When should iteritems() be used instead of items()?
Solution 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 different - 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.
Solution 2:
dict.iteritems
was removed because dict.items
now does the thing dict.iteritems
did in python 2.x and even improved it a bit by making it an itemview
.
Solution 3:
The six library helps with writing code that is compatible with both python 2.5+ and python 3. It has an iteritems method that will work in both python 2 and 3. Example:
import six
d = dict( foo=1, bar=2 )
for k, v in six.iteritems(d):
print(k, v)
Solution 4:
As the dictionary documentation for python 2 and python 3 would tell you, in python 2 items
returns a list, while iteritems
returns a iterator.
In python 3, items
returns a view, which is pretty much the same as an iterator.
If you are using python 2, you may want to user iteritems
if you are dealing with large dictionaries and all you want to do is iterate over the items (not necessarily copy them to a list)