Can you use a tuple as a dictionary key? Well, that depends.

Today I was asked if you can use a tuple as a dictionary key. I wasn't sure, and looked into it. And the answer seems to be, 'it depends'.

Can you ever use a tuple as a dictionary key? Yes:


In [35]: my_tup = (1, 2)

In [36]: my_dict = {my_tup: 1}

In [37]: my_dict
Out[37]: {(1, 2): 1}

Can you ALWAYS use a tuple as a dictionary key? Nope:

In [38]: my_other_tup = ([1, 2], 2)

In [39]: my_dict = {my_other_tup: 2}
------------------------------------------------------------
TypeError                 Traceback (most recent call last)
<ipython-input...> in <module>()
----> 1 my_dict = {my_other_tup: 2}

TypeError: unhashable type: 'list'

You can use a tuple as a dictionary key, but only if it's hashable all the way down.