docs/source/development/coding_guide.txt

==============
 Coding guide
==============


Coding conventions
==================

In general, we'll try to follow the standard Python style conventions as
described in Python's `PEP 8`_, the official Python Style Guide.

.. _PEP 8: http://www.python.org/peps/pep-0008.html

Other comments:

- In a large file, top level classes and functions should be separated by 2-3
  lines to make it easier to separate them visually.

- Use 4 spaces for indentation, *never* use hard tabs.

- Keep the ordering of methods the same in classes that have the same methods.
  This is particularly true for classes that implement similar interfaces and
  for interfaces that are similar.

Naming conventions
------------------

In terms of naming conventions, we'll follow the guidelines of PEP 8.  Some of
the existing code doesn't honor this perfectly, but for all new IPython code
(and much existing code is being refactored), we'll use:

- All ``lowercase`` module names.

- ``CamelCase`` for class names.

- ``lowercase_with_underscores`` for methods, functions, variables and
  attributes.

This may be confusing as some of the existing codebase uses a different
convention (``lowerCamelCase`` for methods and attributes).  Slowly, we will
move IPython over to the new convention, providing shadow names for backward
compatibility in public interfaces.

There are, however, some important exceptions to these rules.  In some cases,
IPython code will interface with packages (Twisted, Wx, Qt) that use other
conventions.  At some level this makes it impossible to adhere to our own
standards at all times.  In particular, when subclassing classes that use other
naming conventions, you must follow their naming conventions.  To deal with
cases like this, we propose the following policy:

- If you are subclassing a class that uses different conventions, use its
  naming conventions throughout your subclass.  Thus, if you are creating a
  Twisted Protocol class, used Twisted's
  ``namingSchemeForMethodsAndAttributes.``

- All IPython's official interfaces should use our conventions.  In some cases
  this will mean that you need to provide shadow names (first implement
  ``fooBar`` and then ``foo_bar = fooBar``).  We want to avoid this at all
  costs, but it will probably be necessary at times.  But, please use this
  sparingly!

Implementation-specific *private* methods will use
``_single_underscore_prefix``.  Names with a leading double underscore will
*only* be used in special cases, as they makes subclassing difficult (such
names are not easily seen by child classes).

Occasionally some run-in lowercase names are used, but mostly for very short
names or where we are implementing methods very similar to existing ones in a
base class (like ``runlines()`` where ``runsource()`` and ``runcode()`` had
established precedent).

The old IPython codebase has a big mix of classes and modules prefixed with an
explicit ``IP``. In Python this is mostly unnecessary, redundant and frowned
upon, as namespaces offer cleaner prefixing. The only case where this approach
is justified is for classes which are expected to be imported into external
namespaces and a very generic name (like Shell) is too likely to clash with
something else.  We'll need to revisit this issue as we clean up and refactor
the code, but in general we should remove as many unnecessary ``IP``/``ip``
prefixes as possible. However, if a prefix seems absolutely necessary the more
specific ``IPY`` or ``ipy`` are preferred.

Older material
==============

General
-------

In general, we'll try to follow the standard Python style conventions as
described here:

* `Style Guide for Python Code  <http://www.python.org/peps/pep-0008.html>`_  


Other comments:

* In a large file, top level classes and functions should be 
  separated by 2-3 lines to make it easier to separate them visually.
* Use 4 spaces for indentation.
* Keep the ordering of methods the same in classes that have the same 
  methods.  This is particularly true for classes that implement an interface.

Naming conventions
------------------

In terms of naming conventions, we'll follow the guidelines from the `Style
Guide for Python Code`_.

For all new IPython code (and much existing code is being refactored), we'll
use:

* All ``lowercase`` module names.

* ``CamelCase`` for class names.

* ``lowercase_with_underscores`` for methods, functions, variables and
  attributes.

There are, however, some important exceptions to these rules. In some cases,
IPython code will interface with packages (Twisted, Wx, Qt) that use other
conventions. At some level this makes it impossible to adhere to our own
standards at all times. In particular, when subclassing classes that use other
naming conventions, you must follow their naming conventions. To deal with
cases like this, we propose the following policy:

* If you are subclassing a class that uses different conventions, use its
  naming conventions throughout your subclass.  Thus, if you are creating a
  Twisted Protocol class, used Twisted's
  ``namingSchemeForMethodsAndAttributes.``

* All IPython's official interfaces should use our conventions.  In some cases
  this will mean that you need to provide shadow names (first implement
  ``fooBar`` and then ``foo_bar = fooBar``).  We want to avoid this at all
  costs, but it will probably be necessary at times.  But, please use this
  sparingly!

Implementation-specific *private* methods will use
``_single_underscore_prefix``. Names with a leading double underscore will
*only* be used in special cases, as they makes subclassing difficult (such
names are not easily seen by child classes).

Occasionally some run-in lowercase names are used, but mostly for very short
names or where we are implementing methods very similar to existing ones in a
base class (like ``runlines()`` where ``runsource()`` and ``runcode()`` had
established precedent).

The old IPython codebase has a big mix of classes and modules prefixed with an
explicit ``IP``. In Python this is mostly unnecessary, redundant and frowned
upon, as namespaces offer cleaner prefixing. The only case where this approach
is justified is for classes which are expected to be imported into external
namespaces and a very generic name (like Shell) is too likely to clash with
something else. We'll need to revisit this issue as we clean up and refactor
the code, but in general we should remove as many unnecessary ``IP``/``ip``
prefixes as possible. However, if a prefix seems absolutely necessary the more
specific ``IPY`` or ``ipy`` are preferred.