On Tuesday, April 4, 2017 at 5:27:42 PM UTC+2, cassiope wrote: > On Tue, 04 Apr 2017 08:01:42 -0700, venkatachalam.19 wrote: > > > Hello All, > > > > I am writing a python code for processing a data obtained from a sensor. > > The data from sensor is obtained by executing a python script. The data > > obtained should be further given to another python module where the > > received data is used for adjusting the location of an object. > > > > For achieving this, there is a central bash script, which runs both the > > python modules parallel. Something like: > > > > python a.py & > > python b.py & > > What is going on that two python scripts are needed? Which one generates the > data needed by the bash script?
One python script communicates with an external sensor and receives data. Another script controls a robot. That is based on ROS modules. >From the given code, a.py will be the script generating the data. Both the >modules are independent of each other and so I have written both of them in >different python scripts. > > > I am trying to return the sensor data to the bash .sh file, therefore it > > can be provided to the other script. This, based on the online tutorials > > looks like: > > > > sensor_data=$(python execute_sensor_process.py) & > > Presumably <sensor_data> is simply getting the exit status code from the > python interpreter, not the data, right? > What are you seeing? > I am not getting the exit status (I am not setting or printing return status > in the python script). I need both the scripts running in parallel. Meaning > the sensor will be continuously monitoring the location of the robot and this > data will be used in another python script which controls the robot motion. For now, I am printing the output in the script and as far I understood, this can be assigned to a variable in the bash file from where this file is executed. I am not getting any output in the assigned variable in bash. > > and the sensor_data is assigned by printing the required data in the > > corresponding python script. For example, the data is printed in > > execute_sensor_process.py as follows: > > > > print >>sys.stderr,sens_data > > > > By printing the data onto sys.stderr and assigning a return variable in the > > bash, I am expecting the data to be assigned. > > Assigned to what? Some return variable in bash? What?? > Why not use stdout? Either pipe the data from python directly into a > (possibly modified) bash script, > or into a file which gets read by the bash script. > Yes. As shown in "sensor_data=$(python execute_sensor_process.py) &", the variable sensor_data is assigned to hold the return value from the python script. I was using the stdout. But in some forums for similar problems, it is suggested to print the data to stderr (I really dont know what is the significance). I am unaware of piping the data from python. I will look into this. > > But this is not happening. The sensor data is a dictionary and I like to > > have this data for further analysis. I am not getting the data returned > > from the python script on to the bash variable. > > Bash doesn't have dictionaries like python. Why is bash needed? > Bash is needed to run the different scripts. I tried using multiprocess and thread from python, but really they are not performing parallel processing, when there are completely two different process. I understood it by executing the multiprocess/thread. Sequential operation was happening, which lead to the situation that only one python process is always executed. > > Can someone help me to understand why the code is not working? I tried > > other approaches of function call such as > > You haven't given us enough of the code to really answer. > > > sensor_data=$`python execute_sensor_process.py` & > > > > python execute_sensor_process.py tempfile.txt & > > kinexon_data=`cat tempfile.txt` & > > > > But none of the approaches are working. > > > > Thank you, > > Venkatachalam Srinivasan > > I wonder if you could completely eliminate the bash script - do it all in > python. > I've written quite a few bash scripts, but not so many since I started using > python. Only exception is for low level functions on systems without a > functioning > python. -- https://mail.python.org/mailman/listinfo/python-list
