre><code> enum { apple, orange } VariantTag; struct { uint16 number; opaque string&lt;0..10&gt;; /* variable length */ } V1; struct { uint32 number; opaque string[10]; /* fixed length */ } V2; struct { select (VariantTag) { /* value of selector is implicit */ case apple: V1; /* VariantBody, tag = apple */ case orange: V2; /* VariantBody, tag = orange */ } variant_body; /* optional label on variant */ } VariantRecord; </code></pre> <p>Basically I would have to define a (variant) class VariantRecord, which varies depending on the value of VariantTag. That's not that difficult. The challenge is to find a most generic way to build a class, which serializes/deserializes to and from a byte stream... Pickle, Google protocol buffer, marshal is all not an option. </p> <p>I made little success with having an explicit "def serialize" in my class, but I'm not very happy with it, because it's not generic enough.</p> <p>I hope I could express the problem.</p> <p>My current solution in case VariantTag = apple would look like this, but I don't like it too much</p> <pre><code>import binascii import struct class VariantRecord(object): def __init__(self, number, opaque): self.number = number self.opaque = opaque def serialize(self): out = struct.pack('&gt;HB%ds' % len(self.opaque), self.number, len(self.opaque), self.opaque) return out v = VariantRecord(10, 'Hello') print binascii.hexlify(v.serialize()) &gt;&gt; 000a0548656c6c6f </code></pre> <p>Regards</p>
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    1. USneil
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    1. COWhy aren't you happy with it?
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      1. USDaniel Stutzbach
    2. COWhat is wrong with pickle? Why do you care about somewhat esoteric methods of using C++ when you are using Python? What would you like to have happen? It seems like you want a dense method of storing data, but It is hard to tell what you are really trying to generalize.
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      1. USBear
    3. COI have to implement http://zinfandel.levkowetz.com/html/draft-ietf-p2psip-base-08. Hope that says it all. I have to meet the line protocol, which is binary, but not pickle compliant. I'm not happy with it, because it isn't generic enough :)
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      1. USneil
 

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