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- [Instructor] So now that we've seen

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how to write a CSV file as arrays, in this example,

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we're going to see how to write a CSV file

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using dictionaries for the data source instead of arrays.

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So in this example code, let's open up write_csv_dict.py.

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And I've already got a list of dictionary objects

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that represent a subset of the data

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in the inventory file that we've been using.

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So you can see that this is a little bit

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of a different format than we had in the previous example.

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The first thing I need to do is define the column names

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that will be the header row for the output CSV file.

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This is required by the DictWriter object we're going

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to be using in the CSV module, so it knows how

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to map each dictionary key to a particular column.

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So you can see in the sample data

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that the items in each row consists of a key and a value.

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The fieldnames parameter will be used to match

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each of the keys to one of the output columns.

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And this is required by the DictWriter.

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This is not optional like it was in the reading example.

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So what I'm going to do is create a fieldnames variable.

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And that's going to be a list of the keys in my data.

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So I'm going to have Item Name, Category, Quantity.

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And then we'll have the Wholesale Price

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and the Consumer Price.

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And these need to match each of the keys

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that you have in your dictionary.

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So make sure that they're spelled correctly,

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otherwise it's going to cause a problem.

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All right, so now let's build our function

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to write the CSV file.

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So I'm going to call that write_dict_to_csv.

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And once again, that will take the data and the filename.

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So similar to the previous example,

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we will open our file for writing.

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So we'll open the filename in write mode with line endings.

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Oops.

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And we'll open that as CSV file.

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Only this time, we're going to use a DictWriter

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to write the data.

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And this is where we supply the field names

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that we've created.

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So I'm going to create a writer variable

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and that's going to be an instance of the DictWriter class.

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And I'm going to pass in the CSV file that we created,

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and I'm going to specify that fieldnames is equal

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to the fieldnames variable that we've created.

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And then we'll just write the data as usual.

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So we'll call writer,

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and I'm going to call writeheader first.

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That will output all the field names as the header row.

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And then I'll call writer.writerows,

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and we'll pass in the array of dictionaries.

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And once again, I just need to call the function

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for all this to work.

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So let's go ahead and call our function

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and we'll pass in the data.

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And once again we'll call it output.csv.

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All right, so let's save, that should about do it.

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Let's run our code.

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So we'll run this in the terminal,

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and when I run it, we can see output.csv was created

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and everything looks good.

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Take a look at that.

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Sure enough, CSV data looks right.

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We've got our header row, Item Name, Category, Quantity,

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Wholesale, Consumer Price, along with all of the values

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that we wrote out in our dictionaries.