How can I pass file names to external commands executed from Python?

Question

I am trying to execute a command inside a Python script:

import subprocess
output_process = 
   subprocess.Popen("javac -cp C:\Users\MyUsername\Desktop\htmlcleaner-2.2.jar Scrapping_lastfm.java",
                    shell=True, stdout=subprocess.PIPE)

But I am getting an error package org.htmlcleaner does not exist.

If I run the javac command independently, it executes fine..

My current working directry is C:\Users\MyUsername.

Try the env argument to Popen with the PATH key set to the path of your java packages. — agf
– agf, Commented Sep 8, 2011 at 20:39

fabmilo · Accepted Answer · 2011-09-08 21:09:29Z

1

The error is not raised by python but by the java subprocess. Most likely the java machine is not finding some libraries, and that refines the problem to a PATH configuration problem, most likely the variable CLASSPATH has not been set in the environment. to solve :

import shlex

JAVA_COMMAND=r"javac -cp C:\\Users\\MyUsername\\Desktop\\htmlcleaner-2.2.jar Scrapping_lastfm.java"

cmdline = shlex.split(JAVA_COMMAND)

output_process = subprocess.Popen(cmdline,shell=True, stdout=subprocess.PIPE, env={'CLASSPATH':'/path/to/java/packages'})

answered Sep 8, 2011 at 21:09

fabmilo

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3 Comments

RanRag Over a year ago

i tried using env={'CLASSPATH':'C:\\jdk1.6.0_23\\bin'} but now i am getting error javac not recognized as internal program...

agf Over a year ago

Why are you using a raw string and doubling the backslashes?

agf Over a year ago

@RanRag Try this version or my version with the full path to javac or also set the PATH variable to point to that path.

agf · Accepted Answer · 2011-09-08 21:04:53Z

1

Try

output_process = subprocess.Popen(["javac", "-cp", 
    "C:\Users\MyUsername\Desktop\htmlcleaner-2.2.jar", "Scrapping_lastfm.java"],
    shell=True, stdout=subprocess.PIPE, env={'ENVIRONMENTAL': '/variables/here'})

with whatever java-related environmental variables you have when you run javac normally as items in the env dictionary. asgs suggests you need CLASSPATH.

You don't have to split the command up into a list I just did that to make it easier to see the whole thing.

edited Sep 8, 2011 at 21:04

answered Sep 8, 2011 at 20:59

agf

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2 Comments

asgs Over a year ago

I think it has to be CLASSPATH.

agf Over a year ago

Makes sense. I've rephrased and added that.

rumpel · Accepted Answer · 2011-09-08 21:03:46Z

0

Be aware, that you have to escape the backslash (\) in the string. Your example is fine, however if your username is not actually MyUsername but maybe „nerd“ or any other string forming a valid escape-sequence, the command will fail. Also make sure that you don't have spaces in the filename (or use the split syntax in the other example).

So you might want to do:

output_process = subprocess.Popen(["javac", "-cp", 
    "C:\\Users\\MyUsername\\Desktop\\htmlcleaner-2.2.jar", "Scrapping_lastfm.java"],
    shell=True, stdout=subprocess.PIPE)

answered Sep 8, 2011 at 21:03

rumpel

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