Extending Pylint

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Writing your own checker

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You can find some simple examples in the examples directory of the

distribution (custom.py and custom_raw.py). I'll try to quickly

explain the essentials here.

First, there are two kinds of checkers:

* raw checkers, which are analysing each module as a raw file stream

* ast checkers, which are working on an ast representation of the

module

The ast representation used is an extension of the one provided with

the standard Python distribution in the ast package. The extension

adds additional information and methods on the tree nodes to ease

navigation and code introspection.

An AST checker is a visitor, and should implement *visit_<lowered

class name>* or *leave_<lowered class name>* methods for the nodes

it's interested in. To get description of the different classes used

in an ast tree, look at the ast package documentation. Checkers are

ordered by priority. For each module, Pylint's engine:

1. give the module source file as a stream to raw checkers

2. get an ast representation for the module

3. make a depth first descent of the tree, calling "visit_<>" on

each AST checker when entering a node, and "leave_<>" on the back

traversal

Notice that the source code is probably the best source of

documentation, it should be clear and well documented. Don't hesitate

to ask for any information on the code-quality mailing list.