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- [Instructor] Before
we get into the syntax

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of building dictionaries in Python,

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let's talk a little bit about

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the contents of a dictionary.

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Again, a dictionary maps keys to values.

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The keys have a couple of requirements.

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They must be unique,

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and the value that is used as the key

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must be of an immutable data type.

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As you can see in the table

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that we're showing you here,

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we have some key types that
are strings and integers.

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The value types can be whatever you want.

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They can be mutable or immutable.

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These are just some examples

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of potential key value pairs.

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We could map, for
example, a country's name

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over to its Internet country code,

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or we could take a decimal integer value

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and map it over to its Roman
numeral representation.

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Or for a state in the United States,

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we might have a list

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of corresponding agricultural products.

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You can see a number of other ones here

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in this table as well.

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Again, a couple of key things.

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The keys must be unique.

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The keys must be immutable

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so that we can be guaranteed

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to find the corresponding
value again in the future.

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The values are not required to be unique

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in this right-hand column here.

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You can have whatever values you want

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for each individual key.

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The value types can be of either mutable

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or immutable types in Python.