难以通过python与qhull进行管道连接

Question

我在python中通过QHull管道传输命令时遇到问题。我目前正尝试这样做：

input_command = "rbox c " + str(qpoints) + " | qconvex FQ FV n"
command = subprocess.Popen(input_command.split(" "), stdout=subprocess.PIPE)
print command.communicate()[0]

在这里，qpoints被格式化为input_command最终为：

rbox c P0,0,0 P0,0,2 P0,2,0 P0,2,2 P2,0,0 P2,0,2 P2,2,0 P2,2,2 | qconvex FQ FV n

不幸的是，这只是打印出了q凸面的用法：

qconvex- compute the convex hull.  Qhull 2012.1 2012/02/18
    input (stdin): dimension, number of points, point coordinates
    comments start with a non-numeric character
options (qconvex.htm):
    Qt   - triangulated output
    QJ   - joggled input instead of merged facets
    Tv   - verify result: structure, convexity, and point inclusion
    .    - concise list of all options
    -    - one-line description of all options
output options (subset):
    s    - summary of results (default)
    i    - vertices incident to each facet
    n    - normals with offsets
    p    - vertex coordinates (includes coplanar points if 'Qc')
    Fx   - extreme points (convex hull vertices)
    FA   - report total area and volume
    FS   - compute total area and volume
    o    - OFF format (dim, n, points, facets)
    G    - Geomview output (2-d, 3-d, and 4-d)
    m    - Mathematica output (2-d and 3-d)
    QVn  - print facets that include point n, -n if not
    TO file- output results to file, may be enclosed in single quotes
examples:
    rbox c D2 | qconvex s n                    rbox c D2 | qconvex i
    rbox c D2 | qconvex o                      rbox 1000 s | qconvex s Tv FA
    rbox c d D2 | qconvex s Qc Fx              rbox y 1000 W0 | qconvex s n
    rbox y 1000 W0 | qconvex s QJ              rbox d G1 D12 | qconvex QR0 FA Pp
    rbox c D7 | qconvex FA TF1000

我在网上读到了一些在python调用中包含管道时必须采取的额外步骤的例子。但我找不到它们的任何例子，也几乎没有解释发生了什么。有人能在这里向我解释一个有效的代码片段吗？为什么有效？

我还试着从文件中读取一个函数的结果。例如，我尝试从文件中读取rbox的结果

python代码：

input_command =  "qconvex FQ FV n < rbox.txt"
    command = subprocess.Popen(input_command.split(" "), shell=True)
    result = command.communicate()
    return result

数据：

3 rbox c P1,1,1 P1,1,3 P1,3,1 P1,3,3 P3,1,1 P3,1,3 P3,3,1 P3,3,3
16
     1      1      1 
     1      1      3 
     1      3      1 
     1      3      3 
     3      1      1 
     3      1      3 
     3      3      1 
     3      3      3 
  -0.5   -0.5   -0.5 
  -0.5   -0.5    0.5 
  -0.5    0.5   -0.5 
  -0.5    0.5    0.5 
   0.5   -0.5   -0.5 
   0.5   -0.5    0.5 
   0.5    0.5   -0.5 
   0.5    0.5    0.5 

不过，这仍然只是打印出QConverx的描述。奇怪的是，这在命令行中运行得非常好，只是没有通过python。即使我不能让管道去上班，我也绝对需要从文件中读取信息来上班。有人知道调用这个函数的诀窍吗？

Answer 1

• 如果使用|等shell功能或使用纯Python重写命令，请使用shell=True，请参见替换shell管道
• 如果使用shell=True，则将命令作为文档中指定的字符串传递

from subprocess import check_output as qx
output = qx("rbox c {qpoints} | qconvex FQ FV n".format(qpoints=qpoints),
            shell=True)
print output