子进程，Popen Python

Question

我想运行一个程序，比如MATLAB或其他来自Python的FEA软件，等待它运行并存储结果，然后再用Python进行处理。 我无法找到一个关于如何这样做的真正基本的例子。 一个简单的代码或任何有用的链接将受到高度赞赏。 Subprocess模块​​的帮助看起来有点复杂。

Answer 1

我只是花了一些时间试图从令人沮丧的模糊文档和示例中解决这个问题，最后弄明白了。 这是一个非常简单的演示示例：

如何从Python运行MATLAB脚本 （使用subprocess.Popen，无需安装matlab引擎）

第1步：创建要运行的MATLAB脚本。 在这个演示中，我有两个脚本，保存在文件夹C：/ Users / User / Documents / MATLABsubprocess中：

triangle_area.m

b = 5;
h = 3;
a = 0.5*(b.* h);  
save('a.txt','a', '-ASCII')

triangle_area_fun.m

function [a] = triangle_area(b,h)
a = 0.5*(b.* h);   %area
save('a.txt','a', '-ASCII')
end

步骤2：创建这两个.m文件后，以下Python脚本使用subprocess.Popen（）运行它们：

#Imports:
import subprocess as sp
import pandas as pd

#Set paths and options:
#note: paths need to have forward slashes not backslashes (why?!)
program  = 'C:/Program Files/MATLAB/R2017b/bin/matlab.exe'  #path to MATLAB exe
folder   = 'C:/Users/User/Documents/MATLABsubprocess'       #path to MATLAB folder with scripts to run
script   = 'triangle_area'                                  #name of script to run
options  = '-nosplash -nodesktop -wait'                     #optional: set run options  (nosplash? nodesktop means MATLAB won't open a new desktop window, wait means Python will wait until MATLAB is done beore continuing (needs to be paired with p.wait() after sp.Popen))
has_args = True                                             #set whether the MATLAB script needs arguments (i.e. is it a function?)

#Optional: define arguments to feed to function
if has_args ==True:
    script   = 'triangle_area_fun'                          #select script version with arguments
    b = 5 
    h = 3
    args = '({},{})'.format(b,h)                            #put all args into one string

#Set function string:
#Structure:  """path_to_exe optional_arguments -r "cd(fullfile('path_to_folder')), script_name, exit" """
#Example:    """C:/Program Files/MATLAB/R2017b/bin/matlab.exe -r "cd(fullfile('C:/Users/User/Documents/MATLABsubprocess')), triangle_area, exit" """
#basically, needs to know where the program to use lives, then takes some optional settings, -r runs the program, cd changes to the directory with the script, then needs the name of the script (possibly with arguments), then exits
fun =  """{} {} -r "cd(fullfile('{}')), {}, exit" """.format(program, options, folder, script)  #create function string that tells subprocess what to do
if has_args==True:
    fun = """{} {} -r "cd(fullfile('{}')), {}{}, exit" """.format(program, options, folder, script, args)
print('command:', fun)

#Run MATLAB:
print('running MATLAB script...')
p = sp.Popen(fun)                     #open the subprocess & run the MATLAB script 
p.wait()                              #wait until MATLAB is done before proceeding (this needs to be paired with -wait in options)
print('done')                         #if the run is successful, an output file named a.txt should appear in the folder with the MATLAB scripts

#Import MATLAB output files back into Python:
a = pd.read_csv('a.txt', header=None)             #read text file using pandas
print(a)