module name in sys.modules and globals()

Question

If I import a module, the module name shows up in both sys.modules and globals(). If I again delete it, it is removed from globals(), but still resides in sys.modules. Why is it so?

import mymodule
'mymodule' in globals()   # True
'mymodule' in sys.modules # True
del mymodule
'mymodule' in globals()   # False
'mymodule' in sys.modules # Still True, why?

I also found the following difference:

from mypackage import mymodule
'mypackage' in sys.modules            # True
'mymodule'  in sys.modules            # False !
'mypackage.mymodule' in sys.modules   # also True !

while the answers are complementary for globals():

'mypackage' in sys.modules            # False
'mymodule'  in sys.modules            # True 
'mypackage.mymodule' in sys.modules   # False

Answer 1

Just like any other Python object, a module continues to exist until there are no more references to it. In other words, sys.modules behaves like a regular dict, and

import mymodule
lst = {mymodule.__name__: mymodule}
'mymodule' in globals()   # True
'mymodule' in lst         # True
del mymodule
'mymodule' in globals()   # False
'mymodule' in lst         # Still True

sys.modules is only consulted on import statements. You can delete a module from sys.modules to make Python reload it the next time it is imported.

Answer 2

del removes the binding of a name in the appropriate scope; it has nothing to do with modules per se.

sys.modules keeps a list of all modules that have been loaded, regardless of whether they're bound to any name in your program.