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Debugging Scipion with PyCharm

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Course presentation

Configuring PyCharm


We assume you have Scipion3 installed and PyCharm configured

We will learn how to add run configurations to skip scipion3 launcher and to be able to use PyCharm “debug” button straight away with many of the Scipion modes (tests, project, config, …) We will also learn how to attach to a “protocol process” to debug its steps.

Cloning and installing scipion-em-template

If you are following a course you might already have done this:

cd desired/location
git clone
cd scipion3/location
./scipion3 installp -p scipion-em-template/location --devel

Checking out the empiar_download branch

Check out the empiar_download branch

git checkout empiar_download

Creating the debugging project

Open Scipion and create a new project called “debugging”.


The name is not relevant but we’ll be referring to the project or folders associated using that name from now on.

Find (Ctrl+F) the “myplugin - empiar downloader” protocol and save it. No need to execute it for now. You can close Scipion.

Skipping the scipion3 launcher in PyCharm configurations

Add a new PyCharm configuration: it can be used to easily execute commands in one click. To create a new configuration, click on Add Configuration > + > python:

pycharm create configuration

Set the values according to the image below

pycharm create direct configuration
  1. Name: scipion3 last.

  2. Module name: Choose module name in the dropdown list instead of the script and then choose “scipion”

  3. Parameters: enter “last”. This will open directly the last modified project.

  4. Environment variables: You need to set 2 of them

  1. SCIPION_HOME=/path/where/scipion/is/installed

  2. LD_LIBRARY_PATH=/path/where/scipion/is/installed/software/lib

  1. Python interpreter: /path/to/.scipion3env/bin/python

  2. Working directory: same as SCIPION_HOME

“Apply” and you’ll have now a “direct” run/debug PyCharm configuration.


Duplicating this configuration and changing the “Parameters” field and “Name” will provide you more direct run configurations for other scipion modes like “tests”, “config”, … Type scipion3 help to discover them.

Testing the direct configuration

Set a breakpoint at scipion-app/scipion/ in the first import line by clicking in the empty space between the line number and the import line. A red dot should appear

Click on the “Green bug” icon, or on Run>>Debug

PyCharm should stop execution at that breakpoint line.

Checkout this page to learn more about debugging in PyCharm.

Debugging the click on “Execute” button

Let’s debug what happens when you click on the “Execute” button in the protocol form. Set a breakpoint in scipion-pyworkflow/pyworkflow/gui/ at FormWindow.execute Don’t worry if you don’t understand all the code here. Click on the debug icon. The last project should open (debugging project). Edit the saved protocol and click on the “Execute” button.

Ready to debug the click on Execute button

Try to understand:

  1. How the protocol validation happens?


If you find hard to reach the protocol._validate method from the execute, set a breakpoint in the myplugin/protocols/protocol_empiar_download at EmpiarDownloader._validate and wait there.

  1. Try to reach the point where the new process for the protocol is created (at pyworkflow.protocol.launch._launchLocal)

Debugging the protocol execution

Protocol execution happens in a new process. There is no way to reach it using the “IDE debugging” configuration. For this you need to be able to attach to the protocol’s process. It is very likely that the executing code will be faster than you, clicking on the IDE menus to attach to the process. Thus, you need to “delay” the execution using sleep(10).

Delaying “TEMPORARILY” the protocol process

Go to and add the TEMPORARY delay after the “if __main__” check:

if __name__ == '__main__':
    import time

This will give you some time.


Do not forget to remove the time.sleep(10) when done or you’ll be delaying execution by 10 seconds

Now, edit the “empiar-downloader” protocol and execute it. Go back to PyCharm and click on Run > Attach to process (a window should pop up with a list of python processes) Look for the one like /path/to/pyworkflow/apps/ /path/to/project/Runs/000353_EmpiarDownloader/logs/run.db 353

PyCharm attach to process window

Other frequent debugging points to add the sleep to are _insertAllSteps, or a specific step method.