Can a tuple be used as a dictionary key?

Frequently Asked Questions Python FAQ
1

Question

This exercise says a key can be a hashable type like a number or string. Can a tuple be used as a dictionary key?

Answer

Yes, a tuple is a hashable value and can be used as a dictionary key. A tuple would be useful as a key when storing values associated with a grid or some other coordinate type system. The following code example shows a dictionary with keys representing a simple x,y grid system.

coordinates = { (0,0) : 100, (1,1) : 200}
coordinates[(1,0)] = 150
coordinates[(0,1)] = 125

print(coordinates)
# {(0, 0): 100, (1, 1): 200, (1, 0): 150, (0, 1): 125}
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Am i correct in assuming that the value being calculated is based on the binary system?

That means when using a Tuple as key, the dictionary can actually calculate stuff… cool.

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3

No, you’re wrong
This example just shows that the author added some values manually to the dictionary by using tuples as keys of the values
Similar to .append() in lists

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Oh God i’m stupid, you’re correct. That was just a simple key-value assignment. Thanks for correcting me.

& welcome to the forums btw! :smiley:

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what if I have a dictionary like this :

my_dict = {(1,2): (12, 4), (3, 4): (13, 5), (5, 6): (14, 5)}

if I want to pair each value in the first tuple with the corresponding value in the second tuple, how would I do that?

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I tried it and it seems to work exactly as you typed it :+1:

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I’m wondering that, too .Is there anyone in here to show how to do that pairing?

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As the user above posted you already can create a dictionary like this so that your key:value pair is a tuple mapping to a particular value. Could you explain what other kind of pairing you have in mind?

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student_exam_result ={ (“Jane” , “Ashley”, “Celine”) : (80, 90, 65),
(“Tim”, “Emile”) : [65, 75) }
how can I reach just tim’s score. It’s what I meant when I’m saying pairing… Thank you for answering by the way.

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You’d first need to access the dictionary by key ("Tim", "Emile",) and then index the list or tuple you use next. So student_exam_result[("Tim", "Emile")][0] in this case. That would be a very unfortunate choice of nesting here, there is likely a much better way to organise such values if the use of this dictionary wass to get individual student scores back.

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It’s clear now. Thank you for your answer.

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Good Question, and the example demonstrates the power of a dictionary. ty

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If you look at what you’re asking, is that you want a mapping from (“Jane” , “Ashley”, “Celine”) to (80, 90, 65) so that Jane is associated with 80 etc. This is simply a dictionary! so instead the thing to do is {"Jane":80,"Ashley":90,"Celine":65}, which contains the much simpler and obvious mapping between name and score.

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What you are asking to do can be done many different ways using logic. Not the ‘right’ way to create dictionaries but can be done. I can think of a couple of other ways to do this but one of them is below. Meanwhile, since keys of a dictionary cannot be duplicated - if any of your values in each first tuple is a duplicate of another value which you are intending to use as a key - I have already made a provision for being able to give a new value. Of course, you could inadvertently enter a NEW value that is also a duplicate and that will require more logic to handle - which I have not written. Hopefully, this piece of code will suffice.

codacademyforumsreply1dict
codacademyforumsreply1dict1552×634 80.7 KB

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15

A lot of things to learn here. Here’s another simple example that could help to get things more clear about using a tuple as a key in a Python dictionary :

coordinates_info = {}

Defining a tuple representing coordinates (latitude, longitude)

location_1 = (34.0522, -118.2437)
coordinates_info[location_1] = “Los Angeles”

Adding another location

location_2 = (40.7128, -74.0060)
coordinates_info[location_2] = “New York City”

print(coordinates_info)

{(34.0522, -118.2437): ‘Los Angeles’, (40.7128, -74.0060): ‘New York City’}

1 Like