eryksun added the comment:
In interactive mode the extra reference is held by the "_" built-in variable.
>>> a
'test string A'
>>> del __builtin__._; sys.getrefcount(a) - 1
1
Look at the following disassembled code, compiled in the 'single' interactive
mode:
>>> dis.dis(compile('a', '', 'single'))
1 0 LOAD_NAME 0 (a)
3 PRINT_EXPR
4 LOAD_CONST 0 (None)
7 RETURN_VALUE
[PRINT_EXPR][1] calls [sys.displayhook][2]. The default display hook prints a
non-None value and sets it as __builtin__._. You can replace this with your own
display hook. The original function is always available as sys.__displayhook__.
[1]: https://hg.python.org/cpython/file/v2.7.10/Python/ceval.c#l1727
[2]: https://docs.python.org/2/library/sys.html#sys.displayhook
----------
nosy: +eryksun
resolution: -> not a bug
stage: -> resolved
status: open -> closed
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<http://bugs.python.org/issue25273>
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