It says on http://www.python.org/dev/peps/pep-0008/
Package and Module Names
Modules should have short, all-lowercase names. Underscores can be used
in the module name if it improves readability. Python packages should
also have short, all-lowercase names, although the use of underscores is
discouraged.
But StringIO does not following this convention. Although on the same
page, it also mentions the following. However, since StringIO is in
the library, shall its name be rectified?
The naming conventions of Python's library are a bit of a mess, so we'll
never get this completely consistent -- nevertheless, here are the
currently recommended naming standards. New modules and packages
(including third party frameworks) should be written to these standards,
but where an existing library has a different style, internal consistency
is preferred.
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