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Python Python Collections (Retired) Dictionaries Teacher Stats

Posted by Andrew Ge
Andrew Ge
2,158 Points

Obtaining Unknown Dictionary Elements

How do I get the first key of a dictionary, if I don't know what's in the dictionary?

Here's my code, where I assumed that "Kenneth Love" would be a key.

Even though I used this method, I think it should have worked...?

1 Answer

Nathan Tallack
Nathan Tallack
22,159 Points
Nathan Tallack
Nathan Tallack
22,159 Points

Dictionaries are unordered by default (there is a ordered dictionary type but you are not learning that here).

So there is no "first" key as such.

What you can do is get a list of keys via the keys method. If your dictionary is named my_dict you could get a list of keys via my_dict.keys() which returns a list. You could iterate over that list.

Something like this.

my_dict = { "title1": "book1", "title2": "book2", "title3": "book3" }
for key in my_dict.keys():
    print(my_dict[key])

That would result in this output.

book2
book1
book3

Remember, unordered. :)

Andrew Ge
Andrew Ge
2,158 Points

Thank you!

Chris Freeman
Chris Freeman
Treehouse Moderator 68,423 Points
Chris Freeman
Chris Freeman
Treehouse Moderator 68,423 Points

Additionally, when a dict is used in a iterator context like a for loop, the default action is to iterate over the dict keys. So the following are equivalent:

# using 'key()' method
for key in my_dict.keys():
    print(my_dict[key])

# using default action:
for key in my_dict.:
    print(my_dict[key])

To complete the topic, you can iterate over the values of a dict using my_dict.values(), and you can iterate over a tuples of key / value pairs using my_dict.items().

Nathan Tallack
Nathan Tallack
22,159 Points
Nathan Tallack
Nathan Tallack
22,159 Points

Oh wow. I did not know that the default action was to use the keys method. That is awesome.

I really should start reading the header files for some of these types so that I can learn cool things like that. But there is just so much content here on TT that I hardly find time to do any research myself. :P