How to solve TypeError:unhashable type:'dict' error in Python

Python "TypeError: unhashable type: ‘dict’ " occurs when we use a dictionary as a key in another dictionary or as an element in a collection.

To resolve this error, you need to use frozenset instead, or convert the dictionary to a JSON string before using it as a key.

The error occurs when we use a dictionary as a key in another dictionary.

# ????️ using dictionary as a key in a dictionary

# ⛔️ TypeError: unhashable type: 'dict'
my_dict = {'name': 'Jiyik', {'country': 'China'}: 'address'}

Or when we use a dictionary as an element in a set object.

# ????️ 使用字典作为集合中的元素

# ⛔️ TypeError: unhashable type: 'dict'
my_set = {{'name': 'Jiyik'}}

We cannot use a dictionary as a key in a dictionary or an element in a collection because dictionary objects are mutable and unhashable.

Convert the dictionary to a JSON string to resolve the error

One way to resolve this error is to convert the dictionary to a JSON string before using it as a key.

import json

# ????️ 将字典转换为 JSON 字符串
my_json = json.dumps({'country': 'China'})

my_dict = {'name': 'Jiyik', my_json: 'address'}
print(my_dict)  # ????️ {'name': 'Jiyik', '{"country": "China"}': 'address'}

# ????️ 当你必须访问字典中的键时
print(my_dict[json.dumps({'country': 'Austria'})]) # ????️ address

json.dumps Method converts a Python object into a JSON-formatted string. This works because strings are immutable and hashable.

In contrast, the json.loads method parses a JSON string into a native Python object, such as my_dict = json.loads(my_json_str).

Using frozenset to resolve errors

Another way to resolve errors is to use frozenset.

my_key = {'country': 'China'}
key = frozenset(my_key.items())
print(key)  # ????️ frozenset({('country', 'China')})

my_dict = {'name': 'Jiyik', key: 'address'}


# ????️ 当我们必须访问 key 时
print(my_dict[frozenset(my_key.items())])  # ????️ 'address'

dict.items Method returns a new view of dictionary items ((key, value) pairs).

# ????️ dict_items([('name', 'jiyik'), ('age', 30)])
print({'name': 'jiyik', 'age': 30}.items())

We use the dictionary's items to create a frozenset that we can use as a key in the dictionary (as well as an element in another set).

frozenset is an immutable version of a Python collection object, so it can be used as a key in a dictionary or as an element in another collection.

Please note that we must use the same method to access the keys in the dictionary.

We can store the result of calling frozenset(my_key.items()) in a variable and reuse the frozenset when setting or accessing keys in the dictionary.

Convert dictionary to tuple to resolve error

Another way to resolve the error is to convert dictionary to tuple.

dict_key = {'id': 1, 'country': 'China'}

# ✅ 转换为元组
my_tuple = tuple(dict_key)
print(my_tuple)  # ????️ ('id', 'country')

my_dict = {'name': 'Jiyik', my_tuple: 'address'}
print(my_dict)  # ????️ {'name': 'Jiyik', ('id', 'country'): 'address'}

# ????️ 当你必须访问字典中的键时
print(my_dict[my_tuple])  # ????️ address

When converting a dictionary to a tuple, the tuple only contains the keys of the dictionary.

Tuples are immutable, so a tuple containing a dictionary key can safely be used as a key in another dictionary.

Using one dictionary as a value in another dictionary

We cannot use a dictionary as a key in another dictionary, but we can use a dictionary as a value.

dict_value = {'id': 1, 'country': 'China'}

my_dict = {'name': 'Jiyik', 'data': dict_value}

# ????️ {'name': 'Jiyik', 'data': {'id': 1, 'country': 'China'}}
print(my_dict)

print(my_dict['data'])  # ????️ {'id': 1, 'country': 'China'}

We set a dictionary to a value in another dictionary.

This is allowed because the limit does not apply to dictionary values.

Add all key-value pairs of one dictionary to another dictionary

If you need to add all key-value pairs of one dictionary to another dictionary, you can use a for loop.

another_dict = {'id': 1, 'country': 'China'}

my_dict = {'name': 'Jiyik'}

for key, value in another_dict.items():
    my_dict[key] = value

# ????️ {'name': 'Jiyik', 'id': 1, 'country': 'China'}
print(my_dict)

dict.items Method returns a new view of dictionary items ((key, value) pairs).

my_dict = {'id': 1,  'name': 'Jiyik'}

# ????️ dict_items([('id', 1), ('name', 'Jiyik')])
print(my_dict.items())

In each iteration, we set the key-value pairs to another dictionary.

Hashable vs. Unhashable Objects in Python

Most of the immutable built-in objects in Python are hashable, while mutable objects are not hashable.

If an object is hashable, then it can be used as a key in a dictionary and an element in a collection because these data structures use hash values ​​internally.

Hashable objects include - str, int, bool, tuple, frozenset.

Unhashable objects include - list, dict, set.

Please note that tuples and frozen sets are hashable only if their elements are hashable.

Checking if an object is hashable

We can check if an object is hashable by passing it to the built-in

hash()

function.

print(hash('jiyik.com'))  # ????️ 4905958875846995527

# ⛔️ TypeError: unhashable type: 'dict'
print(hash({'name': 'Jiyik'}))

The hash function returns the hash value of the passed in object (if any).

Hash values ​​are integers used to compare dictionary keys during dictionary lookups.

!> The hash value of a hashable object never changes during its lifetime. This is why most immutable objects are hashable, while mutable objects are not hashable.

Objects like dictionaries are mutable because the contents of the dictionary can change.

my_dict = {'name': 'Fql'}

my_dict['name'] = 'Jiyik'

print(my_dict) # ????️ {'name': 'Jiyik'}

On the other hand,

fronzenset

and tuple objects containing primitive values ​​are immutable (and hashable). Dictionaries are indexed by keys, which can be any immutable type, such as strings or numbers.

Tuples can only be used as keys in a dictionary if they contain strings, numbers, or tuples.

If the

fronzenset

or tuple contains a mutable object (such as a list), it cannot be used as a key in a dictionary or an element in a set. If we are not sure what type of object a variable stores, please use the

type()

function.

my_dict = {'name': 'Jiyik'}

print(type(my_dict))  # ????️ 
print(isinstance(my_dict, dict))  # ????️ True

my_str = 'jiyik.com'

print(type(my_str))  # ????️ 
print(isinstance(my_str, str))  # ????️ True

type

The function returns the type of the object.

If the object passed in is an instance or subclass of the passed class, the isinstance function returns True.

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