Get: TypeError: 'dict_values' object does not support indexing when using python 3.2.3

131
votes

This is my code:

{names[i]:d.values()[i] for i in range(len(names))}

This works completely fine when using python 2.7.3; however, when I use python 3.2.3, I get an error stating 'dict_values' object does not support indexing. How can I modify the code to make it compatible for 3.2.3?

3
pythonpython-3.x
values now returns a view object docs.python.org/3.2/library/… - dm03514
Why are you relying on the order of the values returned from a dictionary anyway? - David Robinson
Yeah, this code is unreliable unless d is an OrderedDict - and even if it is is seems like there must be a better way. - Peter DeGlopper
A case I use it in is when I know there is only one key value in the dict from say a database row retrieval for one column only in dict format per row. I think it is extremely poor that values() cannot auto_convert when indexed. - Samantha Atkins

3 Answers

209
votes

In Python 3, dict.values() (along with dict.keys() and dict.items()) returns a view, rather than a list. See the documentation here. You therefore need to wrap your call to dict.values() in a call to list like so:

v = list(d.values())
{names[i]:v[i] for i in range(len(names))}
17
votes

A simpler version of your code would be:

dict(zip(names, d.values()))

If you want to keep the same structure, you can change it to:

vlst = list(d.values())
{names[i]: vlst[i] for i in range(len(names))}

(You can just as easily put list(d.values()) inside the comprehension instead of vlst; it's just wasteful to do so since it would be re-generating the list every time).

9
votes

In Python 3 the dict.values() method returns a dictionary view object, not a list like it does in Python 2. Dictionary views have a length, can be iterated, and support membership testing, but don't support indexing.

To make your code work in both versions, you could use either of these:

{names[i]:value for i,value in enumerate(d.values())}

    or

values = list(d.values())
{name:values[i] for i,name in enumerate(names)}

By far the simplest, fastest way to do the same thing in either version would be:

dict(zip(names, d.values()))

Note however, that all of these methods will give you results that will vary depending on the actual contents of d. To overcome that, you may be able use an OrderedDict instead, which remembers the order that keys were first inserted into it, so you can count on the order of what is returned by the values() method.