Why am I getting a \'TypeError: unhashable type: \'dict\'\' in Python and how can I fix it?

TypeError: unhashable type: 'dict'

This error occurs when you attempt to use a dictionary as a key in a dictionary or in a set. Pythons has consists of immutable objects (such as strings, integers, floats, frozensets, and tuples of immutables) are hashable and can serve as keys. However, dictionaries are mutable and hence not hashable.

To use a dictionary as a key, you must convert it into a hashable format. If the dictionary contains only immutable values, you can create a hashable representation of it using frozenset():

<code class="python">dict_key = {"a": "b"}
key = frozenset(dict_key.items())</code>

Now you can use key as a key in a dictionary or set:

<code class="python">some_dict[key] = True</code>

If the dictionary contains values that are themselves dictionaries or lists, you need to recursively convert them to hashable formats. Here's a utility function that can help:

<code class="python">def freeze(d):
    if isinstance(d, dict):
        return frozenset((key, freeze(value)) for key, value in d.items())
    elif isinstance(d, list):
        return tuple(freeze(value) for value in d)
    return d</code>

By using this function, you can freeze the dictionary and then use it as a key:

<code class="python">key = freeze(dict_key)
some_dict[key] = True</code>

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