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Run Python app (script on PATH) from Java

I'm facing quite simple problem, yet still not able to figure out what in particular causes that, and - more importantly - how to solve it.
I'm currently on Linux, and I would like to run an python app (script) from a Java application. The script is on PATH, thus I really would like to utilise that (avoid using absolute path to the script), if possible.
However, all I tried resulted in various forms of "File does not exist".
Sample
As a demonstration, I've tried to run one python3-based app (meld)
and one binary-built app (ls) for comparison:
$ which ls
/usr/bin/ls
$ file /usr/bin/ls
/usr/bin/ls: ELF 64-bit LSB shared object, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, BuildID[sha1]=[...], for GNU/Linux 3.2.0, stripped
$ which meld
/usr/bin/meld
$ file /usr/bin/meld
/usr/bin/meld: Python script, UTF-8 Unicode text executable
$ head -n1 /usr/bin/meld
#!/usr/bin/python3
Nextly, I've created simple Java main, which tries several ways how to start theese:
package cz.martlin.processes;
import java.io.File;
import java.io.IOException;
import java.lang.ProcessBuilder.Redirect;
import java.util.List;
import java.util.stream.Collectors;
public class ProcessPlaying {
public static void main(String[] args) {
List<List<String>> commands = List.of(
List.of("ls"),
List.of("/usr/bin/ls"),
List.of("meld"),
List.of("/usr/bin/meld"),
List.of("python3", "/usr/bin/meld"),
List.of("/usr/bin/python3", "/usr/bin/meld"),
List.of("sh", "-c", "meld"),
List.of("sh", "-c", "/usr/bin/meld"),
List.of("sh", "-c", "python3 /usr/bin/meld")
);
for (List<String> command : commands) {
run(command);
}
}
private static void run(List<String> command) {
System.out.println("Running: " + command);
//String executable = command.get(0);
//boolean exists = new File(executable).exists();
//System.out.println("Exists the " + executable + " ? " + exists);
try {
ProcessBuilder pb = new ProcessBuilder(command);
pb.redirectError(Redirect.INHERIT);
Process proc = pb.start();
// Process proc = Runtime.getRuntime().exec(command.stream().collect(Collectors.joining(" ")));
int code = proc.waitFor();
System.out.println("OK, return code: " + code);
} catch (IOException e) {
System.out.println("Failed to start: " + e.toString());
} catch (InterruptedException e) {
System.out.println("Failed to await: " + e.toString());
}
System.out.println();
}
}
Here are the results:
Running: [ls]
OK, return code: 0
Running: [/usr/bin/ls]
OK, return code: 0
Running: [meld]
Failed to start: java.io.IOException: Cannot run program "meld": error=2, Directory or file doesn't exist
Running: [/usr/bin/meld]
Failed to start: java.io.IOException: Cannot run program "/usr/bin/meld": error=2, Directory or file doesn't exist
Running: [python3, /usr/bin/meld]
python3: can't open file '/usr/bin/meld': [Errno 2] No such file or directory
OK, return code: 2
Running: [/usr/bin/python3, /usr/bin/meld]
/usr/bin/python3: can't open file '/usr/bin/meld': [Errno 2] No such file or directory
OK, return code: 2
Running: [sh, -c, meld]
sh: line 1: meld: command not found
OK, return code: 127
Running: [sh, -c, /usr/bin/meld]
sh: line 1: /usr/bin/meld: Directory or file doesn't exist
OK, return code: 127
Running: [sh, -c, python3 /usr/bin/meld]
python3: can't open file '/usr/bin/meld': [Errno 2] No such file or directory
OK, return code: 2
To sum it up:
all of the commands tried works when executed directly from the shell (either sh or bash)
executing the binary works either by the full path (/usr/bin/ls) or by just the name (ls)
executing the python script the same way doesn't work neither way
when trying to run the python3 interpreter and populate the script path as an argument to the python, now the python yields the script file doesn't exist
trying to populate it as a command to the brand new shell didn't help either
I've tried to use the Runtime#exec (based on this comment: https://stackoverflow.com/a/36783743/3797793) to start the process (both the exec(String) and exec(String[] forms), but no sucess (none of the listed commands did actually execute).
Thus, my question is/are:
What do I understand wrong?
How to start the Python script from Java?
Would some small (ba)sh script wrapper do the job?
Since it's python3-based, Jython wouldn't help here (because the latest one is 2.7.*), would it?
Further requirements:
As mentioned, I would like to be able to avoid using full path to the Python script
Also, I would like to have platform independant solution (at least Linux and Windows compatible)
Thanks in advance

make a python program have my UID to modificate a file

So, in short, I created a script (named main.py) in which there was a moment where I wrote in a file. It worked well. However, the permissions on this file had to be rwxrwxrw- and hence anyone could modify the file on the server. That's not what I wanted. So I changed the permissions to rwxrwxr-- and then I changed the code of main.py :
#!/usr/bin/python
import subprocess
text = "I want this text to appear in my file"
command = subprocess.Popen(["python", "modificateFile.py", str('"')+text+str('"')], stderr=subprocess.PIPE, stdout=subprocess.PIPE) #I run another file that will do the task
for i in command.stderr:
print(i.decode("utf-8")) #check if there is any error
code of modificateFile.py
#!/usr/bin/python
import platform
import os
import sys
UID = 1080 #my UID.. I don't really know if it's the right way to program this
if __name__ == "__main__":
system = platform.system()
if system == "Linux": #ok it may be useless
os.setuid(UID) # /!\ I THINK THAT'S WHERE THE PROBLEM IS /!\
if len(sys.argv) > 1:
with open("file.txt", "w", encoding="utf-8") as f:
f.write(sys.argv[1])
else:
sys.stderr.write("not enough parameters to work") #didn't know which error I could raise..
#so as I already imported sys, I used this function
exit(-1)
else:
sys.stderr.write("wrong OS : program only work on linux")
exit(-1)
When I created this, I didn't know really what I was doing to be honest… I am learning programming.
Error message:
Traceback (most recent call last): File "modificateFile.py", line 11,
in os.setuid(UID) PermissionError: [Errno 1] Operation not permitted
I heard of SUID.. but I don't have root permissions.
Could someone explain what is wrong and what I could do ?
(if you need more elements, tell me it)

ok…. I thought SUID was only available for root programs… I had already tested it for this program but it didn't work. However, I learnt after that SUID is not available for programs with a shebang at the beginning… So, I created a code in C to do that.

Subprocess.Popen only runs second time

I have a boot controller which runs a boot.py file contained in each folder of each tool i am trying to deploy. I want my boot controller to run all of these boot files simultaneously. The config file has the tool names and the versions desired, which help to generate the path to the boot.py.
def run_boot():
config_file = get_config_file()
parse_config_file.init(config_file)
tools = parse_config_file.get_tools_to_deploy()
#tools is now a list of tool names
top_dir = os.getcwd()
for tool in tools:
ver = parse_config_file.get_tool_version(tool).strip()
boot_file_path = "{0}\\Deploy\\{1}\\{2}".format(os.getcwd(),tool,ver)
try:
subprocess.Popen('boot.py', shell=True, cwd=boot_file_path)
except:
print ("{0} failed to open".format(tool))
print(tool, boot_file_path)
os.chdir(top_dir)
The first time i run this, the print(tool, boot_file_path) executes but the processes do not. the second time it is run the processes do open. I cannot find a reason for this.

FileNotFoundError When file exists (when created in current script)

I am trying to create a secure (e.g., SSL/HTTPS) XML-RPC Client Server. The client-server part works perfectly when the required certificates are present on my system; however, when I try to create the certificates during execution, I receive a FileNotFoundError when opening the ssl-wrapped socket even though the certificates are clearly present (because the preceding function created them.)
Why is the FileNotFoundError given when the files are present? (If I simply close and restart the python script no error is produced when opening the socket and everything works with no issue whatsoever.)
I've searched elsewhere for solutions, but the best/closest answer I've found is, perhaps, "race conditions" between creating the certificates and opening them. However, I've tried adding "sleep" to alleviate the possibility of race conditions (as well as running each function individually via a user input menu) with the same error every time.
What I am missing?
Here is a snippet of my code:
import os
import threading
import ssl
from xmlrpc.server import SimpleXMLRPCServer
import certs.gencert as gencert # <---- My python module for generating certs
...
rootDomain = "mydomain"
CERTFILE = "certs/mydomain.cert"
KEYFILE = "certs/mydomain.key"
...
def listenNow(ipAdd, portNum, serverCert, serverKey):
# Create XMLRPC Server, based on ipAdd/port received
server = SimpleXMLRPCServer((ipAdd, portNum))
# **THIS** is what causes the FileNotFoundError ONLY if
# the certificates are created during THE SAME execution
# of the program.
server.socket = ssl.wrap_socket(server.socket,
certfile=serverCert,
keyfile=serverKey,
do_handshake_on_connect=True,
server_side=True)
...
# Start server listening [forever]
server.serve_forever()
...
# Verify Certificates are present; if not present,
# create new certificates
def verifyCerts():
# If cert or key file not present, create new certs
if not os.path.isfile(CERTFILE) or not os.path.isfile(KEYFILE):
# NOTE: This [genert] will create certificates matching
# the file names listed in CERTFILE and KEYFILE at the top
gencert.gencert(rootDomain)
print("Certfile(s) NOT present; new certs created.")
else:
print("Certfiles Verified Present")
# Start a thread to run server connection as a daemon
def startServer(hostIP, serverPort):
# Verify certificates present prior to starting server
verifyCerts()
# Now, start thread
t = threading.Thread(name="ServerDaemon",
target=listenNow,
args=(hostIP,
serverPort,
CERTFILE,
KEYFILE
)
)
t.daemon = True
t.start()
if __name__ == '__main__':
startServer("127.0.0.1", 12345)
time.sleep(60) # <--To allow me to connect w/client before closing
When I run the above, with NO certificates present, this is the error I receive:
$ python3 test.py
Certfile(s) NOT present; new certs created.
Exception in thread ServerDaemon:
Traceback (most recent call last):
File "/usr/lib/python3.5/threading.py", line 914, in _bootstrap_inner
self.run()
File "/usr/lib/python3.5/threading.py", line 862, in run
self._target(*self._args, **self._kwargs)
File "test.py", line 41, in listenNow
server_side=True)
File "/usr/lib/python3.5/ssl.py", line 1069, in wrap_socket
ciphers=ciphers)
File "/usr/lib/python3.5/ssl.py", line 691, in __init__
self._context.load_cert_chain(certfile, keyfile)
FileNotFoundError: [Errno 2] No such file or directory
When I simply re-run the script a second time (i.e., the cert files are already present when it starts, everything runs as expected with NO errors, and I can connect my client just fine.
$ python3 test.py
Certfiles Verified Present
What is preventing the ssl.wrap_socket function from seeing/accessing the files that were just created (and thus producing the FileNotFoundError exception)?
EDIT 1:
Thanks for the comments John Gordon. Here is a copy of gencert.py, courtesy of Atul Varm, found here https://gist.github.com/toolness/3073310
import os
import sys
import hashlib
import subprocess
import datetime
OPENSSL_CONFIG_TEMPLATE = """
prompt = no
distinguished_name = req_distinguished_name
req_extensions = v3_req
[ req_distinguished_name ]
C = US
ST = IL
L = Chicago
O = Toolness
OU = Experimental Software Authority
CN = %(domain)s
emailAddress = varmaa#toolness.com
[ v3_req ]
# Extensions to add to a certificate request
basicConstraints = CA:FALSE
keyUsage = nonRepudiation, digitalSignature, keyEncipherment
subjectAltName = #alt_names
[ alt_names ]
DNS.1 = %(domain)s
DNS.2 = *.%(domain)s
"""
MYDIR = os.path.abspath(os.path.dirname(__file__))
OPENSSL = '/usr/bin/openssl'
KEY_SIZE = 1024
DAYS = 3650
CA_CERT = 'ca.cert'
CA_KEY = 'ca.key'
# Extra X509 args. Consider using e.g. ('-passin', 'pass:blah') if your
# CA password is 'blah'. For more information, see:
#
# http://www.openssl.org/docs/apps/openssl.html#PASS_PHRASE_ARGUMENTS
X509_EXTRA_ARGS = ()
def openssl(*args):
cmdline = [OPENSSL] + list(args)
subprocess.check_call(cmdline)
def gencert(domain, rootdir=MYDIR, keysize=KEY_SIZE, days=DAYS,
ca_cert=CA_CERT, ca_key=CA_KEY):
def dfile(ext):
return os.path.join('domains', '%s.%s' % (domain, ext))
os.chdir(rootdir)
if not os.path.exists('domains'):
os.mkdir('domains')
if not os.path.exists(dfile('key')):
openssl('genrsa', '-out', dfile('key'), str(keysize))
# EDIT 3: mydomain.key gets output here during execution
config = open(dfile('config'), 'w')
config.write(OPENSSL_CONFIG_TEMPLATE % {'domain': domain})
config.close()
# EDIT 3: mydomain.config gets output here during execution
openssl('req', '-new', '-key', dfile('key'), '-out', dfile('request'),
'-config', dfile('config'))
# EDIT 3: mydomain.request gets output here during execution
openssl('x509', '-req', '-days', str(days), '-in', dfile('request'),
'-CA', ca_cert, '-CAkey', ca_key,
'-set_serial',
'0x%s' % hashlib.md5(domain +
str(datetime.datetime.now())).hexdigest(),
'-out', dfile('cert'),
'-extensions', 'v3_req', '-extfile', dfile('config'),
*X509_EXTRA_ARGS)
# EDIT 3: mydomain.cert gets output here during execution
print "Done. The private key is at %s, the cert is at %s, and the " \
"CA cert is at %s." % (dfile('key'), dfile('cert'), ca_cert)
if __name__ == "__main__":
if len(sys.argv) < 2:
print "usage: %s <domain-name>" % sys.argv[0]
sys.exit(1)
gencert(sys.argv[1])
EDIT 2:
Regarding John's comment, "this might mean that those files are being created, but not in the directory [I] expect":
When I have the directory open in another window, I see the files pop up in the correct location during execution. In addition, when running the test.py script a second time with no changes, the files are identified as present in the correct (the same) location. This leads me to believe that file location is not the problem. Thanks for the suggestion. I'll keep looking.
EDIT 3:
I stepped through the gencert.py program, and each of the files are correctly output at the right time during execution. I indicated when exactly they were output within the above file, labeled with "EDIT 3"
While gencert is paused awaiting my input (raw_input), I can open/view/edit the mentioned files in another program with no problem.
In addition, with the first test.py instance running (paused, waiting for user input, just after mydomain.cert appears), I can run a second instance of test.py in another terminal and it sees/uses the files just fine.
Within the first instance, however, if I continue the program it outputs "FileNotFoundError."

The problem contained in the above stems from the use of os.chdir(rootdir) as suggested by John; however, the specifics are slightly different than the created files being in the wrong location. The problem is the current working directory (cwd) of the running program being changed by gencert(). Here are the specifics:
The program is started with test.py, which calls verifyCerts(). At this point the program is running in the current directory of whichever folder test.py is running inside of. Use os.getcwd() to find the current directory at this point. In this case (as an example), it is running in:
/home/name/testfolder/
Next, os.path.isfile() looks for the files "certs/mydomain.cert" and "certs/mydomain.key"; based on the file path above [e.g., the cwd], it is looking for the following files:
/home/name/testfolder/certs/mydomain.cert
/home/name/testfolder/certs/mydomain.key
The above files are not present, so the program executes gencert.gencert(rootDomain) which correctly creates both files as expected in the exact locations mentioned above in number 2.
The problem is indeed the os.chdir() call: When gencert() executes, it uses os.chdir() to change the cwd to "rootdir," which is os.path.abspath(os.path.dirname(__file__)), which is the directory of the current file (gencert.py). Since this file is located a folder deeper, the new cwd becomes:
/home/name/testfolder/certs/
When gencert() finishes execution and the control returns to test.py, the cwd never changes again; the cwd remains as /home/name/testfolder/certs/ even when execution returns to test.py.
Later, when ssl.wrap_socket() tries to find the serverCert and serverKey, it looks for "certs/mydomain.cert" and "certs/mydomain.key" in the cwd, so here is the full path of what it is looking for:
/home/name/testfolder/certs/certs/mydomain.cert
/home/name/testfolder/certs/certs/mydomain.key
These two files are NOT present, so the program correctly returns "FileNotFoundError".
Solution
A) Move the "gencert.py" file to the same directory as "test.py"
B) At the beginning of "gencert.py" add cwd = os.getcwd() to record the original cwd of the program; then, at the very end, add os.chdir(cwd) to change back to the original cwd before ending and giving control back to the calling program.
I went with option 'B', and my program now works flawlessly. I appreciate the assistance from John Gordon to point me toward finding the source of my problem.

Python - How do you run a .py file?

I've looked all around Google and its archives. There are several good articles, but none seem to help me out. So I thought I'd come here for a more specific answer.
The Objective: I want to run this code on a website to get all the picture files at once. It'll save a lot of pointing and clicking.
I've got Python 2.3.5 on a Windows 7 x64 machine. It's installed in C:\Python23.
How do I get this script to "go", so to speak?
=====================================
WOW. 35k views. Seeing as how this is top result on Google, here's a useful link I found over the years:
http://learnpythonthehardway.org/book/ex1.html
For setup, see exercise 0.
=====================================
FYI: I've got zero experience with Python. Any advice would be appreciated.
As requested, here's the code I'm using:
"""
dumpimages.py
Downloads all the images on the supplied URL, and saves them to the
specified output file ("/test/" by default)
Usage:
python dumpimages.py http://example.com/ [output]
"""
from BeautifulSoup import BeautifulSoup as bs
import urlparse
from urllib2 import urlopen
from urllib import urlretrieve
import os
import sys
def main(url, out_folder="C:\asdf\"):
"""Downloads all the images at 'url' to /test/"""
soup = bs(urlopen(url))
parsed = list(urlparse.urlparse(url))
for image in soup.findAll("img"):
print "Image: %(src)s" % image
filename = image["src"].split("/")[-1]
parsed[2] = image["src"]
outpath = os.path.join(out_folder, filename)
if image["src"].lower().startswith("http"):
urlretrieve(image["src"], outpath)
else:
urlretrieve(urlparse.urlunparse(parsed), outpath)
def _usage():
print "usage: python dumpimages.py http://example.com [outpath]"
if __name__ == "__main__":
url = sys.argv[-1]
out_folder = "/test/"
if not url.lower().startswith("http"):
out_folder = sys.argv[-1]
url = sys.argv[-2]
if not url.lower().startswith("http"):
_usage()
sys.exit(-1)
main(url, out_folder)

On windows platform, you have 2 choices:
In a command line terminal, type
c:\python23\python xxxx.py
Open the python editor IDLE from the menu, and open xxxx.py, then press F5 to run it.
For your posted code, the error is at this line:
def main(url, out_folder="C:\asdf\"):
It should be:
def main(url, out_folder="C:\\asdf\\"):

Usually you can double click the .py file in Windows explorer to run it. If this doesn't work, you can create a batch file in the same directory with the following contents:
C:\python23\python YOURSCRIPTNAME.py
Then double click that batch file. Or, you can simply run that line in the command prompt while your working directory is the location of your script.

Since you seem to be on windows you can do this so python <filename.py>. Check that python's bin folder is in your PATH, or you can do c:\python23\bin\python <filename.py>. Python is an interpretive language and so you need the interpretor to run your file, much like you need java runtime to run a jar file.

use IDLE Editor {You may already have it} it has interactive shell for python and it will show you execution and result.

Your command should include the url parameter as stated in the script usage comments.
The main function has 2 parameters, url and out (which is set to a default value)
C:\python23\python "C:\PathToYourScript\SCRIPT.py" http://yoururl.com "C:\OptionalOutput\"

If you want to run .py files in Windows, Try installing Git bash
Then download python(Required Version) from python.org and install in the main c drive folder
For me, its :
"C:\Python38"
then open Git Bash and go to the respective folder where your .py file is stored :
For me, its :
File Location : "Downloads"
File Name : Train.py
So i changed my Current working Directory From "C:/User/(username)/" to "C:/User/(username)/Downloads"
then i will run the below command
" /c/Python38/python Train.py "
and it will run successfully.
But if it give the below error :
from sklearn.model_selection import train_test_split
ModuleNotFoundError: No module named 'sklearn'
Then Do not panic :
and use this command :
" /c/Python38/Scripts/pip install sklearn "
and after it has installed sklearn go back and run the previous command :
" /c/Python38/python Train.py "
and it will run successfully.
!!!!HAPPY LEARNING !!!!