以值作为列表遍历字典

Question

I've a dictionary 'mydict'.

{   'a': ['xyz1', 'xyz2'],
    'b': ['xyz3', 'xyz4'],
    'c': ['xyz5'],
    'd': ['xyz6']}

I'm trying to print out all the keys and values of this dictionary using the following code:

for username, details in mydict.iteritems():
    pprint.pprint(username + " " + details)

But, I'm getting the following error:

AttributeError: 'list' object has no attribute 'iteritems'

Any help would be appreciated.

Answer 1

This code works on your example

>>> import pprint
>>> mydict = {   'a': ['xyz1', 'xyz2'],
    'b': ['xyz3', 'xyz4'],
    'c': ['xyz5'],
    'd': ['xyz6']}

>>> for username, details in mydict.iteritems():
        pprint.pprint((username, details))


('a', ['xyz1', 'xyz2'])
('c', ['xyz5'])
('b', ['xyz3', 'xyz4'])
('d', ['xyz6'])

Answer 2

I get the same AttributeError when I attempt the original, this arrises becuase the VALUE in each KEY, VALUE pair is a list.

Using mydict.items() you can create a copy of each (KEY, VALUE) pair, which you can then print:

for key, value in mydict.items():
    print((key, value))

Though of course, creating a copy using items() is memory expensive if your dictionary is large. Which, is the big advantage (lower memory cost, more efficient AND * optimised for python *) of being able to use iteritems() to iterate through your dictionary.

Equally well, you could do the following:

for key in d:
    print((k, mydic[key]))

BUT (in python), this is slower again! Because you have to re-hash the dictionary each time as you look up mydict[key] . So, it seems that mydict.items() is the best option here, as it gives you access to the values directly through tuple unpacking.

Raymond Hettinger (the iteritems and generator guru from Python) gave a great talk at US PyCon, which you can watch here: http://pyvideo.org/video/1780/transforming-code-into-beautiful-idiomatic-pytho