How to prohibit a Python module from calling other modules?

You can use "Sandboxed Python". A "Sandboxed Python" would let you permit or forbid modules, limit execution slices, permit or deny network traffic, constrain filesystem access to a particular directory (floated as "/"), and so on. It is also referred to as RestrictedExecution. There are many ways to implement sandboxing on Python. You could Modify the CPython Runtime, Use Another Runtime, Use Operating System Support, etc to implement such a sandbox. You can read more about sandboxing at: https://wiki.python.org/moin/SandboxedPython

Pypi has a package called RestrictedPython(https://pypi.python.org/pypi/RestrictedPython) that is a defined subset of the Python language which allows to provide a program input into a trusted environment. RestrictedPython is not a sandbox system or a secured environment, but it helps to define a trusted environment and execute untrusted code inside of it.