如何从python捕获matlab函数的输出 [英] How to catch output of a matlab function from python

问题描述

我运行下面的python代码来评估数组的平均值：

I'm running the python code below which evaluates mean of an array:

def matlab_func1(array):
    p = os.popen('matlab -nodesktop -nosplash  -r "mean('+str(array)+');exit"')
    while 1:
        line = p.readline()
        if not line:
            break
        print line

matlab_func1([1,2,3]) 

从下面的matlab脚本，可以看出输出返回到y。我想从python捕获这个输出。

From the matlab script below, it can be seen output return to y. I want to catch this output from python.

function y = mean(x,dim)
...
...
end

解决方案必须适用于其他matlab函数。 'mean'函数只是一个例子。

The solution must be applicable to the other matlab function. The 'mean' function is just an example.

推荐答案

使用 fprintf 将所需的文本写入 stderr 。只需在开头添加一个额外的参数 2 。

Use fprintf to write needed text into stderr. Just add an extra argument 2 in the beginning.

import subprocess
import os
def matlab_func1(array):
    p = subprocess.Popen(['/home/user/Matlab/bin/matlab', '-nodesktop', '-nosplash', '-r "m = mean(' + str(array) + ');fprintf(2, \'%d\\n\',m);exit" >/dev/null'], stdout=subprocess.PIPE, stderr=subprocess.PIPE)
    while 1:
        try:
            out, err = p.communicate()
        except ValueError:
            break
        print 'hello' + err

matlab_func1('[1,2,3]') 

需要注意的几件事：

• 将Python命令更改为 subprocess.Popen ，允许 stderr 管道。


• 在Matlab命令中，使用 fprintf 将所需信息写入 stderr 。这可以分离代码输出从Matlab的标题行。


• 回到Python，使用 Popen.communicate（）捕获 stderr 输出。


• 异常 ValueError 处理Matlab的退出事件（ p 已关闭） 。

• Changed the Python command to subprocess.Popen, which allows stderr piping.
• In Matlab command, use fprintf to write wanted info into stderr. This can separate code ouput from Matlab's header lines.
• Back into Python, use Popen.communicate() to catch stderr output.
• The exception ValueError handles exit event of Matlab (p is closed).

编辑：

表示Matlab函数是

say a Matlab function is

function [y, z] = foo(x)
    y = x+1;
    z = x*20;
end

关键是使用 fprintf 抛出输出，而做所有其他事情，你总是做正常在Matlab。

The point is use fprintf to throw the output, while doing all other things as you always do normally in Matlab.

p = subprocess.Popen(['/home/user/Matlab/bin/matlab', '-nodesktop', '-nosplash', '-r "[y, z] = foo(' + str(array) + ');for ii=1:length(y) fprintf(2, \'%d %d\\n\',y(ii),z(ii)); end; exit" >/dev/null'], stdout=subprocess.PIPE, stderr=subprocess.PIPE)

方法2-独立脚本

首先创建一个新的 caller.m 脚本

[y, z] = foo(x);
for ii=1:length(y)
    fprintf(2, '%d %d\n',y(ii),z(ii));
end

注意 x 是从Python调用时赋值的;脚本共享相同的堆栈。

Note that x is to be assigned when calling from Python; scripts share the same stack. (Remember NOT to clear the workspace in the caller script. )

然后，从Python

Then, call the script from Python

p = subprocess.Popen(['/home/user/Matlab/bin/matlab', '-nodesktop', '-nosplash', '-r "x=' + str(array) + ';caller; exit" >/dev/null'], stdout=subprocess.PIPE, stderr=subprocess.PIPE)

将Matlab结果存储在Python变量中

• 当通过 stdout / stderr 管道传递数据时：

  Storing Matlab result in a Python variable

  • When passing data through stdout / stderr pipe:

    请参阅此和 subprocess.check_output（） 。

    Refer to this and subprocess.check_output().

    在处理 double 或二进制文件等严重数据时：

    When handling serious data like double or binary:

    使用Matlab将数据写入外部文件。然后用Python读取这个文件。应该定义一种协议，利用该协议彼此进行双方通话。

    Write the data into an external file with Matlab. Then read this file with Python. A protocol with which both side talk with each other should be defined.

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