[issue45944] Avoid calling isatty() for most open() calls

[Serhiy Storchaka]

Change by Serhiy Storchaka <storchaka+cpython at gmail.com>:


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nosy: +benjamin.peterson, pitrou, stutzbach
versions:  -Python 3.10, Python 3.6, Python 3.7, Python 3.8, Python 3.9

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue45944>
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