>> os.environ["ASD"] = "asd">>> os ..."/>
Date

It doesn't actually remove things from the environment, just from its local copy of the environment. The Python developers seem to simply have left it out of their implementation in os.py. Gustavo Niemeyer noticed this one.

>>> import os
>>> os.system("echo $ASD")

0
>>> os.environ["ASD"] = "asd"
>>> os.system("echo $ASD")
asd
0
>>> os.environ.pop("ASD")
'asd'
>>> os.system("echo $ASD")
asd
0