I'm looking to implement a shared configuration file that will be written (output) in python, but be read (input) in C.
The only prerequisite of this configuration file is that it can't be human readable.
Anyone have any suggestions on what file format I should use for this project?
Edit:  The file can't be human readable because we don't want the user to be able to modify the configuration, also, in some cases, we don't want the user to know about certain configurations.
How secure do you need this config file to be?
There is no absolute security, you'll quickly run into DRM like issues (allow users to open a file but not allow them to open it ... I know it's insane).
Often simple obfuscation is quite effective.  Dump the config to a JSON file (please don't use xml).  XOR the contents and change the extension.  That will stop all casual inspection of the file.  Obviously don't document that this is your obfuscation procedure.
If you're worried about user modification of config files (you don't care if the configs are readable you just want prevent loading custom configs) use a cryptographic signature.  Store the private key at your company and use it and the python app to generate a signed configuration.  Store the public key in the c++ application and use it to verify the config is properly signed before applying the settings.
Shared configuration file format between python and C?