Project2:解读percolation_provided
Updated 1st:2011.8.7 
这里咱们开始解读项目2中提供的percolation_provided.py，一共提供了4个函数，分别为：
printgrid(grid): prints the grid represented by the nested list, one row per line (this module may be helpful in testing and debugging your code)
printgrid(grid)：输出用嵌套列表表示的网络，每排代表一行（这一模型可能对测试和调试你的代码有帮助）
readgrid(filename): opens the file filename and returns the contents as a list of list (also helpful in testing and debugging your code)
readgrid(filename)：按文件名打开文件，并返回内容的列表清单（对测试和调试代码有帮助）
grid(size,fill=0): returns a grid of dimensions size × size in which every grid location is initialized to fill. The default fill value is 0.
grid(size,fill=0)：按size × size返回网格大小，其中每个格子的位置都被初始化填充。默认填充值为0.
visualize(flow_grid, input_grid): visualizes the flow through a grid using VPython
visualize(flow_grid, input_grid)：使用Vpython可视化流体经过网格
1.第一个是grid(size,fill=0)函数，没多大技术含量，Key Point在于为生成一个nxn的网格，需要使用一个for..range语句，以及一个长度为n的列表作为行，然后另外一个空列表添加n行这样的列表。
"""
Make a grid with 'size' rows and 'size' columns, with each space filled by
'fill'.
>>> grid(3, 1)
[[1, 1, 1], [1, 1, 1], [1, 1, 1]]
>>> grid(2, '*')
[['*', '*'], ['*', '*']]
"""
# 生成一个大小为sizeXsize的网格，默认填充为fill
grid = []
for i in range(size):
row = [fill]*size # row is a list with size copies of fill
grid.append(row)
return grid
2.第二个是printgrid(grid)函数，用来打印输出网格grid。
"""
Print out the grid represented in 'grid'.
>>> printgrid([[1,0,1],[0,1,1],[0,0,1]])
1 0 1
0 1 1
0 0 1
>>>
"""
#请注意print '%02s' % (space,),这句，其中（space,)中的逗号可省略，最后那个逗号不能省略，用于循环语句结束在同一行输出
#当然你也可以尝试一下去掉看看会出现什么结果，下一行的print用于换行，最好的学习办法就是动手试试去掉了会出现什么
for row in grid:
for space in row:
print '%02s' % (space,),
Help on method_descriptor:
split(...)
S.split([sep [,maxsplit]]) -> list of strings
Return a list of the words in the string S, using sep as the
delimiter string. If maxsplit is given, at most maxsplit
splits are done. If sep is not specified or is None, any
whitespace string is a separator.
，然后就是打开文件filename，每次读一行(for line in file)，然后弄个列表row。使用for语句把里面的元素按空格切开，依次读到x中，遍历添加到row里，如果文件读取到头了，那么row就为空列表了。
"""
Reads the grid from the file. The format is one row per line, each column
separated by whitespace.
>>> f = open('readgrid.test', 'w')
>>> print >>f, '0 1 0\\n1 0 1\\n1 1 0\\n'
>>> f.close()
>>> readgrid('readgrid.test')
[[0, 1, 0], [1, 0, 1], [1, 1, 0]]
"""
file = open(filename)
grid = []
for line in file:
row = []
for x in line.split():
x = int(x) # make x an integer, rather than string
row.append(x)
if row != []: # filter out empty lines
grid.append(row)
return grid
4.第四个是visualize(flow_grid, input_grid)函数，咱能先不谈么？对VPython的用法知之甚少啊
。随便谈一下把，这个函数用来显示在flow_grid和input_grid中的流。使用灰方块表示阻塞位置，蓝方块表示流到的到位。
"""
Visualize the flow in flow_grid on input_grid with VPython, using gray
squares for blocked spaces (input_grid[i][j] = 1) and blue squares for
spaces with flow (flow_grid[i][j] = '*').
All objects in the scene will be removed prior to drawing. The active
scene will be used.
>>> visualize([['*','*',1],['*',1,1],['*',1,1]], [[0,0,1],[0,1,1],[0,0,1]])
"""
from visual import box, display
blue = (0, 0, 1)
gray = (.5, .5, .5)
black = (0.3, 0.3, 0.3)
size = len(input_grid)
total_size = size * size
disp = display.get_selected() # gets the active display
if disp is None: # no display, so create one
display(title="Percolation", autocenter=True)
else: # display exists, empty it
disp.autocenter = True # autocenter for convenience
# We only need to delete these boxes if there is a mismatch in the
# number of boxes versus the number of grid cells. We assume that no
# other objects are on the scene.
if total_size != len(disp.objects):
for object in disp.objects:
object.visible = False # make all objects in display invisible
# redraw all of the grid, because of the size mismatch
if total_size != len(disp.objects):
for row in range(size):
for col in range(size):
# for blocked spaces, draw a gray box
if input_grid[row][col]==1:
box(pos=(col, -row, 0), color=gray)
# for spaces with flow, draw a blue box
elif flow_grid[row][col]!=-1:
box(pos=(col, -row, 0), color=blue)
else:
box(pos=(col, -row, 0), color=black)
# or just change the colors, based on the grids given
else:
for object in disp.objects:
x, y, _ = object.pos
x, y = int(x), int(y)
if flow_grid[-y][x] != -1:
object.color = blue
elif input_grid[-y][x] == 1:
object.color = gray
else:
object.color = black
def random_grid(size, p):
"""
Generates a grid with 'size' rows and 'size' columns. Each grid space is
randomly filled with a zero with probability p or a one with probability
(1-p).
>>> random_grid(3, 1)
[[0, 0, 0], [0, 0, 0], [0, 0, 0]]
>>> random_grid(3, 0)
[[1, 1, 1], [1, 1, 1], [1, 1, 1]]
"""
from random import uniform
g = grid(size, 0)
for row in range(size):
for col in range(size):
if uniform(0,1) < p: # true with probability p
g[row][col] = 0
else:
g[row][col] = 1
return g
import doctest
doctest.testmod()
