Securely wiping cryptographic secrets in Python

Hi,

if I have a Python program that uses sensitive cryptographic material, is
there a way to securely wipe them from memory after use?

In C, this is usually done by (_carefully_) overwriting the array where
the secrets are stored. Is this possible to do in Python? I bet that if I
try to overwrite a string in Python, there is absolutely no guarantee that
the previous value of that string won't be copied somewhere else
beforehand. What happens if I use a lower level structure, like a
bytearray? Is that property of bytearrays guaranteed somewhere in the
Python spec?

Thanks!