[issue39375] Document os.environ[x] = y and os.putenv() as thread unsafe

Daniel Martin added the comment: See also https://bugs.python.org/issue40961 - that bug is not about thread safety, but another quirk around env. variable setting that needs to be documented in the documentation for os.putenv and os.getenv, and so anyone addressing this bug should probably

[issue40961] os.putenv should be documented as not affecting os.getenv's return value

New submission from Daniel Martin : I find this behavior extremely surprising: $ ABC=def python Python 3.7.4 (v3.7.4:e09359112e, Jul 8 2019, 14:54:52) [Clang 6.0 (clang-600.0.57)] on darwin Type "help", "copyright", "credits" or "license" for more infor