我是Python的新手,很惊讶地发现我的代码的这一部分:
print len(allCommunities[5].boundary)
allCommunities[5].surface = triangularize(allCommunities[5].boundary)
print len(allCommunities[5].boundary)
输出:
1310
2
下面是我在Processing(像Java这样的语言)中编写并移植到Python中的函数。它完成它应该做的(三角形多边形),但我的目的是通过inBoundary
来使用函数但不删除allCommunities[5].boundary
中的元素。
我应该如何防止在功能中修改allCommunities[5].boundary
?在旁注中,如果我在函数中做一些愚蠢的事情,我会很感激指针,但仍然习惯于Python。
def triangularize(inBoundary):
outSurface = []
index = 0;
while len(inBoundary) > 2:
pIndex = (index+len(inBoundary)-1)%len(inBoundary);
nIndex = (index+1)%len(inBoundary);
bp = inBoundary[pIndex]
bi = inBoundary[index]
bn = inBoundary[nIndex]
# This assumes the polygon is in clockwise order
theta = math.atan2(bi.y-bn.y, bi.x-bn.x)-math.atan2(bi.y-bp.y, bi.x-bp.x);
if theta < 0.0: theta += math.pi*2.0;
# If bp, bi, and bn describe an "ear" of the polygon
if theta < math.pi:
inside = False;
# Make sure other vertices are not inside the "ear"
for i in range(len(inBoundary)):
if i == pIndex or i == index or i == nIndex: continue;
# Black magic point in triangle expressions
# http://answers.yahoo.com/question/index?qid=20111103091813AA1jksL
pi = inBoundary[i]
ep = (bi.x-bp.x)*(pi.y-bp.y)-(bi.y-bp.y)*(pi.x-bp.x)
ei = (bn.x-bi.x)*(pi.y-bi.y)-(bn.y-bi.y)*(pi.x-bi.x)
en = (bp.x-bn.x)*(pi.y-bn.y)-(bp.y-bn.y)*(pi.x-bn.x)
# This only tests if the point is inside the triangle (no edge / vertex test)
if (ep < 0 and ei < 0 and en < 0) or (ep > 0 and ei > 0 and en > 0):
inside = True;
break
# No vertices in the "ear", add a triangle and remove bi
if not inside:
outSurface.append(Triangle(bp, bi, bn))
inBoundary.pop(index)
index = (index+1)%len(inBoundary)
return outSurface
print len(allCommunities[5].boundary)
allCommunities[5].surface = triangularize(allCommunities[5].boundary)
print len(allCommunities[5].boundary)
答案 0 :(得分:4)
Python中的列表是可变的,以及诸如
之类的操作inBoundary.pop
修改它们。简单的解决方案是复制函数内的列表:
def triangularize(inBoundary):
inBoundary = list(inBoundary)
# proceed as before
答案 1 :(得分:3)
最简单的方法是制作参数的副本:
def triangularize(origBoundary):
inBoundary = origBoundary[:]
然后你的其余代码可以保持不变。