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From "Matt Anthony (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (THRIFT-4623) Python compiler generates inoperable definitions for default-valued classes in same thrift file
Date Sat, 25 Aug 2018 21:56:00 GMT

    [ https://issues.apache.org/jira/browse/THRIFT-4623?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16592717#comment-16592717
] 

Matt Anthony commented on THRIFT-4623:
--------------------------------------

Would appreciate it. The workaround I found involved making a temp copy of the thrift and
removing the offending elements which is a total hack. The Python that the compiler generates
is very much flawed ... as I mentioned, the __init__ methods reference self.thrift_spec, which
is not defined within the class or prior to it being referenced. For some reason that class
element is defined outside of the class definition, at the very end of the compiled thrift
files. This is not just bad python, it's just generally bad programming to reference an object
in a class initialization that you don't define within the definition. Is there a reason that
thrift_spec can't be defined as a class variable for the class at the time the class definition
is written? It would seem like that must already be known at that time if the rest of the
class definition is written correctly.

> Python compiler generates inoperable definitions for default-valued classes in same thrift
file
> -----------------------------------------------------------------------------------------------
>
>                 Key: THRIFT-4623
>                 URL: https://issues.apache.org/jira/browse/THRIFT-4623
>             Project: Thrift
>          Issue Type: Bug
>          Components: Python - Compiler
>    Affects Versions: 0.11.0
>            Reporter: Matt Anthony
>            Priority: Major
>
> Consider a thrift file as
>  
> <code>
> struct A {
>     i32 value;
> }
>  
> struct B {
>     A itm = {}
> }
> </code>
>  
> The thrift compiler will generate class definitions for A and B, without `self.thrift_spec`
defined, and at the end of the ttypes.py file will go back and populate the thrift_spec objects.
However, in the __init__ method of B, the default value for `itm` would attempt to be set
as `A(**{})`, which will crash with error `AttributeError: 'ObservationInfo' object has no
attribute 'thrift_spec'`. This makes sense since at the time the default object is being established,
there is no thrift_spec object.
> Removing the default value removes the error, but this is not correct behavior. The most
obvious fix is that the `thrift_spec` object of each class needs to be defined within the
class as the class is written, not at the end of the file after all the class objects are
established. Moreover, that is generally good practice and is actually part of the PEP prescriptions
for python (referencing objects before initialization in a class is a highlighted warning,
for this very reason).



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