Can an empty key be used to insert a value into a dictionary?

Frequently Asked Questions Python FAQ
1

Question

Is it possible to accidentally insert a key into a dictionary which doesn’t have any meaning?

Answer

Just because a key doesn’t have a useful meaning, it can still be inserted into a dictionary as long as Python is able to compute a hash value for it. The following code example shows three keys which Python will accept without reporting an error. These keys are unlikely to be useful but are accepted by Python without complaint and could result in unexpected behavior.

mydict = {}

mykey = None
mydict[mykey] = 100

mykey = ''
mydict[mykey] = 200

mykey = False
mydict[mykey] = 300

print(mydict)
# {None: 100, '': 200, False: 300}
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Also we can replace a value of a key?

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Hello @blog1798493321!

Yes, we can overwrite a key’s value using my_dict["key_name"] = new_value.

This topic is covered in this lesson.

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4

Yup, but not the key itself.

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5

Yes not the key only the value. We can delete the key.

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6

By this way, won’t it make a new key:value pair?

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No. All keys in a Python dictionary must be unique, meaning there is always only one instance of that key in the dictionary. Therefore, when we use my_dict["key_name"] = new_value, we are overwriting the value of that specific key.

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8

Can an empty key be used to insert a value into a dictionary?

No, an empty key cannot be used to insert a value into a dictionary in Python. Dictionary keys must be unique and hashable. An empty key does not meet these requirements because it is not a valid key.

In Python, dictionary keys can be of any hashable data type such as strings, numbers, tuples, or other immutable types. However, an empty key has no value or identity to serve as a unique identifier, so it cannot be used as a dictionary key.

If you attempt to use an empty key, you will encounter a TypeError indicating that the key is unhashable.

That is chatGPT said. So the answers at the beginning should be wrong and no one is checking it.

9

In the case you provided, None is not an empty key. It is a valid key that represents the value 100 in the dictionary mydict.

An empty key refers to a key that has an empty value, such as an empty string ''. In your example, you used None, '' (empty string), and False as keys with corresponding values 100, 200, and 300 respectively. None of these keys are considered empty keys because they have non-empty values associated with them.

So, in your dictionary mydict, {None: 100, '': 200, False: 300}, None is not an empty key. It is a valid key with a non-empty value.

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