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The problem is that a warning is emited before the _warnings module is initialized: get_filter() uses _filters which is equal to NULL.
Attached patch initialize the _warnings module (but not the warnings module) before initfsencoding(). initfsencoding() is the first function loading modules (especially the encoding package) and so _warnings have to be initialized before.
The patch does also fix get_filter() to avoid the crash. This fix alone is not enough to fix this issue: Python cannot start because PyErr_WarnEx() returns -1 if _warnings is not initialized yet.
I tried to display the warning (Not importing directory '/tmp/encodings': missing __init__.py) but it looks to be impossible: display a warning requires that warnings is loaded, but import warnings emits the warning. warnings imports indirectly encodings (linecache -> tokenize -> codecs). I consider that avoiding the crash is enough :-)
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The encodings can be not empty: the crash occurs if there is an encoding directory is sys.path without the __init__.py file.
 $ mkdir encodings
 $ touch encodings/a
 $ touch encodings/b
 $ touch encodings/c
 $ PYTHONPATH=$PWD ./python 
 Erreur de segmentation