在Python的字典的前半部分迭代

Question

How to iterate over first half of dictionary in python

This iterates over all values in the dictionary

for key, value in checkbox_dict.iteritems():
    print key,value

But I want to iterate over the first half of the dictionary only.

one way is to do it like this

for key, value in dict(checkbox_dict.items()[:11]).iteritems():
    print key,value

Is there any better way also ?

Answer 1

If you mean: over half of the items here's a way:

for key, value in checkbox_dict.items()[:int(len(checkbox_dict)/2)]:
    pass

… But be aware: the elements in a normal dictionary don't necessarily keep the same iteration order that was used for inserting the elements … unless you use an OrderedDict .

Answer 2

You can use itertools.islice to slice the dict.iteritems iterator, unlike dict.items() with slice this won't create an intermediate list in memory.

>>> from itertools import islice
>>> d = dict.fromkeys('abcdefgh')
>>> for k, v in islice(d.iteritems(), len(d)/2):
    print k, v
...     
a None
c None
b None
e None

Note that normal dictionaries are unordered, so the items are returned in arbitrary order.