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At the moment, our program uses the country 
name as the key into the countries dictionary. 

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We also want to allow the user to 
enter a two-letter country code. 

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We have all the data we need, but we 
have to decide how we're going to use it. 

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One approach would be to create 
a separate dictionary, 

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to look up the country names for the codes.
So we might do something like this: 

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We'd have to define an empty dictionary called 
code_lookup, at the start of the program. 

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Then we could check the length of 
the user's input, and look up the 

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country name if they only enter two letters.
That's a viable solution, and would work fine. 

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If you want to try to do it that 
way, it would be a good exercise. 

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I'm going to use a different approach, because 
it might not be obvious that you can do this. 

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There's no reason why values, in a dictionary, 
can't have more than one key. We can add another 

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key to the countries dictionary, and give 
it the same value as the country name. 

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I'll comment out that line I 
just typed, and add a new key: 

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The countries dictionary will now contain two 
references to the dictionaries for each country. 

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One with the country name as the key, and 
another with the country code as the key. 

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Note that the individual country 
dictionaries are not duplicated. 

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As we saw in the last section, countries is 
storing references to the individual dictionaries. 

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They're not being copied by the code on line 22.
The dictionary will use more memory, of course. 

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But not significantly more than 
creating another dictionary. 

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This approach has the advantage that we don't 
have to change the remainder of our code. 

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You might want to change the prompt, on 
line 27, but that's just a cosmetic change. 

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This code will work with either 
a country name, or a code. 

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I'll run the program, to confirm that. Quit first, 
if you've still got the program running from the 

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previous video, then run the program again.
I'll enter au, which is the ISO country code 

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for Australia, and the program 
prints the correct capital city. 

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Entering Australia also works, 
and we get "Canberra" again. 

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Alright, that's been a useful example 
of reading data from a text file, 

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and getting it into a format 
that we can use with our code. 

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Before we look at writing data to a text 
file, practise with some changes to this code. 

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It would be more informative if you printed 
a suitable message, for countries like 

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Antarctica that don't have a capital city.
To test that change, you'll want to identify 

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the countries that don't have a value for their 
capital field. Write some code to iterate over 

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the dictionary, and print the country 
name of any country without a capital. 

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Expand that code, to print the country 
and field name for all blank values. 

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You could also print a suitable message 

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if the user enters something 
invalid for the country name. 

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Those are some ideas for you to use this 
example, to practise your programming. 

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Experiment, have fun, and I'll 
see you in the next video.