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From "Samuel Yuan (JIRA)" <>
Subject [jira] [Created] (HIVE-4322) SkewedInfo in Metastore Thrift API cannot be deserialized in Python
Date Tue, 09 Apr 2013 23:30:16 GMT
Samuel Yuan created HIVE-4322:

             Summary: SkewedInfo in Metastore Thrift API cannot be deserialized in Python
                 Key: HIVE-4322
             Project: Hive
          Issue Type: Bug
          Components: Metastore, Thrift API
    Affects Versions: 0.11.0
            Reporter: Samuel Yuan
            Assignee: Samuel Yuan
            Priority: Minor

The Thrift-generated Python code that deserializes Thrift objects fails whenever a complex
type is used as a map key, because by default mutable Python objects such as lists do not
have a hash function. See for related discussion.

The SkewedInfo struct contains a map which uses a list as a key, breaking the Python Thrift
interface. It is not possible to specify the mapping from Thrift types to Python types, or
otherwise we could map Thrift lists to Python tuples. Instead, the proposed workaround wraps
the list inside a new struct. This alone does not accomplish anything, but allows Python clients
to define a hash function for the struct class, e.g.:

def f(object):
    return hash(tuple(object.skewedValueList))

SkewedValueList.__hash__ = f

In practice a more efficient hash might be defined that does not involve copying the list.
The advantage of wrapping the list inside a struct is that the client does not have to define
the hash on the list itself, which would change the behaviour of lists everywhere else in
the code.

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