Comparisons in Python 2.6 use specific methods such as __lt__ for less than if present, or else the general __cmp__. Python 3.0 uses only specific methods, not __cmp__, as discussed later in this chapter.

Boolean tests similarly try a specific __bool__ first (to give an explicit True/False result), and if it’s absent fall back on the more general __len__ (a nonzero length means True). As we’ll also see later in this chapter, Python 2.6 works the same but uses the name __nonzero__ instead of __bool__.