What is "_csv" in Python?

Question

In attempting to read the source code for the csv.py file (as a guide to implementing my own writer class in another context) I found that much of the functionality in that file is, in turn, imported from something called _csv:

 from _csv import Error, __version__, writer, reader, register_dialect, \
                  unregister_dialect, get_dialect, list_dialects, \
                  field_size_limit, \
                  QUOTE_MINIMAL, QUOTE_ALL, QUOTE_NONNUMERIC, QUOTE_NONE, \
                  __doc__

I cannot find any file with this name on my system (including searching for files with the Hidden attribute set), although I can do import _csv from the Python shell.

What is this module and is it possible to read it?

Answer 1

_csv is the C "backbone" of the csv module. Its source is in Modules/_csv.c. You can find the compiled version of this module from the Python command prompt with:

>>> import _csv
>>> _csv
<module '_csv' from '/usr/lib/python2.6/lib-dynload/_csv.so'>

There are no hidden files in the Python source code :)

Answer 2

Not to disagree with larsmans answer.

There is an official explanation of the module naming convention in PEP8:

When an extension module written in C or C++ has an accompanying Python module that provides a higher level (e.g. more object oriented) interface, the C/C++ module has a leading underscore (e.g. _socket)