Python by contract: a zero-defect approach

The idea of zero-defect development addresses quality issues by seeking to prevent the initial introduction of defects into a design, rather than trying to find and repair them later.

Cleanroom software engineering is a zero-defect methodology developed by IBM Federal Systems Division for use in the project that developed onboard software for the Space Shuttle.

The author learned the method from Dr. Allan M. Stavely, whose book Toward Zero-defect Programming describes the method in general. This work describes how the author has applied this methodology to the construction of programs in the Python programming language.

The term “cleanroom” is an analogy to the cleanrooms used in integrated circuit fabrication: it is better to write the code without defects than to try to find and remove them later.