This is copied verbatim from the old IPython wiki and is currently under development. Much of the information in this part of the development guide is out of date.
This document describes our coding style. Coding style refers to the
How source code is formatted (indentation, spacing, etc.)
How things are named (variables, functions, classes, modules, etc.)
In general, we follow the standard Python style conventions as described
in Python’s PEP 8, the
official Python Style Guide.
Other general comments:
In a large file, top level classes and functions should be separated
by 2 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.
For naming conventions, we also follow the guidelines of PEP
8. Some of the existing
code doesn’t honor this perfectly, but for all new and refactored
IPython code, we’ll use:
All lowercase module names. Long module names can have words
separated by underscores (really_long_module_name.py), but this
is not required. Try to use the convention of nearby files.
CamelCase for class names.
lowercase_with_underscores for methods, functions, variables and
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 of ip. This is not necessary and
all new code should not use this prefix. The only case where this
approach is justified is for classes or functions which are expected
to be imported into external namespaces and a very generic name (like
Shell) that is likely to clash with something else. However, if a
prefix seems absolutely necessary the more specific IPY or
ipy are preferred.
In general, objects should declare, in their class, all attributes the
object is meant to hold throughout its life. While Python allows you to
add an attribute to an instance at any point in time, this makes the
code harder to read and requires methods to constantly use checks with
hasattr() or try/except calls. By declaring all attributes of the object
in the class header, there is a single place one can refer to for
understanding the object’s data interface, where comments can explain
the role of each variable and when possible, sensible defaults can be
If an attribute is meant to contain a mutable object, it should be set
to None in the class and its mutable value should be set in the
object’s constructor. Since class attributes are shared by all
instances, failure to do this can lead to difficult to track bugs. But
you should still set it in the class declaration so the interface
specification is complete and documented in one place.
A simple example:
# X does..., sensible default given:
x = 1
# y does..., default will be set by constructor
y = None
# z starts as an empty list, must be set in constructor
z = None
def __init__(self, y):
self.y = y
self.z = 
When starting a new Python file for IPython, you can use the following
template as a starting point that has a few common
things pre-written for you.