How to Make Mistakes in Python by Mike Pirnat

Author:Mike Pirnat
Language: eng
Format: mobi, epub, pdf
Publisher: O'Reilly Media, Inc.
Published: 2015-10-02T04:00:00+00:00

God Objects and God Methods

A well-behaved class or method should have a strictly limited set of responsibilities, preferably as close to one as possible (in accordance with the Single Responsibility Principle), and should only contain whatever knowledge or data it needs to fulfill its limited role. All classes and methods start this way, simple and innocent, but we may find it convenient or expedient to grow these entities as our requirements evolve. When a class or method has accumulated too much knowledge or too many responsibilities, its role in the system becomes practically godlike: it has become all-encompassing, all-seeing, and all-doing, and many other entities will end up being tightly coupled to it in order to get anything done. Like big banks in the autumn of 2008, our god objects and god methods are too big to maintain, yet too big to fail.

These are pretty easy to spot: we’re looking for large modules, large classes, classes with many methods, and long methods or functions. There are a couple of different ways to go about this.

Pylint will by default complain about modules longer than 1000 lines and functions longer than 50 lines (and you can adjust these values as needed), but you have to look carefully at its voluminous output to make sure you don’t miss these warnings. WingIDE and Komodo integrate with Pylint for code inspection, so they’ll also help you find these problems. Curiously, while PyCharm offers code inspection that covers many of the same issues that Pylint does, it doesn’t include warnings about module or function length.

If you aren’t someone who enjoys working with an IDE, you can use some Unix command-line kung fu to identify potential sources of godlike trouble:

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