"""
(4) str in __all__ (list of str):

os.py:

    if "putenv" not in __all__:
        __all__.append("putenv")
"""

For this example: "putenv" is probably interned by "def putenv(...)". "putenv" string and the name of the function are the same constant. When a function is defined, it is stored in the locals dictionary, so the key ("putenv") is interned by PyDict_SetItem().

So dict is not used explicitly, but implicitly by the namespace.