How to Solve Python TypeError: ‘dict_keys’ object is not subscriptable

by | Programming, Python, Tips

In Python, you cannot access values inside a dict_keys object using indexing syntax.

A dict_keys object is a dynamic view object that displays all the keys in the dictionary.

You can solve this error by converting the dict_keys object to a list object using the built-in list() method. For example,

my_dict = {'particle':'electron', 'mass':0.511, 'charge': -1}
keys = list(my_dict.keys())
particle = keys[0]

This tutorial will detail the error and how to solve it with code examples.


TypeError: ‘dict_keys’ object is not subscriptable

Let’s break up the error message to understand what the error means. TypeError occurs whenever you attempt to use an illegal operation for a specific data type. The part “dict_keys object” tells us the error concerns an illegal operation for the view object returned by the dictionary keys() method.

The part “is not subscriptable” tells us we cannot access an element of the dict_keys object using the subscript operator, which is square brackets [].

A subscriptable object is a container for other objects and implements the __getitem__() method. Examples of subscriptable objects include strings, lists, tuples, and dictionaries.

We can check if an object implements the __getitem__() method by listing its attributes with the dir function. Let’s call the dir function and pass a dict_keys object and a str object to see their attributes.

my_dict = {'fruit':'apple', 'in_stock':True, 'amount': 46}
keys = my_dict.keys()
print(dir(keys))
['__and__', '__class__', '__contains__', '__delattr__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__iter__', '__le__', '__len__', '__lt__', '__ne__', '__new__', '__or__', '__rand__', '__reduce__', '__reduce_ex__', '__repr__', '__reversed__', '__ror__', '__rsub__', '__rxor__', '__setattr__', '__sizeof__', '__str__', '__sub__', '__subclasshook__', '__xor__', 'isdisjoint']

We can see that __getitem__ is not present in the list of attributes for the dict_keys object.

string = "Python"
print(dir(string))
['__add__', '__class__', '__contains__', '__delattr__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__getitem__', '__getnewargs__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__iter__', '__le__', '__len__', '__lt__', '__mod__', '__mul__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__rmod__', '__rmul__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', 'capitalize', 'casefold', 'center', 'count', 'encode', 'endswith', 'expandtabs', 'find', 'format', 'format_map', 'index', 'isalnum', 'isalpha', 'isascii', 'isdecimal', 'isdigit', 'isidentifier', 'islower', 'isnumeric', 'isprintable', 'isspace', 'istitle', 'isupper', 'join', 'ljust', 'lower', 'lstrip', 'maketrans', 'partition', 'replace', 'rfind', 'rindex', 'rjust', 'rpartition', 'rsplit', 'rstrip', 'split', 'splitlines', 'startswith', 'strip', 'swapcase', 'title', 'translate', 'upper', 'zfill']

We can see that __getitem__ is present in the list of attributes for the str object.

If you want to check if a specific attribute belongs to an object, you can check for membership using the in operator. This approach is easier than looking through the list of attributes by eye.

my_dict = {'fruit':'apple', 'in_stock':True, 'amount': 46}
keys = my_dict.keys()
# Check type of object
print(type(keys))
# Check membership of attribute
print('__getitem__' in dir(keys))
<class 'dict_keys'>
False

We can see that __getitem__ is not an attribute of the dict_keys class.

string = "Python"
print(type(string))
print('__getitem__' in dir(string))
<class 'str'>
True

We can see that __getitem__ is an attribute of the str class.

Example

Let’s look at an example of trying to index a dict_keys object. First, we will create the dictionary.

my_dict = {'name':'vincent', 'age':27, 'profession': 'artist'}

Then we will call the keys() method on the dictionary, which returns a dictionary view object that displays all the keys in the dictionary. The view object changes when the dictionary changes.

keys = my_dict.keys()
print(type(keys))
<class 'dict_keys'>

Next, we will try to access the first key in the dict_keys object using the subscript operator [].

first_key = keys[0]
print(first_key)

Let’s run the code to see what happens:

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
Input In [8], in <cell line: 1>()
----> 1 first_key = keys[0]
      2 print(first_key)

TypeError: 'dict_keys' object is not subscriptable

The error occurs because we are trying to access the first key using indexing, which is not possible with dict_keys objects.

Solution

We can solve this error by converting the dict_keys object to a list using the built-in list() method. Let’s look at the revised code:

my_dict = {'name':'vincent', 'age':27, 'profession': 'artist'}
keys = list(my_dict.keys())
print(type(keys))
first_key = keys[0]
print(first_key)

Let’s run the code to get the first key:

<class 'list'>
name

Summary

Congratulations on reading to the end of this tutorial!

For further reading on AttributeErrors, go to the articles:

To learn more about Python for data science and machine learning, you can go to the online courses page on Python for the most comprehensive courses.

Have fun and happy researching!

Research Scientist at Moogsoft | + posts

Suf is a research scientist at Moogsoft, specializing in Natural Language Processing and Complex Networks. Previously he was a Postdoctoral Research Fellow in Data Science working on adaptations of cutting-edge physics analysis techniques to data-intensive problems in industry. In another life, he was an experimental particle physicist working on the ATLAS Experiment of the Large Hadron Collider. His passion is to share his experience as an academic moving into industry while continuing to pursue research. Find out more about the creator of the Research Scientist Pod here and sign up to the mailing list here!