Can Python "os.environ.get" ever return a non-string?

Question

In this code here, they use os.environ to get the value of an environment variable, and then immediately check to see if it is an instance of their custom classes.

value = os.environ.get(variable)
...
elif isinstance(value, ConfigList) or isinstance(value, ConfigTree):

Is it actually possible that the value will be an instance of their custom classes? Is this dead code?

Answer 1

Anything that comes from the outside will be just a string, I guess.

On the other hand if you are adding something to the environment from the Python code, then you have just a bit more freedom.

Adding anything but a string still fails:

>>> os.environ['a'] = 89
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\Program Files\Python27\lib\os.py", line 420, in __setitem__
    putenv(key, item)
TypeError: must be string, not int

However, you could make your own class inherited from str:

class C(str):
    pass

os.environ['a'] = C()

In Python2 this seems to do the trick:

>>> type(os.environ['a'])
<class '__main__.C'>

However, in Python 3 it does not. It looks like it just saves a string:

>>> type(os.environ['a'])
<class 'str'>

---

Still, that does not explain the code from pyhocon. I don't see how that object could be pushed into os.environ.

Unless they monkeypatched os.environ... In that case, anything would be possible.