Why can't Python execute java.exe via subprocess?

Question

After upgrading Java from 1.6 to 1.7 x64 (on Windows 7), I suddenly can't launch java.exe via Python 2.7's subprocess module anymore. The following script used to just work:

import subprocess
subprocess.check_call([r"C:\Windows\system32\java.exe"])

Now it fails like this:

Traceback (most recent call last):
  File ".\tst.py", line 2, in <module>
    subprocess.check_call([r"C:\Windows\system32\java.exe"])
  File "C:\Python27\lib\subprocess.py", line 506, in check_call
    retcode = call(*popenargs, **kwargs)
  File "C:\Python27\lib\subprocess.py", line 493, in call
    return Popen(*popenargs, **kwargs).wait()
  File "C:\Python27\lib\subprocess.py", line 679, in __init__
    errread, errwrite)
  File "C:\Python27\lib\subprocess.py", line 896, in _execute_child
    startupinfo)
WindowsError: [Error 2] The system cannot find the file specified

I have also confirmed that C:\Windows\system32\java.exe does indeed exist, is an application, and can be executed from the command shell.

What goes wrong here?

EDIT: I've found that I can start C:\Program Files\Java\jre7\bin\java.exe from Python, so C:\Windows\system32\java.exe must be some weird pseudo-shortcut although technically a Windows application. Version 1.7 must've messed it up somehow, since I just confirmed Version 1.6 is fine.

@Marcin According to the file properties the file type is Application (.exe). — aknuds1
– aknuds1, Commented May 11, 2012 at 10:52
If you can investigate a bit more, your edit would make a great answer. If you can't investigate more, consider adding it as an answer anyway. — Marcin
– Marcin, Commented May 11, 2012 at 11:07
@Marcin Gonna submit feedback to Java developers, hopefully they'll get back to me. — aknuds1
– aknuds1, Commented May 11, 2012 at 11:15

grainednoise · Accepted Answer · 2012-05-11 20:03:47Z

9

Assuming that there is a java.exe at "C:\Windows\System32" is not a particularly safe assumption. Even the assumption there is a "C:\Windows\System32" on the system isn't safe: Windows could reside on any fixed drive on the computer.

But even if there is a "C:\Windows\System32\java.exe", this might not be visible for 32-bit processes under Win64. Windows does some interesting things here in the name of backwards compatibility, you might want to look at http://en.wikipedia.org/wiki/WoW64.

Finding the Java version you're looking for - and there can be many - can be a thankless task. If you don't particularly care about which Java you find, try the JAVA_HOME environment variable. It's not always there, but if it is, you're done and it's probably the most portable way of finding a JVM. If it's not there, you can't go wrong by setting it, and many Java applications can make use of that variable.

Then again, Java just might be on the PATH, in which case removing the everything but 'java' in the subprocess call will do the trick. It can't hurt to try.

answered May 11, 2012 at 20:03

grainednoise

2611 silver badge1 bronze badge

Sign up to request clarification or add additional context in comments.

4 Comments

aknuds1 Over a year ago

The reason C:\Windows\system32\java.exe was relevant to me is that it is how I usually find java.exe via PATH, I don't directly rely on that executable path. But you may well be onto something regarding WoW64, I will investigate, thanks.

aknuds1 Over a year ago

You were onto something. False is printed when executing the following with 32-bit Python, but True for 64-bit Python: python.exe -c "import os.path; print os.path.exists(r'C:\windows\system32\java.exe')". Apparently 32-bit apps on 64-bit Windows are redirected from C:\Windows\System32 to C:\Windows\SysWOW64, where there is no java.exe.

notbad.jpeg Over a year ago

Why isn't this one of the top voted of all time answers on SO?

dotz Over a year ago

I also hit this bug. For me, directly using path "C:\Program Files\Java\jre7\bin\java.exe" worked (64-bit, 1.7.0_67-b01). Using just "java" (from the PATH) returned no output even if I issued a legitimate command with subprocess.check_output(...)

Toby · Accepted Answer · 2013-07-29 12:47:05Z

You might also want to check if the PATH environment variable has quotation marks "" around the jre's bin path. Python doesn't seem to like them:

    C:\bin>set PATH=C:\Python27;c:\Program Files\Java\jdk1.6.0_35\bin

    C:\bin>python -c "import subprocess; subprocess.Popen(['java', '-version'], stderr=subprocess.PIPE)"

    C:\bin>set PATH=C:\Python27;"c:\Program Files\Java\jdk1.6.0_35\bin"

    C:\bin>python -c "import subprocess; subprocess.Popen(['java', '-version'], stderr=subprocess.PIPE)"
    Traceback (most recent call last):
    [...]
    WindowsError: [Error 2] The system cannot find the file specified

    C:\bin>

Collectives™ on Stack Overflow

Why can't Python execute java.exe via subprocess?

2 Answers 2

4 Comments

Comments

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

4 Comments

Comments

Related