Accessing dict_keys element by index in Python3

150

I'm trying to access a dict_key's element by its index:

test = {'foo': 'bar', 'hello': 'world'}
keys = test.keys()  # dict_keys object

keys.index(0)
AttributeError: 'dict_keys' object has no attribute 'index'

I want to get foo.

same with:

keys[0]
TypeError: 'dict_keys' object does not support indexing

How can I do this?

This question is tagged with python dictionary python-3.x key

~ Asked on 2013-08-31 19:30:57

The Best Answer is


194

Call list() on the dictionary instead:

keys = list(test)

In Python 3, the dict.keys() method returns a dictionary view object, which acts as a set. Iterating over the dictionary directly also yields keys, so turning a dictionary into a list results in a list of all the keys:

>>> test = {'foo': 'bar', 'hello': 'world'}
>>> list(test)
['foo', 'hello']
>>> list(test)[0]
'foo'

~ Answered on 2013-08-31 19:33:10


67

Not a full answer but perhaps a useful hint. If it is really the first item you want*, then

next(iter(q))

is much faster than

list(q)[0]

for large dicts, since the whole thing doesn't have to be stored in memory.

For 10.000.000 items I found it to be almost 40.000 times faster.

*The first item in case of a dict being just a pseudo-random item before Python 3.6 (after that it's ordered in the standard implementation, although it's not advised to rely on it).

~ Answered on 2014-12-24 14:59:20


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