从字典值中检索函数

Question

all! As a personal project of mine, I'm attempting to convert a dice roll animation in tkinkter from using only if statements to dictionary values instead. I'm essentially doing this:

def draw_dice(*args):
    w,h = 23, 23
    x,y,r = 2,2,5
    c = tk.Canvas(root,width=w,height=h,bg='white')

    dots = {
        'dot0':None,
        'dot1':c.create_oval(x, y, x + r, y + r, fill='black'),
        'dot2':c.create_oval(x + 16, y, (x + 16) + r, y + r, fill='black'),
        'dot3':c.create_oval(x, y + 8, x + r, (y + 8) + r, fill='black'),
        'dot4':c.create_oval(x + 8, (y + 8), (x + 8) + r, (y + 8) + r, fill='black'),
        'dot5':c.create_oval(x + 16, (y + 8), (x + 16) + r, (y + 8) + r, fill='black'),
        'dot6':c.create_oval(x, y + 16, x + r, (y + 16) + r, fill='black'),
        'dot9':c.create_oval(x + 16, y + 18, (x + 16) + r, (y + 16) + r, fill='black')
    }

    for arg in args:
        dots.get(arg)

    return c

The code runs, but the output is not as expected. For the *args passed into the function, select values can be:

'dot0', 'dot1'..., 'dot9' or just simply 'dot1'.

Within another function of mine, I append the returned c (canvas) to a list that will shuffle through the various created dice faces to animate a rolling dice.

But, that's not the problem. The problem is coming from this function. After running the debugger, I've discovered that the values for each key are like this:

'dot0':None, 'dot1':1, 'dot2': 2, etc.

Something odd is going on, but I'm suspicious that I may be using this data structure wrong. Any help would be greatly appreciated!

Answer 1

As it is, the dictionary does not have functions, it has the output of functions that have already been invoked.

At the time the interpreter sees the line

 'dot1':c.create_oval(x, y, x + r, y + r, fill='black')

it actually runs the create_oval method, which returns an auto-incremented integer id for the oval. So, after that 'dot1': 1

if you want it to be a function you could do something like

 'dot1': lambda x, y, r: c.create_oval(x, y, x + r, y + r, fill='black')

The same of all dotX keys. Then, you can call it in your loop by

 for arg in args:
     dots.get(arg)(x, y, r)

Answer 2

You have defined eg dot1 as:

'dot1': c.create_oval(x, y, x + r, y + r, fill='black')

This is evaluated when your dictionary is created. The c.create_oval() function does not return anything, so it returns None . This value is stored in the dictionary.

Presumably you want to defer execution of these calls until you actually call draw_dice() . To do this, you need to make the value of your dictionary items functions. The easiest way of doing this is to use lambda to define a one-line anonymous function:

'dot1': lambda: c.create_oval(x, y, x + r, y + r, fill='black')

And when you iterate through your arguments, call the function:

for arg in args:
     dots[arg]()