What's the difference between '_io' and 'io'?

Question

I tried the code below. The f is of type _io.TextIOWrapper, but I cannot find any help info about this type. While there does exsist another similar type io.TextIOWrapper.

>>> f=open("c:\setup.log","r")
>>> type(f)
<class '_io.TextIOWrapper'>
>>> help(_io.TextIOWrapper)
Traceback (most recent call last):
  File "<pyshell#204>", line 1, in <module>
    help(_io.TextIOWrapper)
NameError: name '_io' is not defined
>>> help(io.TextIOWrapper)
Help on class TextIOWrapper in module io:

My questions are:

• If the name _io is not defined, how can I use it?

• What's the difference between _io and io modules?

Answer 1

The _io module provides the C code that the io module uses internally. The source for it can be found here. You can actually import both io and _io separately:

>>> import _io
>>> import io
>>> _io
<module 'io' (built-in)>  # The fact that this says io instead of _io is a bug (Issue 18602)
>>> io
<module 'io' from '/usr/lib/python3.4/io.py'>
>>> _io.TextIOWrapper
<type '_io.TextIOWrapper'>

This pattern (C-code for modulename provided in _modulename) is actually used for several modules - multiprocessing/_multiprocessing, csv/_csv, etc. Basically all cases where a module has a component that's written in C.