[jira] Commented: (THRIFT-162) Thrift structures are unhashable, preventing them from being used as set elements

["David Reiss (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/THRIFT-162?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12638132#action_12638132 ] 

David Reiss commented on THRIFT-162:
------------------------------------

My gut feeling is that Thrift structures should not be hashable in Python because they are inherently mutable.  Putting one in a set is really not safe, because you can change the value of some field, which would change the hash and break the set.

> Thrift structures are unhashable, preventing them from being used as set elements
> ---------------------------------------------------------------------------------
>
>                 Key: THRIFT-162
>                 URL: https://issues.apache.org/jira/browse/THRIFT-162
>             Project: Thrift
>          Issue Type: Bug
>          Components: Compiler (Python), Library (Python)
>            Reporter: Esteve Fernandez
>            Priority: Minor
>         Attachments: thrift_py_hash.patch
>
>
> Let Foo be a Thrift structure:
> struct Foo {
>  1: i32 bar
> }
> If you want to use it properly as a set element or a as a dictionary key, the autoegenerated Python code will complain about not being hashable:
> >>> f1 = Foo()
> >>> f1.bar = 1
> >>> f2 = Foo()
> >>> f2.bar = 1
> >>> f1 == f2
> True
> >>> set([f1]) & set([f2])
> set([])
> >>> d = {}
> >>> d[f1] = 2
> Traceback (most recent call last):
>  File "<stdin>", line 1, in <module>
> TypeError: unhashable instance
> Since Thrift structures already implement __eq__ and __ne__, they should implement __hash__ as well. The attached patch tries to mimic the behaviour of the Java compiler, including a HashCodeBuilder class written in Python.

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