Python does not natively provide constructs to talk directly to the hardware, like raw pointers for memory-mapped I/O and many other constructs provided by C/ASM. However, there is proof that most everything in an OS can be written in a more abstracted language; the Singularity OS from Microsoft is written almost exclusively in variants of C#. There's an extremely small amount of C/ASM to do interrupt handlers and such, but everything else, including what most of us consider to be "the kernel" can be done in essentially any Turing-complete language.
It should be noted that Singularity's choice to implement these low-level constructs in C/ASM should not be interpreted as a fundamental limitation of the syntax or other aspects of high-level languages. One could certainly make a variant of Python that emitted and dealt appropriately with the necessary assembly code.
