Question

If I print os.environ, the output looks like a dictionary. Some posts I read online say that it is a memory based dictionary.
But it does not support .viewkeys() method and tells me that: _Environ instance does not support this method. So what is the exact type of os.environ. If I try:

print type(os.environ)

I get instance as the answer.

Can please clarify this behavior of os.environ?

Answer 1

>>> os.environ.__class__
<class os._Environ at 0xb7865e6c>

It is a subclass of UserDict.IterableUserDict.

In python 2.7 the source can be found is in os.py on line 413 (Windows) and line 466 (Posix). Here is the python 3.2 source.