E.Elle E.Elle - 9 months ago 39
Python Question

Turtle graphics animation (shelf)

I want to define a function

insert_animate(blockposition, shelf, high)
such that it removes the block at
blockposition
from
shelf
and insert this block into a high position at
high
, where
high
is an integer. The function should find this position between zero and the high position, non-inclusive of high. If no such position is found, the block is inserted at the high position.

I've managed to come up with this function:

def insert_animate(blockposition, shelf, high):
if blockposition==0:
return shelf
else:
a=s.pop(blockposition)
for i in range(high):
if a.size<=s[i].size:
s.insert(i,a)
break
else:
s.insert(high,a)
return shelf


However, this only works on some cases, not all. I am not sure where I went wrong.

s = shelf.init_shelf((2, 6, 1, 4, 8, 3, 9))
print(insert_animate(0, s, 0)) # returns [Block size: 2, Block size: 6, Block size: 1, Block size: 4, Block size: 8, Block size: 3, Block size: 9]
print(insert_animate(3, s, 3))
# returns [Block size: 1, Block size: 2, Block size: 4, Block size: 6, Block size: 4, Block size: 4, Block size: 8, Block size: 3, Block size: 9]


But it should be (for second print):

[Block size: 1, Block size: 2, Block size: 4, Block size: 6, Block size: 4, Block size: 4, Block size: 8, Block size: 3, Block size: 9]

print(insert_animate(6, s, 6))
# returns [Block size: 1, Block size: 2, Block size: 4, Block size: 6, Block size: 4, Block size: 4, Block size: 8, Block size: 8, Block size: 8, Block size: 8, Block size: 8, Block size: 8, Block size: 3, Block size: 9]


But it should be:

[Block size: 1, Block size: 2, Block size: 4, Block size: 6, Block size: 8, Block size: 3, Block size: 9]


Why does my code work for some cases but not for others? Does the issue lie on my for-loop? If anyone could help I would really appreciate it! Thank you!

This is the file that I'm working on:

from turtle import *

class Block(Turtle):
def __init__(self, size):
self.size = size
Turtle.__init__(self, shape="square", visible=False)
self.pu()
self.shapesize(size * 1.5, 1.5, 2) # square-->rectangle
self.fillcolor("black")
self.st()
def glow(self):
self.fillcolor("red")
def unglow(self):
self.fillcolor("black")
def __repr__(self):
return "Block size: {0}".format(self.size)

class Shelf(list):
def __init__(self, y):
"create an shelf. y is y-position of first block"
self.y = y
self.x = -150
def push(self, d):
width, _, _ = d.shapesize()
yoffset = width/2 * 20 # to align the blocks by it's bottom edge
d.sety(self.y + yoffset)
d.setx(self.x+34*len(self))
self.append(d)
def _close_gap_from_i(self, i):
for b in self[i:]:
xpos, _ = b.pos()
b.setx(xpos - 34)
def _open_gap_from_i(self, i):
for b in self[i:]:
xpos, _ = b.pos()
b.setx(xpos + 34)
def pop(self, key):
b = list.pop(self, key)
b.glow()
b.sety(200)
self._close_gap_from_i(key)
return b
def insert(self, key, b):
self._open_gap_from_i(key)
list.insert(self, key, b)
b.setx(self.x+34*key)
width, _, _ = b.shapesize()
yoffset = width/2 * 20 # to align the blocks by it's bottom edge
b.sety(self.y + yoffset)
b.unglow()

def show_text(text):
goto(0,-250)
write(text, align="center", font=("Courier", 16, "bold"))

def start_sort():
onkey(None,"space")
clear()
show_text("sort_me")
sort_func(s)

def init_shelf(vals=(4, 8, 2, 9, 3, 1, 10, 7, 5, 6)):
s = Shelf(-200)
for i in vals:
s.push(Block(i))
return s

def clear_window():
getscreen().clearscreen()

def main(func):
global sort_func
sort_func = func
getscreen().clearscreen()
ht(); penup()
init_shelf()
show_text("press spacebar to start sorting")
onkey(start_sort, "space")
onkey(bye, "Escape")
listen()
mainloop()

Answer Source

It's hard to follow your examples of starting order and final order after calling insert_animate() but here's my guess at what's going wrong:

I believe you've got your else clause indented incorrectly (too deep) such that it has become part of the if statement when it really should be part of the for statement:

def insert_animate(blockposition, shelf, high):

    if blockposition == 0:
        return shelf

    a = s.pop(blockposition)

    for i in range(high):
        if a.size <= s[i].size:
            s.insert(i, a)
            break
    else:  # no break
        s.insert(high, a)

    return shelf

As originally written, the else clause could be executed multiple times but you only want it executed once, when the for loop exits via a means other than break. An else clause tied to a loop in this manner can be thought of as meaning "no break", i.e. execute this code if the loop has a break statement but it wasn't taken.