Difference between a loaded module and an initialized module?

Question

In the reference manual it is stated that:

A complete Python program is executed in a minimally initialized environment: all built-in and standard modules are available, but none have been initialized, except for sys (various system services), builtins (built-in functions, exceptions and None) and __main__.

I am uncertain about what "initialized" is supposed to mean here. I always thought that a module was initialized if it was loaded and present in sys.modules:

This is a dictionary that maps module names to modules which have already been loaded.

Apparently, I was wrong because sys.modules contains many other modules:

python -c "import sys; print(sys.modules.keys() - {'sys', 'builtins', '__main__'})"
{'_stat', 'encodings.aliases', '_sitebuiltins', '_thread', 'io', '_weakrefset', 'genericpath', 'encodings.utf_8', 'codecs', 'os', '_weakref', '_codecs', '_frozen_importlib', '_io', '_frozen_importlib_external', 'os.path', '_warnings', '_bootlocale', '_signal', 'errno', '_imp', 'encodings.latin_1', 'sysconfig', 'marshal', 'encodings', 'usercustomize', 'site', 'posixpath', '_collections_abc', 'posix', '_sysconfigdata_m_linux_x86_64-linux-gnu', 'encodings.cp437', 'abc', 'zipimport', 'stat', '_locale'}

What is the difference between an initialized and a loaded module? I'm on Python 3.

Answer 1

The language initialization has gotten a lot more complicated since that documentation was written. (It's been mostly unchanged since at least Python 1.4.) All those modules in sys.modules are fully loaded and initialized.