Question

Is it legitimate to use items() instead of iteritems() in all places? Why was iteritems() removed from Python 3? Seems like a terrific and useful method. What’s the reasoning behind it?

Edit: To clarify, I want to know what is the correct idiom for iterating over a dictionary in a generator-like way (one item at a time, not all into memory) in a way that is compatible with both Python 2 and Python 3?

Answer 1

In Python 2.x – .items() returned a list of (key, value) pairs. In Python 3.x, .items() is now an itemview object, which behaves differently – so it has to be iterated over, or materialised… So, list(dict.items()) is required for what was dict.items() in Python 2.x.

Python 2.7 also has a bit of a back-port for key handling, in that you have viewkeys, viewitems and viewvalues methods, the most useful being viewkeys which behaves more like a set (which you’d expect from a dict).

Simple example:

common_keys = list(dict_a.viewkeys() & dict_b.viewkeys())

Will give you a list of the common keys, but again, in Python 3.x – just use .keys() instead.

Python 3.x has generally been made to be more "lazy" – i.e. map is now effectively itertools.imap, zip is itertools.izip, etc.