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Variables, Lists, and Dictionaries (2/3)

Multi-part variables

In addition to storing single pieces of data, you can also use variables to store many pieces of data, and then access them in a structured way. There are two basic types of multi-part variables:

  • Lists (sometimes called arrays)
  • Dictionaries (sometimes called key-value pairs)

Working with Lists

A List can be created by using square brackets, and separating individual elements by commas like so:

numbers = [1, 2, 3, 4, 5]
fruits = ['apples', 'oranges', 'bananas']

To retrieve an object from such a List, you once again use square brackets, but this time appended to the end of the variable name. Inside the brackets you place the index or position of the item you want in the List. For example:

numbers = [1, 2, 3, 4, 5]
print(numbers[0])
fruits = ['apples', 'oranges', 'bananas']
print(fruits[1])

Notice that like in all languages (including Grasshopper), counting begins with '0', so if you want the first item in a list you use [0], the second item [1], and so on. Unlike many other languages, Python will allow you to mix different types of data within a single List, so something like this is perfectly legal:

fruitsAndNumbers = ['apples', 2, 'bananas']
print(type(fruitsAndNumbers))
print(type(fruitsAndNumbers[0]))
print(type(fruitsAndNumbers[1]))

You can also use a : operator within the square brackets to obtain a range of values from a List, which will create a new list that you can assign to a new variable:

numbers = [1, 2, 3, 4, 5]
newNumbers = numbers[0:3] # [index of first item:index after last item]
print(newNumbers)

You can even index backwards using negative indices. Here is a typical application that will print out the last item in the List:

numbers = [1, 2, 3, 4, 5]
print(numbers[-1])

Lists implement various methods to help you work the data stored within. The most common is .append(), which adds a value to the end of a List:

numbers = [1, 2, 3, 4, 5]
numbers.append(6)
print(numbers)

You can even start with an empty List, and fill it gradually with appends:

numbers = []
numbers.append(1)
numbers.append(2)
print(numbers)

For other common List methods you can refer to the Python documentation.

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