Tuesday, March 7, 2017

Remote Debugging Python on Eclipse

Remote debugging is extremely useful, especially when you have limited access to the system used to run the application.

Let us call the system where the application is to be run as rsys and the one used to debug as dsys.

Setup dsys :
1. Install eclipse on dsys.

2. Make sure you have the pydev and debug perspectives enabled in eclipse.

3. Run the debug server on eclipse. The console should give you the port number that the debug server is listening to (default : 5678).

Setup rsys:
1. If you have root privileges on rsys install the python package 'pydevd'.
  pip install pydevd

2. If you do not have root privileges, use the target option in pip :
  pip  install  --target=d:\other\location  package_name

3. If you also do not have pip installed, download the package and install it to a custom directory. (refer https://docs.python.org/2/install/)
For 2. and 3., do not forget to add the custom directory to PYTHONPATH to import the package in your program.

Test the debugger:
1. Create a file hello_world.py and make sure it can be accessed both on rsys and dsys. (It should be the same file and not a copy of it)

2. Type the following into hello_world.py :

import pydevd
pydevd.settrace("10.X.Y.Z", port=5678)
# where 10.X.Y.Z is the IP address of dsys and 5678 is the port of the debug server running on dsys.

print "Hello World!"
# where your actual program goes.

3. In Eclipse (on dsys) create a new PyDev project including hello_world.py in its source. (Make sure the debugger is still running on port specified in the source file.)

4. Run hello_world.py on rsys. Hopefully your running application should be caught on the remote debug server running on Eclipse. (It may prompt you to choose the source file.)
Note: If break points do not seem to be working at this point, relevant paths need to be incorporated in the configuration for Eclipse and pydevd as below.

Configuration for project level debugging and working breakpoints:
(Refer to this pydevd documentation)

Important: Make sure you have the SAME source file structure mounted both on rsys and dsys. Unless there is a one-one correspondence between the files, adding breakpoints in eclipse editor on dsys will not be recognized by the program running on rsys and a warning will be displayed on rsys :
>pydev debugger: warning: trying to add breakpoint to file that does not exist:
/home/pi/python/f:/python projects/server/server.py (will have no effect)

1. Edit  the file pydevd_file_utils.py in the installed packages pydevd on rsys.
A portion of comments on that file explicitly instructs the corresponding project source paths on rsys and dsys be added to the file :
"E.g.:
        If the server (your python process) has the structure
            /user/projects/my_project/src/package/module1.py

        and the client has:
            c:\my_project\src\package\module1.py

        the PATHS_FROM_ECLIPSE_TO_PYTHON would have to be:
            PATHS_FROM_ECLIPSE_TO_PYTHON = [(r'c:\my_project\src', r'/user/projects/my_project/src')]"

4. In Eclipse, go to Window > Preferences > PyDev > Debug > Source Locator and add a similar entry as the one to pydevd_file_utils.py with the Path to translate being the path on rsys and Translated path the one on dsys.