Question

Assume mydict is a Python dictionary.

mydict = {'a': 1, 'b': 2}

I can use items to iterate its elements:

for k,v in mydict.items():
    print k,v

Or use iteritems:

for k,v in mydict.iteritems():
    print k,v

what’s the difference? I think the philosophy of python is ‘only one way to do’?

Answer 1

In Python 3 the dict.iter...() methods have been removed and replace the normal ones.

They existed as iterators were added into the language after dictionaries, so dict.items() returns a list. The dict.iter...() methods were added to allow people to make more efficient programs (as iterators are lazy), but also not break compatibility with old programs that expected a list.

As Python 3 broke compatibility, this was fixed. (The old usage of dict.iter() can be generated with list(dict.iter()). Note that in Python 3 dict.items() actually returns a dictionary view – which can be iterated over, but also provides other functionality.