Dynamically creating module in sys.modules causes sys to become None

Question

I'm creating a module called Qt (Github link) where I alias another module (for example PyQt4), so that when I import Qt I am in fact importing PyQt4:

from Qt import QtWidgets  # this really imports PyQt4.QtGui

Example Qt module:

# Qt.py
import sys
import PyQt4.Qt

sys.modules["Qt"] = PyQt4
PyQt4.QtWidgets = PyQt4.QtGui

However, If I add print sys at the end of Qt.py, sys equals None:

print sys
>>> None

Why does sys "break" and can I avoid breaking it?

This is in Python 2.7.11 on OS X.

---

@Lol4t0 – Here's an example where I'm only using standard modules:

# Xyz.py

import os
import sys

sys.modules['Xyz'] = os
print sys  # this will print "None"

So importing this will result in that "None is printed:

$ python
Python 2.7.11 (default, Jan 22 2016, 08:29:18)
[GCC 4.2.1 Compatible Apple LLVM 7.0.2 (clang-700.1.81)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import Xyz
None

Answer 1

When there are no longer any reference to a module, it will drop all its globals by replacing them with None.

You need to remember the old verion of sys.modules['Xyz'] (i.e. the current module) until you are done executing it.