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https://issues.apache.org/jira/browse/THRIFT-2642?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16056824#comment-16056824
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Eric Conner commented on THRIFT-2642:
-------------------------------------
Hi everyone,
I finally had some time to take a stab at fixing this.
I more or less followed the fbthrift approach with a few modifications. At a
high level, the change:
# Moves all thrift_spec definitions to the end of the ttypes or service file.
# Changes the initial declaration of thrift_spec to (<Struct>, None)
# Uses a method call ``fix_spec`` to fill in the spec to (<Struct>,
<Struct>.thrift_spec)
The fbthrift approach is similar except their struct definition uses a list
[<Struct>, <Struct>.thrift_spec]. I looked at this route for awhile, but
Apache Thrift's fastbinary implementation depends pretty heavily on
``thrift_spec`` being immutable. There are ref counting assumptions I don't
fully understand that led to lots of complications when I tried to change
things to use lists (see
https://github.com/apache/thrift/blob/19baeefd8c38d62085891d7956349601f79448b3/lib/py/src/ext/protocol.tcc#L341).
Instead, I'm using a modified version of fbthrift's fix_spec script
(https://github.com/facebook/fbthrift/blob/3ef868c969464e935b39e336807af1486b2739c3/thrift/lib/py/util/Recursive.py).
The main change I made was to convert each spec to a list, modify the list
recursively, and then convert the list back to a tuple. I'm unsure of the
performance hit this adds, but I figured it wouldn't be too bad since it only
happens at import time.
> Recursive structs don't work in python
> --------------------------------------
>
> Key: THRIFT-2642
> URL: https://issues.apache.org/jira/browse/THRIFT-2642
> Project: Thrift
> Issue Type: Bug
> Components: Python - Compiler, Python - Library
> Affects Versions: 0.9.2
> Reporter: Igor Kostenko
>
> Recursive structs in 0.9.2 work fine in c++ & c#, but not in python, because
> generated code trying to use objects which not constructed yet.
> Struct:
> {code}
> struct Recursive {
> 1: list<Recursive> Children
> }
> {code}
> Python code:
> {code}
> class Recursive:
> thrift_spec = (
> None, # 0
> (1, TType.LIST, 'Children', (TType.STRUCT,(Recursive,
> Recursive.thrift_spec)), None, ), # 1
> )
> {code}
> Error message:
> {code}
> Traceback (most recent call last):
> File "ttypes.py", line 20, in <module>
> class Recursive:
> File "ttypes.py", line 28, in Recursive
> (1, TType.LIST, 'Children', (TType.STRUCT,(Recursive,
> Recursive.thrift_spec)), None, ), # 1
> NameError: name 'Recursive' is not defined
> {code}
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