[Scons-users] Reading Python 3.8.0 .dblite file from Python 2.7

Mats Wichmann mats at wichmann.us
Tue Dec 3 19:47:53 EST 2019

On 12/3/19 5:35 PM, Don Baldwin wrote:
> Hi,

>     ignoring invalid `dblite' file
>  From what I've read, this seems to be due to the incompatibility 
> between the pickle library between Python 2 and 3.

evolving protocols, yes. actually it's not just py 2/3, 3.8 added a new 
pickle protocol that earlier Py3's can't read.

> I see the following code in lib/SCons/compat/__init__.py:
>     # Was pickle.HIGHEST_PROTOCOL
>     # Changed to 2 so py3.5+'s pickle will be compatible with py2.7.
> When I modify this to set PICKLE_PROTOCOL = 2, my tools are able to 
> successfully read the .dblite files, but I'd prefer not to have to 
> modify the native SCons code.
> Is there a way to set this value from my SConscript file, or some other 
> preferred way to handle this situation?
No.  SCons picks the highest available pickle version which is arguably 
a dubious choice for your situation (and mine, it turns out), but that's 
what it does.  There's no official API-ish way to request a different 
one.  that would be a feature request, I guess.

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