Determining if a given Python module is a built-in module
Question: I am doing some parsing and introspection of various modules, but I don't want
to parse built-in modules. Now, there is no special type for built-in modules
like there is a `types.BuiltinFunctionType`, so how do I do this?

    
    
    >>> import CornedBeef
    >>> CornedBeef
    <module 'CornedBeef' from '/meatish/CornedBeef.pyc'>
    >>> CornedBeef.__file__
    '/meatish/CornedBeef.pyc'
    >>> del CornedBeef.__file__
    >>> CornedBeef
    <module 'CornedBeef' (built-in)>
    

According to Python, a module is apparently built-in if it doesn't have a
`__file__` attribute. Does this mean that `hasattr(SomeModule, '__file__')` is
the way to check if a module is built in? Surely, it isn't exactly common to
`del SomeModule.__file__`, but is there a more solid way to determine if a
module is built-in?


Answer: ###
[`sys.builtin_module_names`](http://docs.python.org/library/sys.html#sys.builtin_module_names)

> A tuple of strings giving the names of all modules that are compiled into
> this Python interpreter. (This information is not available in any other way
> — modules.keys() only lists the imported modules.)

