I cannot figure out how I can execute a python script from my C code. I read that I can embed the python code inside C, but I want simply to launch a python script as if I execute it from command line. I tried with the following code:
char * paramsList[] = {"/bin/bash", "-c", "/usr/bin/python", "/home/mypython.py",NULL};
pid_t pid1, pid2;
int status;
pid1 = fork();
if(pid1 == -1)
{
char err[]="First fork failed";
die(err,strerror(errno));
}
else if(pid1 == 0)
{
pid2 = fork();
if(pid2 == -1)
{
char err[]="Second fork failed";
die(err,strerror(errno));
}
else if(pid2 == 0)
{
int id = setsid();
if(id < 0)
{
char err[]="Failed to become a session leader while daemonising";
die(err,strerror(errno));
}
if (chdir("/") == -1)
{
char err[]="Failed to change working directory while daemonising";
die(err,strerror(errno));
}
umask(0);
execv("/bin/bash",paramsList); // python system call
}
else
{
exit(EXIT_SUCCESS);
}
}
else
{
waitpid(pid1, &status, 0);
}
I don't know where the error is since if I replace the call to python script with the call to another executable, it works well.
I have added at the beginning of my python script the line:
#!/usr/bin/python
What can I do?
Thank you in advance
From the Bash man page:
-c string If the -c option is present, then commands are read
from string. If there are arguments after the string,
they are assigned to the positional parameters,
starting with $0.
E.g.
$ bash -c 'echo x $0 $1 $2' foo bar baz
x foo bar baz
You, however don’t want to assign to the positional parameters, so change your paramList to
char * paramsList[] = { "/bin/bash", "-c",
"/usr/bin/python /home/mypython.py", NULL };
Using char * paramsList[] = {"/usr/bin/python", "/tmp/bla.py",NULL}; and execv("/usr/bin/python",paramsList); // python system call caused a successful invocation of the python script named bla.py
Related
I can call a python script in C# and redirect the output/error using the following code:
using System.Diagnostics;
namespace ConsoleApplication1
{
class Program
{
static void Main(string[] args)
{
// Configure new process
Process cmd = new Process();
cmd.StartInfo.FileName = "python.exe";
cmd.StartInfo.Arguments = "<PYTHON FILE>";
cmd.StartInfo.RedirectStandardInput = true;
cmd.StartInfo.RedirectStandardOutput = true;
cmd.StartInfo.RedirectStandardError = true;
cmd.StartInfo.CreateNoWindow = true;
cmd.StartInfo.UseShellExecute = false;
cmd.StartInfo.WorkingDirectory = "<PATH TO WORKING DIRECTORY>";
string stdout, stderr;
// Start process and wait for the process to exit
cmd.Start();
cmd.StandardInput.WriteLine();
cmd.StandardInput.Flush();
cmd.StandardInput.Close();
cmd.WaitForExit();
stderr = cmd.StandardError.ReadToEnd();
stdout = cmd.StandardOutput.ReadToEnd();
// Check for error
if (!string.IsNullOrEmpty(stderr))
{
Console.WriteLine(stderr);
}
else
{
Console.WriteLine(stdout);
}
}
}
}
I have been trying to debug the python file using the following:
using System.Diagnostics;
namespace ConsoleApplication1
{
class Program
{
static void Main(string[] args)
{
// Configure new process
Process cmd = new Process();
cmd.StartInfo.FileName = "python.exe";
cmd.StartInfo.Arguments = "-mpdb <PYTHON FILE>";
cmd.StartInfo.RedirectStandardInput = true;
cmd.StartInfo.RedirectStandardOutput = true;
cmd.StartInfo.RedirectStandardError = true;
cmd.StartInfo.CreateNoWindow = true;
cmd.StartInfo.UseShellExecute = false;
cmd.StartInfo.WorkingDirectory = "<PATH TO WORKING DIRECTORY>";
string stdin = "", stdout, stderr;
cmd.Start();
while (true)
{
// This works the first iteration, but throws a 'Cannot write to a closed TextWriter' error on the following iteration
// But I need to close the StandardInput in order to get the output from the process (stdout/stderr)
cmd.StandardInput.WriteLine(stdin);
cmd.StandardInput.Flush();
cmd.StandardInput.Close();
cmd.WaitForExit();
stderr = cmd.StandardError.ReadToEnd();
stdout = cmd.StandardOutput.ReadToEnd();
// Check if the CMD was valid
if (!string.IsNullOrEmpty(stderr))
{
Console.WriteLine(stderr);
}
else
{
Console.WriteLine(stdout);
}
stdin = Console.ReadLine();
if (string.IsNullOrEmpty(stdin)) break;
}
cmd.WaitForExit();
}
}
}
I am sort of in a catch-22 problem where I want stdin to remain open so I can feed more commands to the python/pdb process (i.e. 'step', 'next', 'continue'...), but in order to get stdout or stderr I need to close and wait. Calling cmd.Start(); multiple times does not work because that just restarts the process using the same StartInfo.FileName and StartInfo.Arguments.
Am I going about this the wrong way or is there something trivial that I have missed in the documentation? Thanks in advance.
I made a Linux background process (in c++) that monitors a directory and attempts to launch a Python script if a certain file appears in that directory. My issue is that the child process responsible for launching the Python script exits immediately after the execvp function is called and I can't understand why. All of the necessary files are under root's ownership. Here is my code if it helps. Thank you in advance for any pointers! I have marked the error in my code where the error occurs. I have also included the Python script to be called
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/wait.h>
#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
using namespace std;
char* arguments[3];
FILE* fd;
const char* logFilePath = "/home/BluetoothProject/Logs/fileMonitorLogs.txt";
char* rfcommPath = (char*)"/home/BluetoothProject/RFCOMMOut.py";
void logToFile(const char*);
void doWork();
void logToFile(const char* str) {
fd = fopen(logFilePath, "a");
fprintf(fd, "%s\n", str);
fclose(fd);
}
int main() {
arguments[0] = (char*)"python";
arguments[1] = rfcommPath;
arguments[2] = NULL;
pid_t pid = fork();
if(pid < 0) {
printf("Fork failed");
exit(1);
} else if(pid > 0) {
exit(EXIT_SUCCESS);
}
umask(0);
pid_t sid = setsid();
if(sid < 0) {
logToFile("setsid() didn't work.");
exit(1);
}
if ((chdir("/")) < 0) {
logToFile("chdir() didn't work.");
exit(EXIT_FAILURE);
}
close(STDIN_FILENO);
close(STDOUT_FILENO);
close(STDERR_FILENO);
doWork();
}
void doWork() {
pid_t pid = fork();
if(pid < 0) {
logToFile("doWork() fork didn't work.");
} else if(pid > 0) {
int status = 0;
waitpid(pid, &status, 0);
if(WEXITSTATUS(status) == 1) {
logToFile("Child process exited with an error.");
}
} else {
int error = execvp(arguments[0], arguments); //Here is where the error is
if(error == -1) {
logToFile("execvp() failed.");
}
exit(1);
}
}
Python script (AKA RFCOMMOut.py)
import RPi.GPIO as gpio
import serial
led_state = 0
led_pin = 11
gpio.setmode(gpio.BOARD)
gpio.setwarnings(False)
gpio.setup(led_pin, gpio.OUT)
try:
ser = serial.Serial(port = '/dev/rfcomm0',
baudrate = 9600,
parity = serial.PARITY_NONE,
stopbits = serial.STOPBITS_ONE,
bytesize = serial.EIGHTBITS)
except IOException as e:
logFile = open("/home/BluetoothProject/Logs/fileMonitorLogs.txt", "a")
logFile.write("(First error handler) There was an exception:\n")
logFile.write(str(e))
logFile.write("\n")
logFile.close()
#gpio.output
def process_input(input):
global led_state
if input == "I have been sent.\n":
if led_state == 1:
led_state = 0
gpio.output(led_pin, led_state)
else:
led_state = 1
gpio.output(led_pin, led_state)
while True:
try:
transmission = ser.readline()
process_input(transmission)
except IOError as e:
logFile = open("/home/BluetoothProject/Logs/fileMonitorLogs.txt", "a")
logFile.write("(second error handler) There was an exception:\n")
logFile.write(str(e))
logFile.write("\n")
logFile.close()
break
led_state = 0
gpio.output(led_pin, led_state)
gpio.cleanup()
print("End of program\n")
The question is a little unclear, so I'll try to take a few different educated guesses at what the problem is and address each one individually.
TL;DR: Remove close(STDOUT_FILENO) and close(STDERR_FILENO) to get more debugging information which will hopefully point you in the right direction.
execvp(3) is returning -1
According to the execvp(3) documentation, execvp(3) sets errno when it fails. In order to understand why it is failing, your program will need to output the value of errno somewhere; perhaps stdout, stderr, or your log file. A convenient way to do this is to use perror(3). For example:
#include <stdio.h>
...
void doWork() {
...
} else {
int error = execvp(arguments[0], arguments);
if(error == -1) {
perror("execvp() failed");
}
}
...
}
Without knowing what that errno value is, it will be difficult to identify why execvp(3) is failing.
execvp(3) is succeeding, but my Python program doesn't appear run
execvp(3) succeeding means that the Python interpreter has successfully been invoked (assuming that there is no program in your PATH that is named "python", but is not actually a Python interpreter). If your program doesn't appear to be running, that means Python is having difficulty loading your program. To my knowledge, Python will always output relevant error messages in this situation to stderr; for example, if Python cannot find your program, it will output "No such file or directory" to stderr.
However, it looks like your C program is calling close(STDERR_FILENO) before calling doWork(). According to fork(2), child processes inherit copies of their parent's set of open file descriptors. This means that calling close(STDERR_FILENO) before forking will result in the child process not having an open stderr file descriptor. If Python is having any errors executing your program, you'll never know, since Python is trying to notify you through a file descriptor that doesn't exist. If execvp(3) is succeeding and the Python program appears to not run at all, then I recommend you remove close(STDERR_FILENO) from your C program and run everything again. Without seeing the error message output by Python, it will be difficult to identify why it is failing to run the Python program.
As an aside, I recommend against explicitly closing stdin, stdout, and stderr. According to stdin(3), the standard streams are closed by a call to exit(3) and by normal program termination.
execvp(3) is succeeding, my Python program is running, but my Python program exits before it does any useful work
In this case, I'm not sure what the problem might be, since I'm not very familiar with Raspberry Pi. But I think you'll have an easier time debugging if you don't close the standard streams before running the Python program.
Hope this helps.
I'm writing my first VSCode extension. In short, the extension opens a terminal (PowerShell) and executes a command:
term = vscode.window.activeTerminal;
term.sendText("ufs put C:\\\Users\\<userID>\\AppData\\Local\\Programs\\Python\\Python38-32\\Lib\\site-packages\\mymodule.py");
After selecting a Python environment, VSCode should know where Python is located (python.pythonPath). But the path to Python will obviously vary depending on the Python installation, version and so on. So I was hoping that I could do something like:
term.sendText("ufs put python.pythonPath\\Lib\\site-packages\\mymodule.py");
But how can I do this in my extension (TypeScript)? How do I refer to python.pythonPath?
My configuration:
Windows 10
Python 3.8.2
VSCode 1.43.2
Microsofts Python extension 2020.3.69010
Node.js 12.16.1
UPDATE:
Nathan, thank you for your comment. I used a child process as suggested. It executes a command to look for pip. Relying on the location of pip is not bullet proof, but it works for now:
var pwd = 'python.exe -m pip --version';
const cp = require('child_process');
cp.exec(pwd, (err, stdout, stderr) => {
console.log('Stdout: ' + stdout);
console.log('Stderr: ' + stderr);
if (err) {
console.log('error: ' + err);
}
});
Not sure where to go from here to process stdout, but I tried child_process.spawn using this accepted answer:
function getPath(cmd, callback) {
var spawn = require('child_process').spawn;
var command = spawn(cmd);
var result = '';
command.stdout.on('data', function (data) {
result += data.toString();
});
command.on('close', function (code) {
return callback(result);
});
}
let runCommand = vscode.commands.registerCommand('extension.getPath', function () {
var resultString = getPath("python.exe -m pip --version", function (result) { console.log(result) });
console.log(resultString);
});
Hopefully, this would give me stdout as a string. But the only thing I got was undefined. I'm way beyond my comfort zone now. Please advise me how to proceed.
I'd like to run the following shell command 10 times
./file.py 1111x
with the 'x' ranging from 0 to 9
i.e. a different port for each .file.py file. I need each instance running in its own shell. I already tried creating a batch file and a python script that calls the windows shell but both without success.
What about this...
import os
import subprocess
for x in range(0,10):
command = './file.py 1111' + str(x)
os.system(command)
#or
subprocess.call('cmd ' + command, shell=True)
What you're looking for is a powershell job. You may need to tweak this a bit to accommodate your specific requirements, but this should do what you need.
[ScriptBlock]$PyBlock = {
param (
[int]$x,
[string]$pyfile
)
try {
[int]$Port = (11110 + $x)
python $pyfile $Port
}
catch {
Write-Error $_
}
}
try {
0..9 | ForEach-Object {
Start-Job -Name "PyJob $_" -ScriptBlock $PyBlock -ArgumentList #($_, 'path/to/file.py')
}
Get-Job | Wait-Job -Timeout <int>
#If you do not specify a timeout then it will wait indefinitely.
#If you use -Timeout then make sure it's long enough to accommodate the runtime of your script.
Get-Job | Receive-Job
}
catch {
throw $_
}
I want to call a Python script from C, passing some arguments that are needed in the script.
The script I want to use is mrsync, or multicast remote sync. I got this working from command line, by calling:
python mrsync.py -m /tmp/targets.list -s /tmp/sourcedata -t /tmp/targetdata
-m is the list containing the target ip-addresses.
-s is the directory that contains the files to be synced.
-t is the directory on the target machines where the files will be put.
So far I managed to run a Python script without parameters, by using the following C program:
Py_Initialize();
FILE* file = fopen("/tmp/myfile.py", "r");
PyRun_SimpleFile(file, "/tmp/myfile.py");
Py_Finalize();
This works fine. However, I can't find how I can pass these argument to the PyRun_SimpleFile(..) method.
Seems like you're looking for an answer using the python development APIs from Python.h. Here's an example for you that should work:
#My python script called mypy.py
import sys
if len(sys.argv) != 2:
sys.exit("Not enough args")
ca_one = str(sys.argv[1])
ca_two = str(sys.argv[2])
print "My command line args are " + ca_one + " and " + ca_two
And then the C code to pass these args:
//My code file
#include <stdio.h>
#include <python2.7/Python.h>
void main()
{
FILE* file;
int argc;
char * argv[3];
argc = 3;
argv[0] = "mypy.py";
argv[1] = "-m";
argv[2] = "/tmp/targets.list";
Py_SetProgramName(argv[0]);
Py_Initialize();
PySys_SetArgv(argc, argv);
file = fopen("mypy.py","r");
PyRun_SimpleFile(file, "mypy.py");
Py_Finalize();
return;
}
If you can pass the arguments into your C function this task becomes even easier:
void main(int argc, char *argv[])
{
FILE* file;
Py_SetProgramName(argv[0]);
Py_Initialize();
PySys_SetArgv(argc, argv);
file = fopen("mypy.py","r");
PyRun_SimpleFile(file, "mypy.py");
Py_Finalize();
return;
}
You can just pass those straight through. Now my solutions only used 2 command line args for the sake of time, but you can use the same concept for all 6 that you need to pass... and of course there's cleaner ways to capture the args on the python side too, but that's just the basic idea.
Hope it helps!
You have two options.
Call
system("python mrsync.py -m /tmp/targets.list -s /tmp/sourcedata -t /tmp/targetdata")
in your C code.
Actually use the API that mrsync (hopefully) defines. This is more flexible, but much more complicated. The first step would be to work out how you would perform the above operation as a Python function call. If mrsync has been written nicely, there will be a function mrsync.sync (say) that you call as
mrsync.sync("/tmp/targets.list", "/tmp/sourcedata", "/tmp/targetdata")
Once you've worked out how to do that, you can call the function directly from the C code using the Python API.