我使用Python 3.4.2制作了这个python程序。 在开始时我定义了一个变量'best', 后来它可以在函数(我没有忘记'全球最好')中进行更改。 每次改变它的印刷('新的最好',最好) 在程序结束时,它再次印刷最好的价值,但它不同于它上次改变的时间......这怎么可能?Python全局变量本身改变....为什么?
大部分的代码是不是这个重要的(我猜),但有什么用最好做的线都标有##########
from time import clock
size = [int(i) for i in input().split()]
step = [int(i) for i in input().split()]
clock()
best = [[0 for i in range(size[1])] for i in range(size[0])] ##########
best[0][0] = 1 ##########
lenbest=1 ##########
if step[0] == step[1]:
xstep = step[0]
moves = [[xstep,xstep],[-xstep,xstep],
[xstep,-xstep],[-xstep,-xstep]]
try:
best[xstep][xstep] ##########
posToGo = [moves[0]]
except: None
else:
moves = [[step[0],step[1]],[step[1],step[0]],
[-step[0],step[1]],[-step[1],step[0]],
[step[0],-step[1]],[step[1],-step[0]],
[-step[0],-step[1]],[-step[1],-step[0]]]
try:
best[step[0]][step[1]] ##########
posToGo = [moves[0]]
except: None
try:
best[step[1]][step[0]] ##########
posToGo.append(moves[1])
except: None
def attempt(board,posToGo,step):
currentMoves = []
for pos in posToGo:
currentMoves.append([pos])
for move in moves:
try:
x = pos[0]+move[0]
y = pos[1]+move[1]
if x>-1 and y>-1 and not board[x][y]:
currentMoves[-1].append([x,y])
except:None
currentMoves.sort(key=len)
for move in currentMoves:
nboard = board
nboard[move[0][0]][move[0][1]] = step
attempt(nboard,move[1:],step+1) ########## Note that i'm calling a function within itself
if step>lenbest: ##########
print("new best with pathlength",step-1,"after",clock(),"secconds")
global lenbest ##########
lenbest = step ##########
global best ##########
best = board ##########
print("in the def",best) ########## This one differs from...
attempt(best,posToGo,2) ##########
print("at the end",best) ########## ... this one. ??!!
随着输入(举例):
8 8
1 2
我得到这样的输出:
new best with pathlength 64 after 0.0017115690152521709 secconds
in the def [[1, 16, 63, 34, 3, 18, 21, 36], [64, 33, 2, 17, 52, 35, 4, 19], [15, 62, 49, 58, 45, 20, 37, 22], [32, 59, 44, 53, 48, 51, 42, 5], [61, 14, 57, 50, 43, 46, 23, 38], [28, 31, 60, 47, 54, 41, 6, 9], [13, 56, 29, 26, 11, 8, 39, 24], [30, 27, 12, 55, 40, 25, 10, 7]]
at the end [[1, 4, 3, 4, 3, 4, 5, 20], [4, 5, 2, 3, 4, 5, 4, 5], [3, 2, 13, 4, 3, 4, 7, 6], [14, 3, 4, 3, 10, 5, 4, 5], [3, 4, 3, 4, 5, 4, 5, 6], [4, 13, 4, 7, 4, 11, 6, 7], [13, 10, 13, 8, 7, 8, 7, 8], [14, 13, 8, 9, 10, 7, 8, 7]]
所以这是不同的,而这只是更换一次(算上线说“新的最好的....”):“(
'nboard = board'不会创建副本;它仅仅为同一个对象创造了另一个参考。 – 2014-11-24 20:05:01
尝试使用返回值而不是全局值。 – wenzul 2014-11-24 20:06:24