New Iterables in Python 3.0

One of the fundamental changes in Python 3.0 is that it has a stronger emphasis on iterators than 2.X. In addition to the iterators associated with built-in types such as files and dictionaries, the dictionary methods keys, values, and items return iterable objects in Python 3.0, as do the built-in functions range, map, zip, and filter. As shown in the prior section, the last three of these functions both return iterators and process them. All of these tools produce results on demand in Python 3.0, instead of constructing result lists as they do in 2.6.

Although this saves memory space, it can impact your coding styles in some contexts. In various places in this book so far, for example, we’ve had to wrap up various function and method call results in a list(...) call in order to force them to produce all their results at once: