On Feb 18, 4:16 pm, "Neil" <rubik_wiz...@no.spamhotmail.com> wrote:
> Hello
>
> Sorry if this is not an appropriate newsgroup for this problem. I am very
> new to Python but not new to programming.
>
> I am hoping to use Python to teach a class and have been looking at the
> online book 'Snake Wrangling for Kids'.
>
> I have followed the example
>
> >>>import turtle
> >>>t=turtle.pen()
You defined "t" to be a pen object, not a turtle object.
>
> which works fine and displays a turtle in a window.
>
> However whenever I try to use something like
>
> >>>t.forward(50) (taken from the book)
Pens don't move, turtles move (and the pen the turtle is
carrying draws a line, if down).
>
> i get the error...
>
> Traceback (most recent call last):
> File "<pyshell#3>", line 1, in <module>
> t.forward(50)
> AttributeError: 'dict' object has no attribute 'forward'
>
> I get the same error with t.left(10) etc. etc.
Pens can't turn left, turtles turn left.
>
> I have tried this with V2.6 and V3
>
> Any ideas would be much appreciated.
>
> Thanks
> Neil
Here's an example. It draws a Minimal Spanning Tree.
If you don't need an MST, take note of how I use the turtle.
import turtle
import random
import copy
def build_sv(start,stop,limit,C):
"""Sequence Vector Generator
build_sv(start,stop,limit,C)
start: start of Collatz sequence (must be odd)
stop: sequence termination
limit: max length of [sv] if stop not found
limit is sum(sv), not len(sv)
C: C of 3n+C
returns [] if invalid
returns SequenceVector [sv]
"""
ONE = 1
TWO = 2
TWE = 3
sv = []
if (start % 2)==0: return sv
done = 0
count = 0
while done==0:
#
# oops, power division may skip past stopping point
# without seeing it
#
start = TWE*start + C
f = 0
t = start
while t%2==0:
f += 1
t /= 2
g = 0 # stopping point may occur before f is
reached
while (not done) and g<f:
start = start >> 1
if start==stop: done = 1
count += 1
g += 1
if count==limit: done = 1
sv.append(g)
return sv
def Type12MH(k,i):
"""Find ith, kth Generation Type [1,2] Mersenne Hailstone using the
closed form equation
Type12MH(k,i)
k: generation
i: member of generation
returns Hailstone (a)
"""
ONE = 1
TWO = 2
SIX = 6
NIN = 9
if (k<1) or (i<1): return 0
a = (i-ONE)*NIN**(k-ONE) + (NIN**(k-ONE) - ONE)/TWO + ONE
return TWO**(SIX*a - ONE) - ONE
turtle.clear()
turtle.up()
the_window = (turtle.window_width(),turtle.window_height())
print the_window,
turtle.goto(0,0)
tooter = turtle.position()
buffer_L = -((the_window[0]-200)/2)
buffer_R = (the_window[0]-200)/2
buffer_T = (the_window[1]-200)/2
buffer_B = -((the_window[1]-200)/2)
print buffer_L,buffer_R,buffer_T,buffer_B
turtle.tracer(False)
turtle.down()
turtle.speed('fastest')
t = 0
turtle.setheading(t)
for j in range(1):
p = Type12MH(4,2) # Type12 Mersenne Hailstone (very big)
sv = build_sv(p,1,10000000,1) # limit to 10 million numbers in
vector
# Minimal Spanning Tree
stars = []
turtle.up()
for d in sv: # random turtle crawl based on
sv
if d>1: # skip small sv values for
movement
for r in xrange(1):
turtle.setheading(t+r*90)
turtle.forward(d*4) # scale of grid
tooter = turtle.position()
if d>8: # create a star at really large sv
values
turtle.down()
turtle.width(3)
turtle.color('black')
turtle.forward(1) # draw a blob
turtle.backward(1)
stars.append((int(tooter[0]),int(tooter[1])))
turtle.up()
turtle.width(1)
turtle.color('red') # color of MST spans
whither_tooter = [] # build list of legal next turns
if tooter[0]>buffer_L: # test for being too close to
screen edge
whither_tooter.append(180)
if tooter[0]<buffer_R:
whither_tooter.append(0)
if tooter[1]<buffer_T:
whither_tooter.append(90)
if tooter[1]>buffer_B:
whither_tooter.append(270)
t = random.choice(whither_tooter) # choose random direction from
list of legal moves
print 'stars:',len(stars)
star_dist = [] # create list of spans between
stars
for i,src in enumerate(stars):
for j,dst in enumerate(stars):
dist = turtle.sqrt((src[0]-dst[0])**2 + (src[1]-dst[1])**2)
if dist == 0:
star_dist.append([9999,i,j])
else:
star_dist.append([dist,i,j])
star_dist.sort()
MST = [] # spans of MST
MST2 = [] # only those spans that can
connect to existing MST
points_used = {} # list of stars that are
currently on MST
s = copy.deepcopy(star_dist[0]) # going to modify list element,
so deep copy needed
MST.append(s) # fist span always smallest
absolute distance
points_used[s[1]] = 1
points_used[s[2]] = 1
star_dist[0][0] = 9999 # overwrite distance so this
span can't be used again
found = False # also, overwrite complement
span
si = 0
while not found:
ss = star_dist[si]
if s[1]==ss[2] and s[2]==ss[1]: # the complement
star_dist[si][0] = 9999
found = True
else:
si += 1
while len(MST)<(len(stars)-1): # an MST of n points always
has n-1 spans
for i,sd in enumerate(star_dist): # copy points matching s to MST2
# only spans that could connect to existing
# tree points can be added at this stage
# (only have to check for last added to MST)
if (sd[0]!=9999) and \
((sd[1]==s[1]) or \
(sd[1]==s[2]) or \
(sd[2]==s[1]) or \
(sd[2]==s[2])):
MST2.append(copy.deepcopy(sd))
star_dist[i][0] = 9999 # once copied to MST2, overwrite
original distance
MST2.sort()
close = 0
#
# can't use a span if BOTH points already on MST, otherwise we get
loops
# and some stars remain disjoint
#
while ((MST2[close][1] in points_used) and (MST2[close][2] in
points_used)):
close += 1
s = copy.deepcopy(MST2[close])
MST.append(s)
if s[1] in points_used: # only keys used to create tree,
values
points_used[s[1]] += 1 # will eventully be number of
points
else: # connected to this point
points_used[s[1]] = 1
if s[2] in points_used:
points_used[s[2]] += 1
else:
points_used[s[2]] = 1
MST2[close][0] = 9999 # overwrite this point and its
complement
found = False
si = 0
while not found:
ss = MST2[si]
if s[1]==ss[2] and s[2]==ss[1]: # the duplicate
MST2[si][0] = 9999
found = True
else:
si += 1
if si == len(MST2): found = True
for span in MST: # from an MST span
srcx = stars[span[1]][0] # get coords of two endpoints
srcy = stars[span[1]][1]
dstx = stars[span[2]][0]
dsty = stars[span[2]][1]
turtle.up() # and draw a line between them
turtle.goto(srcx,srcy)
turtle.down()
turtle.goto(dstx,dsty)
--
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