Artists sometimes collect a list of colors in a "palette".

Defining a Color Palette

Here is a palette of colors we name artsy_rainbow. Each color is created from its red, green, and blue components using the rgb_color function.

Visualizing a Color Palette

Let's program a function that takes a palette (a list of colors) and returns a graphic visualizing that palette. The graphic consists of one circle per color, and all circles are placed beside each other. The first color's circle is placed on the left.

A call to horizontal_palette(artsy_rainbow) should look like this:

Colored Sectors

Now let's create a circle composed of sectors, one sector for each color.

We use the enumerate function provided by Python. We call the function with a list of colors, and it produces a list of index-color tuples.

The for-loop thus iterates over the list of tuples, and each time gives us one such tuple. We destructure that tuple into the variables index and color.

Thus, in the loop body we have available the current index (0 to 23 in our case), the current color, the angle of a single sector (360 / 24 = 15), and result, the variable accumulating the resulting graphic.

Outlined Colored Sectors

We would like to have a black outline around each sector, like this:

The outline consists of two parts: a rounded arc, and straight lines. To get the rounded arc, we place a slightly smaller colored sector on top of a black sector. To get the straight lines, we place a black rectangle on top of the sector.

Color Swirl

Finally, let's compose multiple outlined color circles into a color swirl.

To do this, we rotate each color circle a bit more (or less) than the prior circle. Let's name this "between-circle rotation" the twist: A twist of 0.0 means the absence of twist, a twist of -1.0 means each circle is rotated clock-wise by one segment with respect to the next smaller circle, and a twist of 1.0 means each circle is rotated counter-clock-wise by one segment with respect to the next smaller circle

Save In Your Toolbox

We hope you like these color swirls! Save your color_swirl function in your toolbox. You might want to use it somewhere else in the future!

What You Learned

You learned how to:

• determine the length of a list with len(l)
• iterate over the elements of a list with for e in l
• iterate over the element-index tuples of a list with for (e, i) in enumerate(l)
• iterate over the indices of a list with for i in range(len(l))
• iterate over numbers from 0 to n with for i in range(n)

Note that all four ways to iterate are based on the exact same for-construct. The difference is that in each of the four cases we provide a different list to iterate over:

1. a list of colors with l
2. a list of tuples with enumerate(l)
3. a list of indices with range(len(l))
4. a list of numbers from 0 to n with range(n)

The second-to-last case is just a variant of the last case, because len(l) evaluates to a number, and thus we call range with a number as an argument in both cases.